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18 pages, 2417 KiB

Open AccessArticle

Radiological Characteristics of Carbonated Portland Cement Mortars Made with GGBFS

by Miguel Ángel Sanjuán, José Antonio Suárez-Navarro, Cristina Argiz, Marta Barragán, Guillermo Hernáiz, Miriam Cortecero and Pedro Lorca

Materials 2022, 15(9), 3395; https://doi.org/10.3390/ma15093395 - 09 May 2022

Cited by 2 | Viewed by 1280

Abstract

The objective of this study is to assess whether the carbonation process can modify the physicochemical characteristics of the natural radionuclides of the three natural radioactive series, together with ⁴⁰K. Three mortar specimens with different percentages of ground granulated blast-furnace slag (GGBFS), [...] Read more.

The objective of this study is to assess whether the carbonation process can modify the physicochemical characteristics of the natural radionuclides of the three natural radioactive series, together with ⁴⁰K. Three mortar specimens with different percentages of ground granulated blast-furnace slag (GGBFS), cured under water for 1, 3, 7, 14, or 28 days, were subjected to a natural carbonation process. Activity concentrations for the solid and ground mortars were determined by gamma spectrometry and by radiochemical separation of isotopic uranium. The novelty of this paper relies principally on the study we have carried out, for the first time, of the radiological characteristics of carbonated Portland cement mortars. It was found that the chemical properties of the 3 mortar specimens were not affected by the carbonation process, with particular attention placed on uranium (²³⁸U, ²³⁵U, and ²³⁴U), the activity concentrations of which were equivalent to the ²²⁶Ra results and ranged from 5.5 ± 1.6 Bq kg⁻¹ to 21.4 ± 1.2 Bq kg⁻¹ for the ²³⁸U. The average activity concentrations for the 3 types of mortars were lower than 20.1 Bq kg⁻¹, 14.5 Bq kg⁻¹, and 120.2 Bq kg⁻¹ for the ²²⁶Ra, ²³²Th (²¹²Pb), and ⁴⁰K, respectively. Annual effective dose rates were equivalent to the natural background of 0.024 mSv. In addition, it was observed that the variation rate for the ²²²Rn emanation was due primarily to the Portland cement hydration and not due to the pore size redistribution as a consequence of the carbonation process. This research will provide new insights into the potential radiological risk from carbonated cement-based materials. Moreover, the assessment that is presented in this study will convey valuable information for future research that will explore the activity concentration of building materials containing NORM materials. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 13674 KiB

Open AccessArticle

Seismic Performance of Steel-Reinforced Concrete Columns with Q690 High-Strength Steel

by Jun Wang, Xinyu Yi, Qi Liu and Xueqi Fang

Materials 2022, 15(9), 2979; https://doi.org/10.3390/ma15092979 - 19 Apr 2022

Cited by 6 | Viewed by 1810

Abstract

In this paper, based on the low-cycle loading tests of 11 steel-reinforced concrete (SRC) frame columns with built-in Q690 steel and 5 SRC frame columns with built-in Q235 steel, a systematic study on their seismic performance was carried out. The design parameters of [...] Read more.

In this paper, based on the low-cycle loading tests of 11 steel-reinforced concrete (SRC) frame columns with built-in Q690 steel and 5 SRC frame columns with built-in Q235 steel, a systematic study on their seismic performance was carried out. The design parameters of the specimens were the steel strength, axial compression ratio, shear span ratio, steel content, and stirrup ratio. The failure modes, stress characteristics, hysteresis curve, skeleton curve, displacement ductility performance, energy dissipation capacity, and other main seismic indicators of the specimens with different parameters were analyzed, and the corresponding relationship between the displacement ductility performance of the specimen and the energy dissipation capacity and design parameters was obtained. The results show that the load–displacement curve of the specimens is relatively full, the descending section is gentle, and various seismic performance indicators are relatively excellent, reflecting good seismic performance. Equipped with high-strength steel SRC frame columns, they can better bear the horizontal load, the displacement ductility performance is improved, and the energy dissipation capacity is slightly lower than that of ordinary-strength steel SRC frame columns. The increase in the shear span ratio, steel content, and stirrup ratio of the specimens helps to improve their seismic performance, whereas an increase in the axial compression ratio makes their seismic performance worse. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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10 pages, 2625 KiB

Open AccessArticle

Effect of Sulfate Concentration on Chloride Diffusion of Concrete under Cyclic Load

by Demei Yu, Chao Feng, Tengfei Fu and Aiqin Shen

Materials 2022, 15(6), 2036; https://doi.org/10.3390/ma15062036 - 10 Mar 2022

Cited by 3 | Viewed by 1391

Abstract

The existence of chloride ions, sulfate ions, and vehicle dynamic loads may lead to a shortened service life and premature failure of the road and bridge structures in northwestern China. Immersed in a dual-salt solution while simultaneously applying cyclic flexural loads, the free [...] Read more.

The existence of chloride ions, sulfate ions, and vehicle dynamic loads may lead to a shortened service life and premature failure of the road and bridge structures in northwestern China. Immersed in a dual-salt solution while simultaneously applying cyclic flexural loads, the free chloride ion concentration and erosion depth in concrete specimens were measured. The influence of the sulfate concentration on the apparent surface chloride concentration (C_s) and apparent diffusion coefficient (D_app) was studied. An exponential model was used to fit the C_s, and the influence of sulfate concentration on the C_s was analyzed. The result showed that cyclic loading and solution concentration were two primary factors affecting chloride diffusion. Meanwhile, compared with the emersion conditions, dynamic loading would induce significantly accelerated chloride ion penetration. Under the coupling effect of sulfate and dynamic loading, as the sulfate concentration increased, the chloride ion concentration and erosion depth were both decreased. The existence of sulfate ions improved the chloride ion penetration resistance of concrete. The results provide insight in designing concrete in regions where multiple salt ingression (sulfate and chloride) is a major durability issue of the structures. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 2832 KiB

Open AccessArticle

Cross-Sectional Analysis of the Resistance of RC Members Subjected to Bending with/without Axial Force

by Marek Lechman

Materials 2022, 15(5), 1957; https://doi.org/10.3390/ma15051957 - 06 Mar 2022

Cited by 4 | Viewed by 1932

Abstract

This paper deals with the cross-sectional analysis of the resistance of RC members subjected to a bending moment with or without axial forces. To determine section resistance, the nonlinear material law for concrete in compression is assumed according to Eurocode 2, taking into [...] Read more.

This paper deals with the cross-sectional analysis of the resistance of RC members subjected to a bending moment with or without axial forces. To determine section resistance, the nonlinear material law for concrete in compression is assumed according to Eurocode 2, taking into account the effect of concrete softening. It adequately describes the concrete behavior of RC members up to failure. The idealized stress–strain relation for the reinforcing steel is assumed. For the ring cross-section subjected to bending with axial force and for areas weakened by an opening, normalized resistances have been derived by integrating corresponding equilibrium equations. They are presented in the form of interaction curves and compared with the results of testing conducted on RC eccentrically loaded columns. Furthermore, the ultimate normalized bending moment has been derived for the RC rectangle subjected to bending without axial force. It was applied to the cross-sectional analysis of steel and concrete composite beams consisting of the RC rectangular core located inside a reversed TT-welded profile. Comparative analysis indicated good agreements between the proposed section models and experimental data. The objective of the paper is the dimensioning optimization of the considered cross-sections with the fulfillment of structural safety requirements. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 3066 KiB

Open AccessArticle

Studies on Cement Pastes Exposed to Water and Solutions of Biological Waste

by Agnieszka Sujak, Michał Pyzalski, Karol Durczak, Tomasz Brylewski, Paweł Murzyn and Krzysztof Pilarski

Materials 2022, 15(5), 1931; https://doi.org/10.3390/ma15051931 - 04 Mar 2022

Cited by 3 | Viewed by 1485

Abstract

The paper presents studies on the early stages of biological corrosion of ordinary Portland cements (OPC) subjected to the reactive media from the agricultural industry. For ten months, cement pastes of CEM I type with various chemical compositions were exposed to pig slurry, [...] Read more.

The paper presents studies on the early stages of biological corrosion of ordinary Portland cements (OPC) subjected to the reactive media from the agricultural industry. For ten months, cement pastes of CEM I type with various chemical compositions were exposed to pig slurry, and water was used as a reference. The phase composition and structure of hydrating cement pastes were characterized by X-ray diffraction (XRD), thermal analysis (DTA/TG/DTG/EGA), and infrared spectroscopy (FT-IR). The mechanical strength of the cement pastes was examined. A 10 to 16% decrease in the mechanical strength of the samples subjected to pig slurry was observed. The results indicated the presence of thaumasite (C₃S·CO₂·SO₃·15H₂O) as a biological corrosion product, likely formed by the reaction of cement components with living matter resulting from the presence of bacteria in pig slurry. Apart from thaumasite, portlandite (Ca(OH)₂)—the product of hydration—as well as ettringite (C₃A·3CaSO₄·32H₂O) were also observed. The study showed the increase in the calcium carbonate (CaCO₃) phase. The occurrence of unreacted phases of cement clinker, i.e., dicalcium silicate (C₂S) and tricalcium aluminate (C₃A), in the samples was confirmed. The presence of thaumasite phase and the exposure condition-dependent disappearance of CSH phase (calcium silicate hydrate), resulting from the hydration of the cements, were demonstrated. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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22 pages, 10684 KiB

Open AccessArticle

Experimental Research on Mechanical Properties and Compression Constitutive Relationship of PVA Fiber-Reinforced Coral Concrete

by Lan Rao, Ling Wang and Yun Zheng

Materials 2022, 15(5), 1762; https://doi.org/10.3390/ma15051762 - 26 Feb 2022

Cited by 8 | Viewed by 1603

Abstract

In this paper, the mechanical properties of coral concrete with different strength and different polyvinyl alcohol (PVA) fiber content under compression were experimentally investigated. The results show that adding an appropriate amount of PVA fiber could obtain satisfactory mechanical properties of coral concrete. [...] Read more.

In this paper, the mechanical properties of coral concrete with different strength and different polyvinyl alcohol (PVA) fiber content under compression were experimentally investigated. The results show that adding an appropriate amount of PVA fiber could obtain satisfactory mechanical properties of coral concrete. The stress–strain constitutive relationship of plain and PVA fiber-reinforced coral concrete was investigated by prism uniaxial compression test. The results shown that the incorporation of PVA fiber had a significant effect on limiting the development of concrete internal cracks, and effectively improved the mechanical properties of coral concrete after cracking, especially the toughness. Different constitutive models from previous research were used to describe the axial compressive stress–strain relationship of plain and PVA fiber-reinforced coral concrete, and a piecewise function model was finally selected which is most consistent with the experimental curve and its characteristic points. In addition, determination of critical parameters for the selected constitutive model was proposed, and experimental validations confirmed its accuracy. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 3658 KiB

Open AccessArticle

Impact of Surfactant and Calcium Sulfate Type on Air-Entraining Effectiveness in Concrete

by Maciej Sypek, Rafał Latawiec, Beata Łaźniewska-Piekarczyk and Waldemar Pichór

Materials 2022, 15(3), 985; https://doi.org/10.3390/ma15030985 - 27 Jan 2022

Cited by 4 | Viewed by 2323

Abstract

The paper presents the evaluation of the influence of calcium sulfate on the air void microstructure in concrete and its action mechanism depending on the character of the air-entraining agent. Gypsum dehydration has been previously proven to negatively influence the air void structure [...] Read more.

The paper presents the evaluation of the influence of calcium sulfate on the air void microstructure in concrete and its action mechanism depending on the character of the air-entraining agent. Gypsum dehydration has been previously proven to negatively influence the air void structure of air-entrained concrete. Ettringite, nucleating from tricalcium aluminate and calcium sulfate, influences the adsorption and mode of action of anionic-based polycarboxylate ether admixtures. The authors suspected the admixture’s air-entraining mechanism was also affected by these characteristics. Gypsum dehydration was confirmed to influence the air void structure. In the case of the anionic surfactant, the content of air bubbles smaller than 300 µm was lower compared to cement with gypsum and hemihydrate. On the other hand, the content of air voids with a diameter up to 60 µm, which are the most favorable, was higher. The results obtained led to the conclusion that the mechanism of air entrainment was twofold, and in most cases occurred through the lowering of surface tension and/or through the adsorption of surfactant on cement grains. The adsorptive mechanism was proved to be more effective in terms of the total air content and the structure of the air void system. The results and conclusions of the study provide guidelines to determine the proper surfactant type to reduce the risk of improper air entrainment of concrete, and emphasize the importance of gypsum dehydration of cement in the process of air entrainment. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 34372 KiB

Open AccessArticle

High Temperature Degradation Mechanism of Concrete with Plastering Layer

by Chihao Liu and Jiajian Chen

Materials 2022, 15(2), 398; https://doi.org/10.3390/ma15020398 - 06 Jan 2022

Cited by 4 | Viewed by 1844

Abstract

At present, the research on the high temperature degradation of concrete usually focuses on only the degradation of concrete itself without considering the effect of the plastering layer. It is necessary to take into account the influence of the plastering layer on the [...] Read more.

At present, the research on the high temperature degradation of concrete usually focuses on only the degradation of concrete itself without considering the effect of the plastering layer. It is necessary to take into account the influence of the plastering layer on the high temperature degradation of concrete. With an increase in the water/cement ratio, the explosion of concrete disappeared. Although increasing the water/cement ratio can alleviate the cracking of concrete due to lower pressure, it leads to a decrease in the mechanical properties of concrete after heating. It is proved that besides the water/cement ratio, the apparent phenomena and mechanical properties of concrete at high temperature can be affected by the plastering layer. The plastering layer can relieve the high temperature cracking of concrete, and even inhibit the high temperature explosion of concrete with 0.30 water/cement ratio. By means of an XRD test, scanning electron microscope test and thermogravimetric analysis, it is found that the plastering layer can promote the rehydration of unhydrated cement particles of 0.30 water/cement ratio concrete at high temperature and then promote the mechanical properties of concrete at 400 °C. However, the plastering layer accelerated the thermal decomposition of C-S-H gel of concrete with a water/cement ratio of 0.40 at high temperature, and finally accelerate the decline of mechanical property of concrete. To conclude, the low water/cement ratio and plastering layer can delay the deterioration of concrete at high temperature. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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27 pages, 10318 KiB

Open AccessArticle

The Investigation on Mechanical Performances of High-Strength Steel Reinforced Concrete Composite Short Columns under Axial Load

by Jun Wang, Xinran Wang, Yuxin Duan, Yu Su and Xinyu Yi

Materials 2022, 15(1), 329; https://doi.org/10.3390/ma15010329 - 03 Jan 2022

Cited by 9 | Viewed by 1855

Abstract

At present, the existing standards (AISC360-16, EN1994-1-1:2004, and JGJ138-2016) lack relevant provisions for steel-reinforced concrete (SRC) composite columns with high-strength steel. To investigate the axial compressive mechanical performance of short high-strength steel-reinforced concrete (HSSRC) columns, the axial load test was conducted on 12 [...] Read more.

At present, the existing standards (AISC360-16, EN1994-1-1:2004, and JGJ138-2016) lack relevant provisions for steel-reinforced concrete (SRC) composite columns with high-strength steel. To investigate the axial compressive mechanical performance of short high-strength steel-reinforced concrete (HSSRC) columns, the axial load test was conducted on 12 short composite columns with high-strength steel and ordinary steel. The influences of steel strength, steel ratio, and the section form of steel on the failure modes, bearing capacity, and ductility of the specimens were studied. Afterward, the experimental data were compared with the existing calculation results. The results show: compared with the specimens with Q235 steel, the bearing capacity of the specimens with Q460 steel increases by 7.8–15.3%, the bearing capacity of the specimens with Q690 steel increases by 13.2–24.1%, but the ductility coefficient increases by 15.2–202.4%; with the increase of steel ratio, the bearing capacity and ductility of specimens are significantly improved. A change of the steel cross-section could influence the ductility of SRC columns more than their bearing capacity. Moreover, the calculation results show that present standards could not predict the bearing capacity of HSSRC columns. Therefore, a modified method for determining the effective strength of steel equipped in HSSRC columns was proposed. The results of the ABAQUS simulation also showed that the addition of steel fibers could significantly improve the bearing capacity of Q690 HSSRC columns. The research results provide a reference for engineering practices. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 51503 KiB

Open AccessArticle

Microstructure and Mechanical Property Evaluation of Dune Sand Reactive Powder Concrete Subjected to Hot Air Curing

by Sara Ahmed, Zin Mahaini, Farid Abed, Mohammad Abdul Mannan and Mufid Al-Samarai

Materials 2022, 15(1), 41; https://doi.org/10.3390/ma15010041 - 22 Dec 2021

Cited by 14 | Viewed by 2766

Abstract

The use of different sustainable materials in the manufacture of ultra-high-performance concrete (UHPC) is becoming increasingly common due to the unabating concerns over climate change and sustainability in the construction sector. Reactive powder concrete (RPC) is an UHPC in which traditional coarse aggregates [...] Read more.

The use of different sustainable materials in the manufacture of ultra-high-performance concrete (UHPC) is becoming increasingly common due to the unabating concerns over climate change and sustainability in the construction sector. Reactive powder concrete (RPC) is an UHPC in which traditional coarse aggregates are replaced by fine aggregates. The main purpose of this research is to produce RPC using dune sand and to study its microstructure and mechanical properties under different curing conditions of water curing and hot air curing. The effects of these factors are studied over a long-term period of 90 days. Quartz sand is completely replaced by a blend of crushed and dune sand, and cement is partially replaced by using binary blends of ground granulated blast furnace slag (GGBS) and fly ash (FA), which are used alongside silica fume (SF) to make a ternary supplementary binder system. Microstructural analysis is conducted using scanning electron microscopy (SEM), and engineering properties like compressive strength and flexural strength are studied to evaluate the performance of dune sand RPC. Overall, the results affirm that the production of UHPC is possible with the use of dune sand. The compressive strength of all mixes exceeded 120 MPa after 12 h only of hot air curing (HAC). The SEM results revealed the dense microstructure of RPC. However, goethite-like structures (corrosion products) were spotted at 90 days for all HAC specimens. Additionally, the use of FA accelerated the formation of such products as compared to GGBS. The effect of these products was insignificant from a mechanical point of view. However, additional research is required to determine their effect on the durability of RPC. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 2680 KiB

Open AccessArticle

Evaluation and Multi-Objective Optimization of Lightweight Mortars Parameters at Elevated Temperature via Box–Behnken Optimization Approach

by Mehmet Kaya, Zeynel Baran Yıldırım, Fuat Köksal, Ahmet Beycioğlu and Izabela Kasprzyk

Materials 2021, 14(23), 7405; https://doi.org/10.3390/ma14237405 - 02 Dec 2021

Cited by 8 | Viewed by 2155

Abstract

In this research, the mechanical properties of lightweight mortars containing different percentages of additional powder materials has been investigated using response surface methodology (RSM). Box–Behnken design, one of the RSM techniques, was used to study the effects of silica fume content (5, 10, [...] Read more.

In this research, the mechanical properties of lightweight mortars containing different percentages of additional powder materials has been investigated using response surface methodology (RSM). Box–Behnken design, one of the RSM techniques, was used to study the effects of silica fume content (5, 10, and 15%), vermiculite/cement (V/C) ratio (4, 6, and 8), and temperature (300, 600, and 900 °C) on the ultrasonic pulse velocity (UPV), bending strength, and compressive strength of lightweight mortars. Design expert statistical software was accustomed to determining and evaluating the mix-design of materials in mortar mixtures and temperature effect on mortars. After preliminary experimental research of the relationships between independent and response variables, regression models were built. During the selection of the model parameters, F value, p-value, and R² values of the statistical models were taken into account by using the backward elimination technique. The results showed a high correlation between the variables and responses. Multi-objective optimization results showed that the critical temperatures for different levels of silica fume (5–10–15%) were obtained as 371.6 °C, 306.3 °C, and 436 °C, respectively, when the V/C ratio kept constant as 4. According to the results obtained at high desirability levels, it is found that the UPS values varied in the range of 2480–2737 m/s, flexural strength of 3.13–3.81 MPa, and compressive strength of 9.9–11.5 MPa at these critical temperatures. As a result of this research, RSM is highly recommended to evaluate mechanical properties where concrete includes some additional powder materials and was exposed to high temperature. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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28 pages, 56664 KiB

Open AccessArticle

Mechanical Properties and Durability Performance of Concrete Containing Calcium Carbide Residue and Nano Silica

by Musa Adamu, Yasser E. Ibrahim, Mohamed E. Al-Atroush and Hani Alanazi

Materials 2021, 14(22), 6960; https://doi.org/10.3390/ma14226960 - 17 Nov 2021

Cited by 17 | Viewed by 2436

Abstract

Calcium carbide residue (CCR) is the end-product of production of acetylene gas for the applications such as welding, lighting, ripening of fruits, and cutting of metals. Due to its high pH value, disposing of CCR as a landfill increases the alkalinity of the [...] Read more.

Calcium carbide residue (CCR) is the end-product of production of acetylene gas for the applications such as welding, lighting, ripening of fruits, and cutting of metals. Due to its high pH value, disposing of CCR as a landfill increases the alkalinity of the environment. Therefore, due to its high calcium content, CCR is mostly blended with other pozzolanic materials, together with activators as binders in the cement matrix. In this study, cement was partially substituted using CCR at 0%, 7.5%, 15%, 22.5% and 30% by weight replacement, and nano silica (NS) was utilized as an additive by weight of binder materials at 0%, 1%, 2%, 3% and 4%. The properties considered were the slump, the compressive strength, the flexural strength, the splitting tensile strength, the modulus of elasticity, and the water absorption capacity. The microstructural properties of the concrete were also examined through FESEM and XRD analysis. The results showed that both CCR and NS increase the concrete’s water demand, hence reducing its workability. Mixes containing up to 15% CCR only showed improved mechanical properties. The combination of CCR and NS significantly improved the mechanical properties and decreased the concrete’s water absorption through improved pozzolanic reactivity as verified by the FESEM and XRD results. Furthermore, the microstructure of the concrete was explored, and the pores were refined by the pozzolanic reaction products. The optimum mix combination was obtained by replacing 15% cement using CCR and the addition of 2% NS by weight of cementitious materials. Therefore, using a hybrid of CCR and NS in concrete will result in reduction of cement utilization in concrete, leading to improved environmental sustainability and economy. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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22 pages, 6049 KiB

Open AccessArticle

The Influence of Gum Arabic Admixture on the Mechanical Properties of Lime-Metakaolin Paste Used as Binder in Hemp Concrete

by Przemysław Brzyski

Materials 2021, 14(22), 6775; https://doi.org/10.3390/ma14226775 - 10 Nov 2021

Cited by 15 | Viewed by 2559

Abstract

Organic admixtures based on polysaccharides are used in construction for modifying the properties of mortars and concretes. Gum arabic is an example of a polysaccharide-based biopolymer. The aim of the article was to investigate the possibilities of improving the strength parameters of a [...] Read more.

Organic admixtures based on polysaccharides are used in construction for modifying the properties of mortars and concretes. Gum arabic is an example of a polysaccharide-based biopolymer. The aim of the article was to investigate the possibilities of improving the strength parameters of a binder paste based on hydrated lime and metakaolin. The paste was modified with powdered gum arabic at 1%, 3% and 5% (by mass) as a partial replacement for the binder mix. The influence of the admixture on the pore size distribution as well as flexural and compressive strength was investigated. The admixture enhanced the total porosity of the paste, increasing the pore diameter compared with the reference formulation. The increase in porosity, in turn, did not reduce the mechanical strength. Conversely, the admixture in the amount of 3% and 5% caused a significant increase in the flexural (by about 300% in relation to reference paste) and compressive strengths (by 25% and 60%, respectively). The tested pastes were used as a binder in a composite based on hemp shives. The influence of binder modification on the water absorption and compressive strength of hemp concrete was tested. The strength of the composite soaked in water was also tested. The modification of the binder with gum arabic in the amount of 3% and 5% increased the compressive strength of hemp concrete (not soaked in water) by 53% and 92%, respectively and reduced the mass absorptivity by 6.6% and 10.4%, respectively. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 7612 KiB

Open AccessArticle

Laboratory Tests of Concrete Beams Reinforced with Recycled Steel Fibres and Steel Bars

by Małgorzata Pająk and Grzegorz Wandzik

Materials 2021, 14(22), 6752; https://doi.org/10.3390/ma14226752 - 09 Nov 2021

Cited by 6 | Viewed by 2664

Abstract

This paper explores the possibility of the partial replacement of the longitudinal reinforcement in reinforced concrete (RC) beams with recycled steel fibres (RSF). Testing was focused on the contribution of two volume ratios of the RSF—0.5%, 1.0%. Basic compression and flexural tensile tests [...] Read more.

This paper explores the possibility of the partial replacement of the longitudinal reinforcement in reinforced concrete (RC) beams with recycled steel fibres (RSF). Testing was focused on the contribution of two volume ratios of the RSF—0.5%, 1.0%. Basic compression and flexural tensile tests were performed to evaluate the effectiveness of the fibres following current standards. Additionally, the full-scale beams with and without conventional reinforcement were subjected to four-point bending tests. The results indicate that RSF improved the load-bearing capacity of the RC beams. Cooperation of RSF with the steel bars in carrying loads was proved. Findings from the Digital Image Correlation (DIC) revealed no impact on the cracking pattern of the RC beams. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 4306 KiB

Open AccessArticle

Efficient Use of Graphene Oxide and Silica Fume in Cement-Based Composites

by Ahmad Abdullah, Mohamed Taha, Mohamed Rashwan and Mohamed Fahmy

Materials 2021, 14(21), 6541; https://doi.org/10.3390/ma14216541 - 30 Oct 2021

Cited by 5 | Viewed by 1581

Abstract

Incorporation of graphene oxide (GO) and silica fume (SF) to cement composites enhances their mechanical properties if suitable proportional amounts of GO and SF are used. This study presents a simplified approach to determine experimentally the optimum GO and SF contents that should [...] Read more.

Incorporation of graphene oxide (GO) and silica fume (SF) to cement composites enhances their mechanical properties if suitable proportional amounts of GO and SF are used. This study presents a simplified approach to determine experimentally the optimum GO and SF contents that should be added to the cementitious mixture to obtain a proper and stable dispersion of GO sheets within the cement matrix. Composite mortar specimens with different GO and SF contents were designed and tested under flexural and compression loading. The phase formation and the microstructure of selected samples were also investigated to give an in-depth interpretation of the test results. The main criterion to determine the GO and SF contents was the ultimate strength required of the GO–cement composite. It was found that there was a composite interaction between the SF and GO contents in the cementitious mixture, which an envelope surface could describe if all other mix design parameters are kept constant. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 4332 KiB

Open AccessEditor’s ChoiceArticle

Influence of Firing Temperature on Phase Composition and Color Properties of Ceramic Tile Bodies

by Kornelia Wiśniewska, Waldemar Pichór and Ewelina Kłosek-Wawrzyn

Materials 2021, 14(21), 6380; https://doi.org/10.3390/ma14216380 - 25 Oct 2021

Cited by 5 | Viewed by 1621

Abstract

This study is focused on the behavior of the cream-firing clays from Opoczno region (Poland). The ceramic masses on which tests were carried out consisted of cream-firingBorkowice clay and dolomite in two different grain sizes as an additive that changes the color of [...] Read more.

This study is focused on the behavior of the cream-firing clays from Opoczno region (Poland). The ceramic masses on which tests were carried out consisted of cream-firingBorkowice clay and dolomite in two different grain sizes as an additive that changes the color of ceramic materials. Test samples were prepared by plastic method and fired at range of 1100–1240 °C. Phase composition of theinvestigated materials was characterized by XRD method with quantitive analysis of the amorphous phase determined by the Retvield technique. Color properties of the surface of the obtained ceramic materials were determined in CIE-Lab color space. The phase composition of the obtained ceramics depends on the firing temperature. The color of the surface of the ceramic materials also depends on the firing temperature. There was a tendency to decrease the brightness, decrease the blue shade, and increase the yellow shade of the surface of materials with increasing the temperature. The conducted tests allowed to conclude that the color of ceramic materials depends on their phase composition. The most important role in the formation of color correspond to the amorphous phase, formed during the process. The lower content of the amorphous phase in the material allows to obtain brighter products with a lower proportion of yellow, and therefore closer to white. Moreover, following tests were carried out: total water absorption, total open porosity, linear shrinkage, and flexural strength. With increasing the temperature, total water absorption and total open porosity decrease, and total linear shrinkage increases due to the progressive sintering process. Flexural strength increases with the increase of the firing temperature for materials consisting of Borkowice clay. The addition of dolomite introduced new pores into the material, which resulted in an increase in flexural strength at lower firing temperatures and a decrease in flexural strength at higher firing temperatures. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 5436 KiB

Open AccessArticle

Effect of Thermal Properties of Aggregates on the Mechanical Properties of High Strength Concrete under Loading and High Temperature Conditions

by Taegyu Lee, Keesin Jeong and Hyeonggil Choi

Materials 2021, 14(20), 6093; https://doi.org/10.3390/ma14206093 - 15 Oct 2021

Cited by 6 | Viewed by 1814

Abstract

The effect of the thermal properties of aggregates on the mechanical properties of high-strength concrete was evaluated under loading and high-temperature conditions. For the concrete, granite was selected as a natural aggregate, and ash-clay and clay as lightweight aggregates. The mechanical properties of [...] Read more.

The effect of the thermal properties of aggregates on the mechanical properties of high-strength concrete was evaluated under loading and high-temperature conditions. For the concrete, granite was selected as a natural aggregate, and ash-clay and clay as lightweight aggregates. The mechanical properties of the concrete (stress–strain, compressive strength, elastic modulus, thermal strain, and transient creep) were evaluated experimentally under uniform heating from 20 to 700 °C while maintaining the load at 0, 20, and 40% of the compressive strength at room temperature. Experimental results showed that the concrete containing lightweight aggregates had better mechanical properties, such as compressive strength and elastic modulus, than that of the concrete with a granite aggregate at high temperature. In particular, the concrete containing lightweight aggregates exhibited high compressive strength (60–80% of that at room temperature) even at 700 °C. Moreover, the concrete containing granite exhibited a higher thermal strain than that containing lightweight aggregates. The influence of the binding force under loaded conditions, however, was found to be larger for the latter type. The transient creep caused by the loading was constant regardless of the aggregate type below 500 °C but increased more rapidly when the coefficient of the thermal expansion of the aggregate was above 500 °C. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 4689 KiB

Open AccessArticle

Durability Properties of Ultra-High Performance Lightweight Concrete (UHPLC) with Expanded Glass

by Cristin Umbach, Alexander Wetzel and Bernhard Middendorf

Materials 2021, 14(19), 5817; https://doi.org/10.3390/ma14195817 - 05 Oct 2021

Cited by 10 | Viewed by 2350

Abstract

It is important to ensure the durability and safety of structures. In the case of newly developed materials that are outside the current rules, it is important to investigate all aspects of structural safety. The material studied in the following is a structural [...] Read more.

It is important to ensure the durability and safety of structures. In the case of newly developed materials that are outside the current rules, it is important to investigate all aspects of structural safety. The material studied in the following is a structural lightweight concrete with an ultra-high-performance matrix and expanded glass as a lightweight aggregate. The material, with a compressive strength of 60–100 MPa and a bulk density of 1.5–1.9 kg/dm³, showed high capillary porosities of 12 vol% (ultra-high-performance concretes (UHPC) < 5 vol%). Since the capillary porosity basically enables transport processes into the concrete, the material had to be examined more closely from the aspect of durability. Freeze-thaw resistance (68 g/m²) and chemical attack with sulfate at pH 3.5 for 12 weeks (16 g/m²) showed no increase in concrete corrosion. Targeted carbonation (0.53 mm/year^0.5) and chloride penetration resistance (6.0 × 10⁻¹³ to 12.6 × 10⁻¹³ m²/s) also showed good results against reinforcement corrosion. The results show that most of the measured capillary pores resulted from the lightweight aggregate and were not all present as a pore system. Thus, the durability was only slightly affected and the concrete can be compared to an UHPC. Only the abrasion resistance showed an increased value (22,000 mm³/5000 mm²), which, however, only matters if the material is used as a screed. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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27 pages, 10279 KiB

Open AccessArticle

Flexural Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Beams after Exposure to High Temperatures

by How-Ji Chen, Chien-Chuan Chen, Hung-Shan Lin, Shu-Ken Lin and Chao-Wei Tang

Materials 2021, 14(18), 5400; https://doi.org/10.3390/ma14185400 - 18 Sep 2021

Cited by 5 | Viewed by 2041

Abstract

Due to the dense structure of ultra-high-performance concrete (UHPC), it is prone to explosive spalling at high temperatures. In this paper, flexural testing of UHPC and high-strength concrete (HSC) beams was carried out at room temperature and after being subjected to different levels [...] Read more.

Due to the dense structure of ultra-high-performance concrete (UHPC), it is prone to explosive spalling at high temperatures. In this paper, flexural testing of UHPC and high-strength concrete (HSC) beams was carried out at room temperature and after being subjected to different levels of thermal exposure (300–500 °C). The cross-section of the beam specimen was 150 (width) × 200 (depth) mm, and its length was 1500 mm. The flexural and shear design of the beam specimens were carried out in accordance with the ACI 318M-14 code. All of the beams were singly reinforced with two #4 rebars (minimum reinforcement ratio) as a longitudinal tensile reinforcement at the bottom of the specimen and at an effective depth of 165 mm. The flexural load was applied using the three-point load method. The results show that, at room temperature and after being subjected to different thermal exposures, compared with the HSC specimens, the stiffness of the UHPC specimens in the post-cracking stage was relatively larger and the deflection under a given load was smaller. Moreover, whether at room temperature or after exposure to different thermal exposures, the ductility of the UHPC specimens was better than that of the HSC specimens. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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11 pages, 1963 KiB

Open AccessArticle

Removal Effect of Basic Oxygen Furnace Slag Porous Asphalt Concrete on Copper and Zinc in Road Runoff

by Tianyuan Yang, Meizhu Chen and Shaopeng Wu

Materials 2021, 14(18), 5327; https://doi.org/10.3390/ma14185327 - 16 Sep 2021

Cited by 3 | Viewed by 2060

Abstract

In order to improve the utilization efficiency of road runoff and the remove effects of heavy metals, porous asphalt pavements have been used as an effective measure to deal with heavy metals in road runoff. However, the removal effect on dissolved heavy metal [...] Read more.

In order to improve the utilization efficiency of road runoff and the remove effects of heavy metals, porous asphalt pavements have been used as an effective measure to deal with heavy metals in road runoff. However, the removal effect on dissolved heavy metal is weak. In this paper, basic oxygen furnace (BOF) slag was used as aggregate in porous asphalt concrete to improve the removal capacity of heavy metal. Road runoff solution with a copper concentration of 0.533 mg/L and a zinc concentration of 0.865 mg/L was artificially synthesized. The removal effect of BOF slag porous asphalt concrete on cooper and zinc in runoff was evaluated by removal tests. The influence of rainfall intensity and time on the removal effect was discussed. The results obtained indicated that BOF slag porous asphalt concrete has a better removal effect on copper. The removal rate of copper is 57–79% at the rainfall intensity of 5–40 mm/h. The removal rate of zinc is more susceptible to the changes of rainfall intensity than copper. The removal rate of zinc in heavy rain conditions (40 mm/h) is only 25%. But in light rain conditions (5 mm/h), BOF slag porous asphalt concrete maintains favorable removal rates of both copper and zinc, which are more than 60%. The heavy metal content of runoff infiltrating through the BOF slag porous asphalt concrete meets the requirements for irrigation water and wastewater discharge. The results of this study provide evidence for the environmentally friendly reuse of BOF slag as a road material and the improvement of the removal of heavy metal by porous asphalt concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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12 pages, 6163 KiB

Open AccessArticle

Precise Simulation of Heat-Flow Coupling of Pipe Cooling in Mass Concrete

by Peng Yu, Ruiqing Li, Dapeng Bie, Xiancai Liu, Xiaomin Yao and Yahui Duan

Materials 2021, 14(18), 5142; https://doi.org/10.3390/ma14185142 - 08 Sep 2021

Cited by 1 | Viewed by 1966

Abstract

For a long time, temperature control and crack prevention of mass concrete is a difficult job in engineering. For temperature control and crack prevention, the most effective and common-used method is to embed cooling pipe in mass concrete. At present, there still exists [...] Read more.

For a long time, temperature control and crack prevention of mass concrete is a difficult job in engineering. For temperature control and crack prevention, the most effective and common-used method is to embed cooling pipe in mass concrete. At present, there still exists some challenges in the precise simulation of pipe cooling in mass concrete, which is a complex heat-flow coupling problem. Numerical simulation is faced with the problem of over-simplification and inaccuracy. In this study, precise simulation of heat-flow coupling of pipe cooling in mass concrete is carried out based on finite element software COMSOL Multiphysics 5.4. Simulation results are comprehensively verified with results from theoretical solutions and equivalent algorithms, which prove the correctness and feasibility of precise simulation. Compared with an equivalent algorithm, precise simulation of pipe cooling in mass concrete can characterize the sharp temperature gradient around cooling pipe and the temperature rise of cooling water along pipeline more realistically. In addition, the cooling effects and local temperature gradient under different water flow (0.60 m³/h, 1.20 m³/h, and 1.80 m³/h) and water temperature (5 °C, 10 °C, and 15 °C) are comprehensively studied and related engineering suggestions are given. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 4908 KiB

Open AccessEditor’s ChoiceArticle

Investigation of Graphene Derivatives on Electrical Properties of Alkali Activated Slag Composites

by Wu-Jian Long, Xuan-Han Zhang, Bi-Qin Dong, Yuan Fang, Tao-Hua Ye and Jing Xie

Materials 2021, 14(16), 4374; https://doi.org/10.3390/ma14164374 - 04 Aug 2021

Cited by 5 | Viewed by 1546

Abstract

Reduced graphene oxide (rGO) has been widely used to modify the mechanical performance of alkali activated slag composites (AASC); however, the mechanism is still unclear and the electrical properties of rGO reinforced AASC are unknown. Here, the rheological, mechanical, and electrical properties of [...] Read more.

Reduced graphene oxide (rGO) has been widely used to modify the mechanical performance of alkali activated slag composites (AASC); however, the mechanism is still unclear and the electrical properties of rGO reinforced AASC are unknown. Here, the rheological, mechanical, and electrical properties of the AASC containing rGO nanosheets (0, 0.1, 0.2, and 0.3% wt.) are investigated. Results showed that rGO nanosheets addition can significantly improve the yield stress, plastic viscosity, thixotropy, and compressive strength of the AASC. The addition of 0.3% wt. rGO nanosheets increased the stress, viscosity, thixotropy, and strength by 186.77 times, 3.68 times, 15.15 times, and 21.02%, respectively. As for electrical properties, the impedance of the AASC increased when the rGO content was less than 0.2% wt. but decreased with the increasing dosage. In contrast, the dielectric constant and electrical conductivity of the AASC containing rGO nanosheets decreased and then increased, which can be attributed to the abundant interlayer water and the increasing structural defects as the storage sites for charge carriers, respectively. In addition, the effect of graphene oxide (GO) on the AASC is also studied and the results indicated that the agglomeration of GO nanosheets largely inhibited the application of it in the AASC, even with a small dosage. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 12312 KiB

Open AccessEditor’s ChoiceArticle

Applying Mixture of Municipal Incinerator Bottom Ash and Sewage Sludge Ash for Ceramic Tile Manufacturing

by Deng-Fong Lin, Wei-Jhu Wang, Chia-Wen Chen and Kuo-Liang Lin

Materials 2021, 14(14), 3863; https://doi.org/10.3390/ma14143863 - 10 Jul 2021

Cited by 4 | Viewed by 2396

Abstract

Municipal incinerator bottom ash (MIBA) and sewage sludge ash (SSA) are secondary wastes produced from municipal incinerators. Landfills, disposal at sea, and agricultural use have been the major outlets for these secondary wastes. As global emphasis on sustainability arises, many have called for [...] Read more.

Municipal incinerator bottom ash (MIBA) and sewage sludge ash (SSA) are secondary wastes produced from municipal incinerators. Landfills, disposal at sea, and agricultural use have been the major outlets for these secondary wastes. As global emphasis on sustainability arises, many have called for an increasing reuse of waste materials as valuable resources. In this study, MIBA and SSA were mixed with clay for ceramic tile manufacturing in this study. Raw materials firstly went through TCLP (Toxicity Characteristic Leaching Procedure) to ensure their feasibility for reuse. From scanning electron microscopy (SEM), clay’s smooth surface was contrasted with the porous surface of MIBA and SSA, which led to a higher water requirement for the mixing. Specimens with five MIBA mix percentages of 0%, 5%, 10%, 15%, and 20% (wt) and three SSA mix percentages of 0%, 10%, and 20% (wt) were made to compare how the two waste materials affected the quality of the final product and to what extent. Shrinkage tests showed that MIBA and SSA contributed oppositely to tile shrinkage, as more MIBA reduced tile shrinkage, while more SSA encouraged tile shrinkage. However, as the kiln temperature reached 1150 °C, the SiO2-rich SSA adversely reduced the shrinkage due to the glass phase that formed to expand the tile instead. Both MIBA and SSA increased water tile absorption and reduced its bending strength and wear resistance. Increasing the kiln temperature could effectively improve the water absorption, bending strength, and wear resistance of high MIBA and SSA mixes, as SEM showed a more compact structure at higher temperatures. However, when the temperature reached 1100 °C, more pores appeared and seemingly exhausted the benefit brought by the higher temperature. Complex interactions between kiln temperature and MIBA/SSA mix percentage bring unpredictable performance of tile shrinkage, bending strength, and water absorption, which makes it very challenging to create a sample meeting all the specification requirements. We conclude that a mix with up to 20% of SSA and 5% of MIBA could result in quality tiles meeting the requirements for interior or exterior flooring applications when the kiln temperature is carefully controlled. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 6702 KiB

Open AccessArticle

Physicochemical, Mineralogical, and Mechanical Properties of Calcium Aluminate Cement Concrete Exposed to Elevated Temperatures

by Amirmohamad Abolhasani, Bijan Samali and Fatemeh Aslani

Materials 2021, 14(14), 3855; https://doi.org/10.3390/ma14143855 - 09 Jul 2021

Cited by 13 | Viewed by 2222

Abstract

One commonly used cement type for thermal applications is CAC containing 38–40% alumina, although the postheated behavior of this cement subjected to elevated temperature has not been studied yet. Here, through extensive experimentation, the postheated mineralogical and physicochemical features of calcium aluminate cement [...] Read more.

One commonly used cement type for thermal applications is CAC containing 38–40% alumina, although the postheated behavior of this cement subjected to elevated temperature has not been studied yet. Here, through extensive experimentation, the postheated mineralogical and physicochemical features of calcium aluminate cement concrete (CACC) were examined via DTA/TGA, X-ray diffraction (XRD), and scanning electron microscopy (SEM) imaging and the variation in the concrete physical features and the compressive strength deterioration with temperature rise were examined through ultrasonic pulse velocity (UPV) values. In addition, other mechanical features that were addressed were the residual tensile strength and elastic modulus. According to the XRD test results, with the temperature rise, the dehydration of the

C_{3} A H_{6}

structure occurred, which, in turn, led to the crystallization of the monocalcium dialuminate (

C A_{2}

) and alumina (

A l_{2} O_{3}

) structures. The SEM images indicated specific variations in morphology that corresponded to concrete deterioration due to heat. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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31 pages, 16563 KiB

Open AccessEditor’s ChoiceArticle

Reduced Order Multiscale Simulation of Diffuse Damage in Concrete

by Giao Vu, Fabian Diewald, Jithender J. Timothy, Christoph Gehlen and Günther Meschke

Materials 2021, 14(14), 3830; https://doi.org/10.3390/ma14143830 - 08 Jul 2021

Cited by 7 | Viewed by 2461

Abstract

Damage in concrete structures initiates as the growth of diffuse microcracks that is followed by damage localisation and eventually leads to structural failure. Weak changes such as diffuse microcracking processes are failure precursors. Identification and characterisation of these failure precursors at an early [...] Read more.

Damage in concrete structures initiates as the growth of diffuse microcracks that is followed by damage localisation and eventually leads to structural failure. Weak changes such as diffuse microcracking processes are failure precursors. Identification and characterisation of these failure precursors at an early stage of concrete degradation and application of suitable precautionary measures will considerably reduce the costs of repair and maintenance. To this end, a reduced order multiscale model for simulating microcracking-induced damage in concrete at the mesoscale level is proposed. The model simulates the propagation of microcracks in concrete using a two-scale computational methodology. First, a realistic concrete specimen that explicitly resolves the coarse aggregates in a mortar matrix was generated at the mesoscale. Microcrack growth in the mortar matrix is modelled using a synthesis of continuum micromechanics and fracture mechanics. Model order reduction of the two-scale model is achieved using a clustering technique. Model predictions are calibrated and validated using uniaxial compression tests performed in the laboratory. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 7971 KiB

Open AccessArticle

Computational Generation of Virtual Concrete Mesostructures

by Vijaya Holla, Giao Vu, Jithender J. Timothy, Fabian Diewald, Christoph Gehlen and Günther Meschke

Materials 2021, 14(14), 3782; https://doi.org/10.3390/ma14143782 - 06 Jul 2021

Cited by 20 | Viewed by 2905

Abstract

Concrete is a heterogeneous material with a disordered material morphology that strongly governs the behaviour of the material. In this contribution, we present a computational tool called the Concrete Mesostructure Generator (CMG) for the generation of ultra-realistic virtual concrete morphologies for mesoscale and [...] Read more.

Concrete is a heterogeneous material with a disordered material morphology that strongly governs the behaviour of the material. In this contribution, we present a computational tool called the Concrete Mesostructure Generator (CMG) for the generation of ultra-realistic virtual concrete morphologies for mesoscale and multiscale computational modelling and the simulation of concrete. Given an aggregate size distribution, realistic generic concrete aggregates are generated by a sequential reduction of a cuboid to generate a polyhedron with multiple faces. Thereafter, concave depressions are introduced in the polyhedron using Gaussian surfaces. The generated aggregates are assembled into the mesostructure using a hierarchic random sequential adsorption algorithm. The virtual mesostructures are first calibrated using laboratory measurements of aggregate distributions. The model is validated by comparing the elastic properties obtained from laboratory testing of concrete specimens with the elastic properties obtained using computational homogenisation of virtual concrete mesostructures. Finally, a 3D-convolutional neural network is trained to directly generate elastic properties from voxel data. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 9542 KiB

Open AccessArticle

Mechanical and Microstructural Characteristics of Calcium Sulfoaluminate Cement Exposed to Early-Age Carbonation Curing

by Weikang Wang, Xuanchun Wei, Xinhua Cai, Hongyang Deng and Bokang Li

Materials 2021, 14(13), 3515; https://doi.org/10.3390/ma14133515 - 24 Jun 2021

Cited by 10 | Viewed by 2226

Abstract

The early-age carbonation curing technique is an effective way to improve the performance of cement-based materials and reduce their carbon footprint. This work investigates the early mechanical properties and microstructure of calcium sulfoaluminate (CSA) cement specimens under early-age carbonation curing, considering five factors: [...] Read more.

The early-age carbonation curing technique is an effective way to improve the performance of cement-based materials and reduce their carbon footprint. This work investigates the early mechanical properties and microstructure of calcium sulfoaluminate (CSA) cement specimens under early-age carbonation curing, considering five factors: briquetting pressure, water–binder (w/b) ratio, starting point of carbonation curing, carbonation curing time, and carbonation curing pressure. The carbonization process and performance enhancement mechanism of CSA cement are analyzed by mercury intrusion porosimetry (MIP), thermogravimetry and derivative thermogravimetry (TG-DTG) analysis, X-ray diffraction (XRD), and scanning electron microscope (SEM). The results show that early-age carbonation curing can accelerate the hardening speed of CSA cement paste, reduce the cumulative porosity of the cement paste, refine the pore diameter distribution, and make the pore diameter distribution more uniform, thus greatly improving the early compressive strength of the paste. The most favorable w/b ratio for the carbonization reaction of CSA cement paste is between 0.15 and 0.2; the most suitable carbonation curing starting time point is 4 h after initial hydration; the carbonation curing pressure should be between 3 and 4 bar; and the most appropriate time for carbonation curing is between 6 and 12 h. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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12 pages, 1818 KiB

Open AccessArticle

Prediction Model of Concrete Initial Setting Time Based on Stepwise Regression Analysis

by Wei-Jia Liu, Xu-Jing Niu, Ning Yang, Yao-Shen Tan, Yu Qiao, Chun-Feng Liu, Kun Wu, Qing-Bin Li and Yu Hu

Materials 2021, 14(12), 3201; https://doi.org/10.3390/ma14123201 - 10 Jun 2021

Cited by 5 | Viewed by 2131

Abstract

Mass concrete is usually poured in layers. To ensure the interlayer bonding quality of concrete, the lower layer should be kept in a plastic state before the upper layer is added. Ultimately, it will lead to the prediction of concrete setting time as [...] Read more.

Mass concrete is usually poured in layers. To ensure the interlayer bonding quality of concrete, the lower layer should be kept in a plastic state before the upper layer is added. Ultimately, it will lead to the prediction of concrete setting time as a critical task in concrete pouring. In this experiment, the setting time of concrete in laboratory and field environments was investigated. The equivalent age of concrete at the initial setting was also analyzed based on the maturity theory. Meanwhile, factors affecting the setting time in the field environment were studied by means of multiple stepwise regression analysis. Besides, the interlayer splitting tensile strength of concrete subjected to different temperatures and wind speeds was determined. The results of laboratory tests show that both setting time and interlayer splitting tensile strength of concrete decrease significantly with the increase of air temperature and wind speed. In addition, the equivalent age of concrete at initial setting remains the same when subjected to different temperatures, while it decreases obviously with the increase of wind speed. In the field environment, the equivalent age of concrete at initial setting is greatly different, which is related to the variability of relative humidity and wind speed. The average air temperature and maximum wind speed are the main factors affecting the initial setting time of concrete. Furthermore, a prediction model is established based on the stepwise regression analysis results, which can predict the actual setting state in real-time, and hence controlling the interlayer bonding quality of dam concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 3221 KiB

Open AccessEditor’s ChoiceArticle

Simulation of the Attrition of Recycled Concrete Aggregates during Concrete Mixing

by Jaime Moreno-Juez, Luís Marcelo Tavares, Riccardo Artoni, Rodrigo M. de Carvalho, Emerson Reikdal da Cunha and Bogdan Cazacliu

Materials 2021, 14(11), 3007; https://doi.org/10.3390/ma14113007 - 01 Jun 2021

Cited by 9 | Viewed by 2490

Abstract

Concrete mixing can lead to mechanical degradation of aggregates, particularly when dealing with recycled concrete aggregates. In this work, the attrition of such materials during mixing is studied by means of experiments and simulations. The effect of the presence of fines, water addition, [...] Read more.

Concrete mixing can lead to mechanical degradation of aggregates, particularly when dealing with recycled concrete aggregates. In this work, the attrition of such materials during mixing is studied by means of experiments and simulations. The effect of the presence of fines, water addition, flow configuration of the mixer (co- or counter-current) and impeller frequency is discussed. Experiments were performed in a laboratory Eirich mixer. Discrete element numerical simulations (DEM) were performed on the same geometry by mimicking the behaviour of the material and, in particular, the cohesion induced by water and the cement paste using either Hertz–Mindlin or Hertz–Mindlin with Johnson–Kendall–Roberts (JKR) contact laws. The combination of the collision energy spectra extracted from the DEM simulations and an attrition model allowed the prediction of the mass loss due to attrition in 1-min experiments. Semi-quantitative agreement was observed between experiments and simulations, with a mean relative error of 26.4%. These showed that higher mass losses resulted from operation at the highest impeller speeds, co-current operation, and also with the wet aggregate. Mixing of the agglomerate in the concrete mix resulted in a significant reduction in attrition when compared to mixing aggregates alone. With further validation, the proposed simulation approach can become a valuable tool in the optimization of mixing by allowing the effects of material, machine and process variables to be studied on the mass loss due to attrition. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 2256 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Type of Cement on the Action of the Admixture Containing Aluminum Powder

by Justyna Kuziak, Kamil Zalegowski, Wioletta Jackiewicz-Rek and Emilia Stanisławek

Materials 2021, 14(11), 2927; https://doi.org/10.3390/ma14112927 - 29 May 2021

Cited by 3 | Viewed by 2417

Abstract

The study of the effect of cement type on the action of an admixture increasing the volume of concrete (containing aluminum powder), used in amounts of 0.5–1.5% of cement mass, was presented. The tests were carried out on cement mortars with Portland (CEM [...] Read more.

The study of the effect of cement type on the action of an admixture increasing the volume of concrete (containing aluminum powder), used in amounts of 0.5–1.5% of cement mass, was presented. The tests were carried out on cement mortars with Portland (CEM I) and ground granulated blast-furnace slag cement (CEM III). The following tests were carried out for the tested mortars: the air content in fresh mortars, compressive strength, flexural strength, increase in mortar volume, bulk density, pore structure evaluation (by the computer image analysis method) and changes in the concentration of OH⁻ ions during the hydration of used cements. Differences in the action of the tested admixture depending on the cement used were found. To induce the expansion of CEM III mortars, a smaller amount of admixture is required than in the case of CEM I cement. Using the admixture in amounts above 1% of the cement mass causes cracks of mortars with CEM III cement due to slow hydrogen evolution, which occurs after mortar plasticity is lost. The use of an aluminum-containing admixture reduces the strength properties of the cement mortars, the effect being stronger in the case of CEM III cement. The influence of the sample molding time on the admixture action was also found. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 3200 KiB

Open AccessArticle

Study on Preparation and Interfacial Transition Zone Microstructure of Red Mud-Yellow Phosphorus Slag-Cement Concrete

by Zhennan Su and Xianhai Li

Materials 2021, 14(11), 2768; https://doi.org/10.3390/ma14112768 - 23 May 2021

Cited by 14 | Viewed by 2569

Abstract

Open stockpiling and the continual production of industrial solid wastes such as red mud (RM) and yellow phosphorus slag (YPS) have caused serious environmental pollution issues. Additionally, concrete prepared easily and with high strength is a widely applied building material. Therefore, replacing part [...] Read more.

Open stockpiling and the continual production of industrial solid wastes such as red mud (RM) and yellow phosphorus slag (YPS) have caused serious environmental pollution issues. Additionally, concrete prepared easily and with high strength is a widely applied building material. Therefore, replacing part or all of the cement for preparing concrete with RM and YPS will greatly reduce this kind of solid waste and, thus, decrease environmental pressures. This study investigated the best ratio for the replacement of concrete with RM and YPS, testing the mechanical properties as well as the morphology, material composition, and microporous structure of the interface transition zone (ITZ). The results showed for the concrete prepared with ordinary Portland cement replaced by 10.00 wt.% RM and 18 wt.% YPS, compared to ordinary Portland cement concrete, the compressive strength of concrete with basalt aggregate and dolomite aggregate increased by 25.04% and 27.27%, respectively, when the concrete was cured with steam for 28 days. Furthermore, it had a smaller average pore diameter and crystal size in the ITZ. The aggregate and matrix were more closely intertwined. This was because RM had a low cementitious activity and mainly had a filling effect when added to concrete, while the highly active silica in YPS could react with the Ca(OH)₂ crystal (CH) produced from cement hydration to form calcium silicate hydrate (CSH) gel, improving the mechanical properties and microstructure of the concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 10561 KiB

Open AccessArticle

Prediction and Analysis of Ultimate Bearing Capacity of Square CFST Long Column under Eccentric Compression after Acid Rain Corrosion

by Xuetao Lyu, Liqiang Zhang, Tong Zhang, Ben Li, Huan Li and Yang Yu

Materials 2021, 14(10), 2568; https://doi.org/10.3390/ma14102568 - 14 May 2021

Cited by 10 | Viewed by 2063

Abstract

This paper adopts the method of steel tube wall thickness and strength reduction to simulate corrosion damage. The numerical model of the square concrete-filled steel tube long column (SCFST-LC) under eccentric compression after acid rain corrosion is established in the finite element software, [...] Read more.

This paper adopts the method of steel tube wall thickness and strength reduction to simulate corrosion damage. The numerical model of the square concrete-filled steel tube long column (SCFST-LC) under eccentric compression after acid rain corrosion is established in the finite element software, ABAQUS. The reliability and accuracy of the model are verified by comparing it with published relevant experimental results. The failure mode, load-deformation curve, and ultimate compressive load were analysed. Following that, the impacts of section size, yield strength of the steel tube, axial compressive strength of concrete, steel ratio, slenderness ratio, and load eccentricity on its ultimate compressive load are comprehensively investigated. The results demonstrate that the ultimate compressive load of the SCFST-LC decreases significantly with the increase in corrosion rate. The corrosion rate increases from 10 to 40%, and the ultimate bearing capacity decreases by 37.6%. Its ultimate bearing capacity can be enhanced due to the increase in section size, material strength, and steel ratio. In contrast, the ascending slenderness ratio and load eccentricity has harmful effects on the ultimate compressive load of the specimens. Finally, a simplified formula for the axial compressive load of the SCFST-LC under eccentric compression after acid rain corrosion is proposed. The calculation accuracy is high and the deviation of the results is basically within 15%, which is in good agreement with the numerical simulation results. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 7339 KiB

Open AccessArticle

Correlation between the Compressive Strength and Ultrasonic Pulse Velocity of Cement Mortars Blended with Silica Fume: An Analysis of Microstructure and Hydration Kinetics

by Geuntae Hong, Sangwoo Oh, Seongcheol Choi, Won-Jong Chin, Young-Jin Kim and Chiwon Song

Materials 2021, 14(10), 2476; https://doi.org/10.3390/ma14102476 - 11 May 2021

Cited by 27 | Viewed by 2380

Abstract

The effect of the replacement rate of silica fume (SF) on the correlation between the compressive strength and ultrasonic pulse velocity (UPV) of cement mortar was experimentally analyzed. Specimens were fabricated with different replacement rates of SF, the compressive strength and UPV were [...] Read more.

The effect of the replacement rate of silica fume (SF) on the correlation between the compressive strength and ultrasonic pulse velocity (UPV) of cement mortar was experimentally analyzed. Specimens were fabricated with different replacement rates of SF, the compressive strength and UPV were measured, and isothermal calorimetry and mercury intrusion porosimetry tests were conducted to analyze the effects of replacement on the hydration kinetics and microstructures on these properties. Field emission scanning electron microscopy analysis was performed to observe SF particles and microstructure. The substitution of SF changed the cement mortar’s hydration kinetics and microstructures, resulting in different strengths and UPVs depending on the replacement rate. The compressive strength and UPV for cement mortars blended with SF also showed a different exponential relationship depending on the SF replacement rate. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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23 pages, 9287 KiB

Open AccessArticle

Petrographic and Geotechnical Characteristics of Carbonate Aggregates from Poland and Their Correlation with the Design of Road Surface Structures

by Jerzy Trzciński, Emilia Wójcik, Mateusz Marszałek, Paweł Łukaszewski, Marek Krajewski and Stanisław Styk

Materials 2021, 14(8), 2034; https://doi.org/10.3390/ma14082034 - 18 Apr 2021

Cited by 2 | Viewed by 2066

Abstract

The paper presents the basic problem related with practical application of carbonate rocks in construction: are carbonate aggregates produced from such rocks favorable for building engineering, particularly for road design and construction? To resolve this problem, (1) the geological-engineering properties of aggregates are [...] Read more.

The paper presents the basic problem related with practical application of carbonate rocks in construction: are carbonate aggregates produced from such rocks favorable for building engineering, particularly for road design and construction? To resolve this problem, (1) the geological-engineering properties of aggregates are presented, (2) the correlation between petrographic and engineering parameters is shown, and (3) a strict correlation between the geological-engineering properties and the freezing-thawing and crushing resistance is recognized. This knowledge has allowed to assess the usefulness of asphalt concrete (AC) made from dolomite and limestone aggregates in the design and construction of road surface structures. The petrography was characterized using optical microscopy and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscope (EDS). Engineering properties were determined in accordance with European and Polish norms and guidelines. Statistical and design calculations were performed using dedicated software. The petrographic properties, and selected physical and mechanical parameters of the aggregates, were tested to show their influence on the freezing–thawing and crushing resistance. Strong functional relationships between the water adsorption, and the freezing–thawing and crushing resistance have been observed. Aggregate strength decreased after saturation with increasing concentrations of salt solutions. Calculations of AC fatigue durability and deformation allow for reducing the thickness of the road surface structure by about 20% in comparison to normative solutions. This conclusion has impact on the economy of road design and construction, and allows for a rational utilization of rock resources, which contributes to sustainable development of the construction industry. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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22 pages, 6020 KiB

Open AccessArticle

Static and Dynamic Stiffness of Reinforced Concrete Beams Strengthened with Externally Bonded CFRP Strips

by Michał Musiał, Tomasz Trapko and Jacek Grosel

Materials 2021, 14(4), 910; https://doi.org/10.3390/ma14040910 - 14 Feb 2021

Cited by 2 | Viewed by 2438

Abstract

This paper presents experimental investigations of reinforced concrete (RC) beams flexurally strengthened with carbon fiber reinforced polymer (CFRP) strips. Seven 3300 mm × 250 mm × 150 mm beams of the same design, with the tension reinforcement ratio of 1.01%, were tested. The [...] Read more.

This paper presents experimental investigations of reinforced concrete (RC) beams flexurally strengthened with carbon fiber reinforced polymer (CFRP) strips. Seven 3300 mm × 250 mm × 150 mm beams of the same design, with the tension reinforcement ratio of 1.01%, were tested. The beams differed in the way they were strengthened: one of the beams was the reference, two beams were passively strengthened as precracked (series B-I), two beams were passively strengthened as unprecracked (series B-II) and two beams were actively strengthened as unprecracked (series B-III). Moreover, the strengthening parameters differed between the particular series. The parameters were: CFRP strip cross-sectional areas (series B-I, B-II) or prestressing forces (series B-III). The beams were statically loaded, up to the assumed force value, in the three-point bending test and deflections at midspan were registered. After unloading the beams were suspended on flexible ropes (the free-free beam system) and their eigenfrequencies were measured using operational modal analysis (OMA). The static measurements (deflections) and the dynamic measurements (eigenfrequencies) were conducted for the adopted loading steps until failure. Static stiffnesses and dynamic stiffnesses were calculated on the basis of respectively the deflections and the eigenfrequencies. The qualitative and quantitative differences between the parameters are described. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 4929 KiB

Open AccessArticle

Sensitivity Analysis of Determining the Material Parameters of an Asphalt Pavement to Measurement Errors in Backcalculations

by Paweł Tutka, Roman Nagórski, Magdalena Złotowska and Marek Rudnicki

Materials 2021, 14(4), 873; https://doi.org/10.3390/ma14040873 - 11 Feb 2021

Cited by 4 | Viewed by 1801

Abstract

Nondestructive tests of road pavements are among the most widely used methods of pavement condition diagnostics. Deflections of road pavement under a known load are most commonly measured in such tests, e.g., with the use of falling weight deflectometer (FWD). Measured values allow [...] Read more.

Nondestructive tests of road pavements are among the most widely used methods of pavement condition diagnostics. Deflections of road pavement under a known load are most commonly measured in such tests, e.g., with the use of falling weight deflectometer (FWD). Measured values allow to determine the material parameters of the road structure, corresponding to the obtained results, by means of backcalculations. Among the factors that impact on the quality of results is the accuracy of deflection measurement. Deflection basins with small differences of displacement values may correspond to significantly different combinations of material parameters. Taking advantage of them for mechanistic calculations of road pavement may eventually lead to incorrect estimation of the remaining fatigue life and then inadequate selection of pavement reinforcement. This study investigated the impact of measurement errors on the change of the obtained values of stiffness moduli of flexible road pavement layers. Additionally, the influence of obtained material parameters on the values of key pavement strain, and consequently on its design fatigue life was presented. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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24 pages, 2342 KiB

Open AccessArticle

Laboratory Test to Evaluate the Resistance of Cementitious Materials to Biodeterioration in Sewer Network Conditions

by Amr Aboulela, Matthieu Peyre Lavigne, Amaury Buvignier, Marlène Fourré, Maud Schiettekatte, Tony Pons, Cédric Patapy, Orlane Robin, Mansour Bounouba, Etienne Paul and Alexandra Bertron

Materials 2021, 14(3), 686; https://doi.org/10.3390/ma14030686 - 02 Feb 2021

Cited by 8 | Viewed by 2988

Abstract

The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are [...] Read more.

The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are proven to not be representative of the actual deterioration phenomena in real sewer conditions, a biological test–named the Biogenic Acid Concrete (BAC) test–was developed at the University of Toulouse to reproduce the biological reactions involved in the process of concrete biodeterioration in sewers. The test consists in trickling a solution containing a safe reduced sulfur source onto the surface of cementitious substrates previously covered with a high diversity microbial consortium. In these conditions, a sulfur-oxidizing metabolism naturally develops in the biofilm and leads to the production of biogenic sulfuric acid on the surface of the material. The representativeness of the test in terms of deterioration mechanisms has been validated in previous studies. A wide range of cementitious materials have been exposed to the biodeterioration test during half a decade. On the basis of this large database and the expertise gained, the purpose of this paper is (i) to propose a simple and robust performance criterion for the test (standardized leached calcium as a function of sulfate produced by the biofilm), and (ii) to demonstrate the repeatability, reproducibility, and discriminability of the test method. In only a 3-month period, the test was able to highlight the differences in the performances of common cement-based materials (CEM I, CEM III, and CEM V) and special calcium aluminate cement (CAC) binders with different nature of aggregates (natural silica and synthetic calcium aluminate). The proposed performance indicator (relative standardized leached calcium) allowed the materials to be classified according to their resistance to biogenic acid attack in sewer conditions. The repeatability of the test was confirmed using three different specimens of the same material within the same experiment and the reproducibility of the results was demonstrated by standardizing the results using a reference material from 5 different test campaigns. Furthermore, developing post-testing processing and calculation methods constituted a first step toward a standardized test protocol. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 9920 KiB

Open AccessArticle

Effect of the Notch-to-Depth Ratio on the Post-Cracking Behavior of Steel-Fiber-Reinforced Concrete

by José Valdez Aguilar, César A. Juárez-Alvarado, José M. Mendoza-Rangel and Bernardo T. Terán-Torres

Materials 2021, 14(2), 445; https://doi.org/10.3390/ma14020445 - 18 Jan 2021

Cited by 5 | Viewed by 2267

Abstract

Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically [...] Read more.

Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically and experimentally the effect of the addition of the steel fibers on the performance of the post-cracking stage on fiber-reinforced concrete, by studying four notch-to-depth ratios of 0, 0.08, 0.16, and 0.33. This was evaluated through 72 bending tests, using plain concrete (control) and fiber-reinforced concrete with volume fibers of 0.25% and 0.50%. Results showed that the specimens with a notch-to-depth ratio up to 0.33 are capable of attaining a hardening behavior. The study concludes that the increase in the dosage leads to an improvement in the residual performance, even though an increase in the notch-to-depth ratio has also occurred. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 5959 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Long-Term Strength Development of Steel Fiber Shotcrete with Cast Concrete Based on Accelerator Type

by Kyong Ku Yun, Seunghak Choi, Taeho Ha, Mohammad Shakhawat Hossain and Seungyeon Han

Materials 2020, 13(24), 5599; https://doi.org/10.3390/ma13245599 - 08 Dec 2020

Cited by 7 | Viewed by 1871

Abstract

This study analyzed the effect of accelerating agents, such as aluminate, cement mineral, and alkali-free accelerators, on the long-term performance of steel-fiber-reinforced shotcrete. The shotcrete performance was studied based on the type and amount of steel fiber added. Performance tests were performed to [...] Read more.

This study analyzed the effect of accelerating agents, such as aluminate, cement mineral, and alkali-free accelerators, on the long-term performance of steel-fiber-reinforced shotcrete. The shotcrete performance was studied based on the type and amount of steel fiber added. Performance tests were performed to identify the accelerator providing better long-term performance to the steel-fiber-reinforced shotcrete. Changes in strength and flexural performance over time were investigated. The compressive strength and flexural strength tests on 1-, 3-, 6-, 12-, and 24-month-old test specimens were performed, wherein 37 kg of steel fiber was added to the cement mineral and aluminate mixes, and 40 kg of steel fiber was added to the alkali-free mix. The 1-month compressive strength result of all the test variables satisfied the Korea Expressway Corporation standard. The compressive strength of the cast concrete and shotcrete specimens increased with age, demonstrating a strength reduction, particularly in the 24-month-old shotcrete specimens. Thus, the shotcrete performance may deteriorate in the long-term. In the 24-month-old specimen, substantial flexural strength reduction was observed, particularly in the aluminate and alkali-free specimens. The relative strength of the specimens was compared with that of the cast concrete mold specimens. The results suggest the use of alkali-free accelerators, considering the long-term performance of tunnels and safety of workers. Moreover, increasing the steel fiber performance rather than the amount of low-performance steel fiber must be considered. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 8369 KiB

Open AccessArticle

Strengthening of Concrete Column by Using the Wrapper Layer of Fibre Reinforced Concrete

by Peter Koteš, Martin Vavruš, Jozef Jošt and Jozef Prokop

Materials 2020, 13(23), 5432; https://doi.org/10.3390/ma13235432 - 28 Nov 2020

Cited by 21 | Viewed by 3019

Abstract

Structures and bridges are being designed on the proposed and requested design lifetime of 50 to 100 years. In practice, one can see that the real lifetime of structures and bridges is shorter in many cases, in some special cases extremely shorter. The [...] Read more.

Structures and bridges are being designed on the proposed and requested design lifetime of 50 to 100 years. In practice, one can see that the real lifetime of structures and bridges is shorter in many cases, in some special cases extremely shorter. The reasons for the lifetime shortening can be increased of the load cases (e.g., due to traffic on bridges, or due to other uses of a structure), using the material of lower quality, implementation of new standards and codes according to Eurocode replacing older ones. During the whole lifetime the structures must be maintained to fulfil the code requests. If the constructions are not able to fulfil the Ultimate Limit States (ULS) and the Serviceability Limit State (SLS), the structures or bridges have to be strengthened (whole or its elements). The purpose of the paper is the presentation of using a layer of the fibre concrete for a columns’ strengthening. Using the fibre reinforced concrete (FRC) of higher tensile strength makes it possible to increase the load-bearing capacity of the cross-section the column. The contact between the old concrete (core of column) and newly added layer (around column) is very important for using that method of strengthening. In the article, there is also a comparison of the surface modification methods. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 2440 KiB

Open AccessArticle

Effect of Hydrophobic Treatments on Improving the Salt Frost Resistance of Concrete

by Guo Li, Chunhua Fan, Yajun Lv and Fujun Fan

Materials 2020, 13(23), 5361; https://doi.org/10.3390/ma13235361 - 26 Nov 2020

Cited by 7 | Viewed by 1740

Abstract

Hydrophobic treatment is an important method to improve the waterproof properties of concrete. To evaluate the effectiveness of hydrophobic treatments on improving the salt frost resistance of concrete, two representative commercial ordinary water repellent agents of silane and organosilicone emulsion were selected, and [...] Read more.

Hydrophobic treatment is an important method to improve the waterproof properties of concrete. To evaluate the effectiveness of hydrophobic treatments on improving the salt frost resistance of concrete, two representative commercial ordinary water repellent agents of silane and organosilicone emulsion were selected, and concrete specimens with three water/cement ratios were fabricated. After the application of repellent agents on concrete surfaces, accelerated saline (5% MgCl₂) freeze-thaw cycles were conducted on the specimens. The mass losses and relative dynamic modulus of elasticity (RDME) of concrete were tested periodically. The contact angles and water absorption ratios of concrete with and without hydrophobic treatments were also tested. Results showed that the repellent agents could substantially enhance the hydrophobicity of concrete and greatly reduce its water absorption. Different repellent agents exerted diverse improvements on concrete hydrophobicity. Meanwhile, the repellent agents could improve concrete resistance against salt scaling and RDME losses to a certain degree, and concrete with strong hydrophobicity showed relatively high salt frost resistance. However, the ordinary water repellent agents cannot achieve the same enhancement on salt frost resistance of concrete as that on the water hydrophobicity of concrete. With saline freezing and thawing cycles, the hydrophobic layer formed by the repellent agents on superficial concrete was destroyed gradually. As a result, the salt frost resistance of concrete from the hydrophobic treatments was ultimately lost. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 15297 KiB

Open AccessEditor’s ChoiceArticle

Cementitious Composites with High Compaction Potential: Modeling and Calibration

by Giao Vu, Tagir Iskhakov, Jithender J. Timothy, Christoph Schulte-Schrepping, Rolf Breitenbücher and Günther Meschke

Materials 2020, 13(21), 4989; https://doi.org/10.3390/ma13214989 - 05 Nov 2020

Cited by 13 | Viewed by 2371

Abstract

There is an increasing need for the development of novel technologies for tunnel construction in difficult geological conditions to protect segmental linings from unexpected large deformations. In the context of mechanized tunneling, one method to increase the damage tolerance of tunnel linings in [...] Read more.

There is an increasing need for the development of novel technologies for tunnel construction in difficult geological conditions to protect segmental linings from unexpected large deformations. In the context of mechanized tunneling, one method to increase the damage tolerance of tunnel linings in such conditions is the integration of a compressible two-component grout for the annular gap between the segmental linings and the deformable ground. In this regard, expanded polystyrene (EPS) lightweight concrete/mortar has received increasing interest as a potential “candidate material” for the aforementioned application. In particular, the behavior of the EPS lightweight composites can be customized by modifying their pore structure to accommodate deformations due to specific geological conditions such as squeezing rocks. To this end, novel compressible cementitious EPS-based composite materials with high compaction potential have been developed. Specimens prepared from these composites have been subjected to compressive loads with and without lateral confinement. Based on these experimental data a computational model based on the Discrete Element Method (DEM) has been calibrated and validated. The proposed calibration procedure allows for modeling and prognosis of a wide variety of composite materials with a high compaction potential. The calibration procedure is characterized by the identification of physically quantifiable parameters and the use of phenomenological submodels. Model prognoses show excellent agreement with new experimental measurements that were not incorporated in the calibration procedure. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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11 pages, 3571 KiB

Open AccessArticle

Permeabilities and Mechanical Properties of Hardened Cement Pastes Modified with Sodium Laurate and Nano Silica

by Fajun Wang and Sheng Lei

Materials 2020, 13(21), 4867; https://doi.org/10.3390/ma13214867 - 30 Oct 2020

Cited by 1 | Viewed by 1642

Abstract

In this work, a method of imparting hydrophobicity and high strength to hardened cement paste (HCP) is proposed. Sodium laurate (SL) was used as a hydrophobic modifier and nano silica (NS) as a pozzolan. The HCP was modified by SL and NS simultaneously. [...] Read more.

In this work, a method of imparting hydrophobicity and high strength to hardened cement paste (HCP) is proposed. Sodium laurate (SL) was used as a hydrophobic modifier and nano silica (NS) as a pozzolan. The HCP was modified by SL and NS simultaneously. HCP modified with different contents of SL and NS was prepared. Surface wettability, micro-structures, chemical composition, and organic structure were systematically studied using contact angle (CA) measurement, scanning electron microscope (SEM) observation, X-ray photoelectron spectroscopy (XPS), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), respectively. The surface CA of the sample is 138.5° and has high hydrophobicity. Compared with the reference sample, the water absorption of the modified sample reduced by 96.55%, while the compressive strength only reduced by 6.91%. Therefore, using hydrophobic modifier and reinforcing agent as cement admixture is an effective method to endow concrete with hydrophobicity and high strength at the same time. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 6156 KiB

Open AccessArticle

Study of Mechanical Properties of an Eco-Friendly Concrete Containing Recycled Carbon Fiber Reinforced Polymer and Recycled Aggregate

by Chen Xiong, Tianhao Lan, Qiangsheng Li, Haodao Li and Wujian Long

Materials 2020, 13(20), 4592; https://doi.org/10.3390/ma13204592 - 15 Oct 2020

Cited by 10 | Viewed by 2294

Abstract

This study investigates the feasibility of collaborative use of recycled carbon fiber reinforced polymer (RCFRP) fibers and recycled aggregate (RA) in concrete, which is called RCFRP fiber reinforced RA concrete (RFRAC). The mechanical properties of the composite were studied through experimental investigation, considering [...] Read more.

This study investigates the feasibility of collaborative use of recycled carbon fiber reinforced polymer (RCFRP) fibers and recycled aggregate (RA) in concrete, which is called RCFRP fiber reinforced RA concrete (RFRAC). The mechanical properties of the composite were studied through experimental investigation, considering different RCFRP fiber contents (0%, 0.5%, 1.0%, and 1.5% by volume) and different RA replacement rates (0%, 10%, 20%, and 30% by volume). Specifically, ten different mixes were designed to explore the flowability and compressive and flexural strengths of the proposed composite. Experimental results indicated that the addition of RCFRP fibers and RA had a relatively small influence on the compressive strength of concrete (less than 5%). Moreover, the addition of RA slightly decreased the flexural strength of concrete, while the addition of RCFRP fibers could significantly improve the flexural performance. For example, the flexural strength of RA concrete with 1.5% RCFRP fiber addition increased by 32.7%. Considering the good flexural properties of the composite and its potential in reducing waste CFRP and construction solid waste, the proposed RFRAC is promising for use in civil concrete structures with high flexural performance requirements. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 7358 KiB

Open AccessArticle

Long-Term Bonding and Tensile Strengths of Carbon Textile Reinforced Mortar

by Kira Heins, Magdalena Kimm, Lea Olbrueck, Matthias May, Thomas Gries, Annette Kolkmann, Gum-Sung Ryu, Gi-Hong Ahn and Hyeong-Yeol Kim

Materials 2020, 13(20), 4485; https://doi.org/10.3390/ma13204485 - 10 Oct 2020

Cited by 4 | Viewed by 2067

Abstract

This paper deals with the long-term bonding and tensile strengths of textile reinforced mortar (TRM) exposed to harsh environments. The objective of this study was to investigate the long-term bonding and tensile strengths of carbon TRM by an accelerated aging method. Moisture, high [...] Read more.

This paper deals with the long-term bonding and tensile strengths of textile reinforced mortar (TRM) exposed to harsh environments. The objective of this study was to investigate the long-term bonding and tensile strengths of carbon TRM by an accelerated aging method. Moisture, high temperature, and freezing–thaw cycles were considered to simulate harsh environmental conditions. Grid-type textiles were surface coated to improve the bond strength with the mortar matrix. A total of 130 TRM specimens for the bonding test were fabricated and conditioned for a prolonged time up to 180 days at varying moisture conditions and temperatures. The long-term bonding strength of TRM was evaluated by a series of bonding tests. On the other hand, a total of 96 TRM specimens were fabricated and conditioned at freezing–thaw conditions and elevated temperature. The long-term tensile strength of TRM was evaluated by a series of direct tensile tests. The results of the bonding test indicated that TRM was significantly degraded by moisture. On the other hand, the influence of the freezing–thaw conditions and high temperature on the tensile strength of the TRM was insignificant. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 3048 KiB

Open AccessArticle

Interface Shear Strength at Various Joint Types in High-Strength Precast Concrete Structures

by Young-Jin Kim, Won-Jong Chin and Se-Jin Jeon

Materials 2020, 13(19), 4364; https://doi.org/10.3390/ma13194364 - 30 Sep 2020

Cited by 8 | Viewed by 2343

Abstract

More precast concrete structures have recently been constructed due to their many advantages when compared to conventional cast-in-place construction. Structural behavior at the joints between the precast segments can significantly affect the overall integrity, safety, and serviceability of the structure. In this study, [...] Read more.

More precast concrete structures have recently been constructed due to their many advantages when compared to conventional cast-in-place construction. Structural behavior at the joints between the precast segments can significantly affect the overall integrity, safety, and serviceability of the structure. In this study, therefore, the interface shear strength of high-strength precast members was investigated by performing push-off tests with the following variables: compressive strength of precast members, dry or wet joint, number and height of shear keys, joint width, filler type, curing temperature, and lateral compressive stress. The test results were analyzed to reveal the effect of each test variable on the joint shear strengths of the specimens. For instance, the failure loads were increased by 14–140%, depending on the lateral compressive stress, as the specified compressive strength of the precast members was increased from 80 to 150 MPa in the dry joints. The failure loads of the wet joints strongly depended on the strength of the filler rather than on that of the precast members and, as a result, the specimen with ultra-high-strength concrete filler was 46–48% stronger than those with high-strength mortar filler. The shear strengths of various joint types obtained from the test were further analyzed in comparison with the predictive equations of Japan Society of Civil Engineers (JSCE) and American Association of State Highway and Transportation Officials (AASHTO) with the aim of validating the appropriateness of these design provisions. In particular, an improved value of a coefficient in the JSCE equation is proposed to cover a range of compressive strengths in various precast members and filling materials. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 2576 KiB

Open AccessArticle

Improving Recycled Aggregate Quality by Mechanical Pre-Processing

by Madumita Sadagopan, Katarina Malaga and Agnes Nagy

Materials 2020, 13(19), 4342; https://doi.org/10.3390/ma13194342 - 29 Sep 2020

Cited by 8 | Viewed by 1845

Abstract

Concrete with crushed concrete aggregates (CCA) shows lesser compressive strength than reference concrete with natural aggregates. The goal of this study is to improve the strength of structural concrete with 53% and 100% CCA replacements without increasing the cement content. Thus, improvements in [...] Read more.

Concrete with crushed concrete aggregates (CCA) shows lesser compressive strength than reference concrete with natural aggregates. The goal of this study is to improve the strength of structural concrete with 53% and 100% CCA replacements without increasing the cement content. Thus, improvements in CCA quality are induced by combining mechanical and pre-soaking pre-processing techniques. Mechanical pre-processing by rotating drum is separately pursued on fine and coarse CCA for 10 and 15 min respectively. Results show, adhered mortar content and CCA water absorption reduces as pre-processing duration increases. Pre-processing influences CCA particle grading, flakiness index, shape index, void-content, unit-weight and density, jointly seen as packing density, which increases with pre-processing duration. Water amount to pre-soak CCA before concrete mixing is stable despite grading modifications, due to reduced water absorption resulting from mechanical pre-processing. Compressive strength and workability for pre-processed CCA50 and CCA100 concrete are comparable to reference concrete and show similar trends of improvement with packing density. Packing density markedly shows the quality improvements induced by pre-processing on CCA, maybe considered as one of the quality assessment indexes for CCA. Packing density should be investigated for other recipes to see the stability of the trend with workability and compressive strength. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 26850 KiB

Open AccessArticle

Formation of Geopolymers Using Sodium Silicate Solution and Aluminum Orthophosphate

by Stephan Partschefeld, Torben Wiegand, Frank Bellmann and Andrea Osburg

Materials 2020, 13(18), 4202; https://doi.org/10.3390/ma13184202 - 21 Sep 2020

Cited by 6 | Viewed by 3648

Abstract

This paper reports the formation and structure of fast setting geopolymers activated by using three sodium silicate solutions with different modules (1.6, 2.0 and 2.4) and a berlinite-type aluminum orthophosphate. By varying the concentration of the aluminum orthophosphate, different Si/Al-ratios were established (6, [...] Read more.

This paper reports the formation and structure of fast setting geopolymers activated by using three sodium silicate solutions with different modules (1.6, 2.0 and 2.4) and a berlinite-type aluminum orthophosphate. By varying the concentration of the aluminum orthophosphate, different Si/Al-ratios were established (6, 3 and 2). Reaction kinetics of binders were determined by isothermal calorimetric measurements at 20 °C. X-ray diffraction analysis as well as nuclear magnetic resonance (NMR) measurements were performed on binders to determine differences in structure by varying the alkalinity of the sodium silicate solutions and the Si/Al-ratio. The calorimetric results indicated that the higher the alkalinity of the sodium silicate solution, the higher the solubility and degree of conversion of the aluminum orthophosphate. The results of X-ray diffraction and Rietveldt analysis, as well as the NMR measurements, confirmed the assumption of the calorimetric experiments that first the aluminum orthophosphate was dissolved and then a polycondensation to an amorphous aluminosilicate network occurred. The different amounts of amorphous phases formed as a function of the alkalinity of the sodium silicate solution, indicate that tetrahydroxoaluminate species were formed during the dissolution of the aluminum orthophosphate, which reduce the pH value. This led to no further dissolution of the aluminum orthophosphate, which remained unreacted. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 4534 KiB

Open AccessArticle

A New Approach for Designing Fluid Concrete with Low Cement Content: Optimization of Packing Density of Aggregates

by Ning Zhang, Wenqiang Zuo, Wen Xu and Shenyou Song

Materials 2020, 13(18), 4082; https://doi.org/10.3390/ma13184082 - 14 Sep 2020

Cited by 1 | Viewed by 1872

Abstract

The current study aims at proposing a novel and simple method for designing fluid concrete such as self-compacting concrete (SCC) with a low cementitious binder content to reduce the carbon footprint. Different testing methods regarding the packing density of aggregate mixtures are performed [...] Read more.

The current study aims at proposing a novel and simple method for designing fluid concrete such as self-compacting concrete (SCC) with a low cementitious binder content to reduce the carbon footprint. Different testing methods regarding the packing density of aggregate mixtures are performed and compared. The W/C was determined according to the target compression strength. Slump flow spread is carried out to determine the most appropriate superplasticizer (SP) dosage and aggregate volume fractions and proportions in concrete mixtures. Furthermore, hardened performance, including compression strength and drying shrinkage of the fluid concrete, are characterized. Finally, a mix design process of fluid concrete with low cement content was proposed based on the preferred fresh and hardened properties of the concrete mixtures. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 3339 KiB

Open AccessArticle

Study of In Situ Foamed Fly Ash Geopolymer

by Zijian Su, Wei Hou, Zengqing Sun and Wei Lv

Materials 2020, 13(18), 4059; https://doi.org/10.3390/ma13184059 - 12 Sep 2020

Cited by 12 | Viewed by 2276

Abstract

Foamed fly ash geopolymer was synthesized in this work to produce geopolymeric lightweight concrete (GLWC). Fly ash was activated by sodium silicate solution, and aluminum powder was employed as an in situ chemical foaming agent. The synthesized pastes were cured at 40 °C [...] Read more.

Foamed fly ash geopolymer was synthesized in this work to produce geopolymeric lightweight concrete (GLWC). Fly ash was activated by sodium silicate solution, and aluminum powder was employed as an in situ chemical foaming agent. The synthesized pastes were cured at 40 °C for 28 days, with bulk densities of resultant GLWCs ranging from 600 to 1600 kg/m³. The resulting mechanical properties, thermal conductivity, microstructure, and reaction product were fully characterized. Results show that GLWC had higher mechanical strength than commercial aerated concrete and developed 80–90% of its corresponding 28 days strength after curing for 7 days. For densities from 1200 to 600 kg/m³, the thermal conductivity diminished from 0.70 to 0.22 W/mK, which is much better than that of its counterpart, ordinary Portland cement (OPC). Scanning electron microscopy (SEM) images revealed decent matrices comprising geopolymeric gel and unreacted fly ash. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 7125 KiB

Open AccessArticle

The Effect of the Type and Amount of Synthetic Fibers on the Effectiveness of Dispersed Reinforcement in Soil-Cements

by Krystian Brasse, Tomasz Tracz and Tomasz Zdeb

Materials 2020, 13(18), 3917; https://doi.org/10.3390/ma13183917 - 04 Sep 2020

Cited by 6 | Viewed by 1905

Abstract

The paper deals with mechanical properties of soil-cement composites made with non-cohesive soil and reinforced with dispersed fibers. The research was carried out on the basis of three soil-cement matrices whose compositions varied in terms of the volumetric fraction of cement paste and [...] Read more.

The paper deals with mechanical properties of soil-cement composites made with non-cohesive soil and reinforced with dispersed fibers. The research was carried out on the basis of three soil-cement matrices whose compositions varied in terms of the volumetric fraction of cement paste and the water-cement ratio. Two types of polypropylene fibers were used as dispersed reinforcement: single fibrillated-tapes polypropylene fibers (SFPF) and bundles of coiled fibrillated-tapes polypropylene fibers (BCFPF). The fibers varied in terms of their length and mass fraction. The objective of the study was to assess the effect of the addition of fibers to soil-cement composites on their flexural tensile strength and on their behavior in the post-critical state. The studies were carried out after 28 days of curing. Bending tests were carried out to determine post-critical stress values σ_CMODi, stress values at which the matrix is destroyed (limit of proportionality) σ_LOP, maximum stress values transferred by the fibers σ_MOR (modulus of rupture), and total fracture energy G_f,tot as well as compressive strength. The test results obtained, and their analysis, indicate the significant impact of the dispersed reinforcement used on the performance of such composites during bending. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 7021 KiB

Open AccessFeature PaperArticle

Influence of Crack Width on Chloride Penetration in Concrete Subjected to Alternating Wetting–Drying Cycles

by Jun Lai, Jian Cai, Qing-Jun Chen, An He and Mu-Yang Wei

Materials 2020, 13(17), 3801; https://doi.org/10.3390/ma13173801 - 28 Aug 2020

Cited by 12 | Viewed by 2135

Abstract

To investigate the durability of reinforced concrete (RC) beams under the combined actions of transverse cracks and corrosion, corrosion tests were conducted on a total of eight RC beams with different water–cement ratios and cracking states. The effects of the transverse crack width, [...] Read more.

To investigate the durability of reinforced concrete (RC) beams under the combined actions of transverse cracks and corrosion, corrosion tests were conducted on a total of eight RC beams with different water–cement ratios and cracking states. The effects of the transverse crack width, water–cement ratio, and the length of the wetting–drying cycle on the distribution of the free chloride concentration, the cross-sectional loss of the tensile steel bars, and the chloride diffusion coefficient are analyzed. The results show that the widths of the transverse crack and the water–cement ratio of concrete greatly affected the chloride profile and content of the RC beam specimens. Specifically, the chloride contents in all the cracked RC beams at the depth of the steel bar exceeded the threshold value of 0.15%. As the width of the cracks increased, the chloride concentration and penetration of the cracked concrete beam increased. However, the chloride concentration at the reinforcement position did not seem to be obviously affected by increasing the wetting–drying cycles from 182 days to 364 days. Moreover, the decrease of the water–cement ratio effectively inhibited the penetration of chloride ions in the RC beam specimens. In terms of the cross-sectional loss of the steel bars, the average loss of the steel bar increases with increasing crack width for the beams with 182-day cycles, while the effect of crack width on the average loss is not as noticeable for the beams with 364-day cycles. Finally, a model is proposed to predict the relationship between the crack width influence coefficient, μ, and the crack width, w, and this model shows good agreement with the experimental results. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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28 pages, 6830 KiB

Open AccessArticle

Biological Self-Healing of Cement Paste and Mortar by Non-Ureolytic Bacteria Encapsulated in Alginate Hydrogel Capsules

by Mohammad Fahimizadeh, Ayesha Diane Abeyratne, Lee Sui Mae, R. K. Raman Singh and Pooria Pasbakhsh

Materials 2020, 13(17), 3711; https://doi.org/10.3390/ma13173711 - 22 Aug 2020

Cited by 32 | Viewed by 4758

Abstract

Crack formation in concrete is one of the main reasons for concrete degradation. Calcium alginate capsules containing biological self-healing agents for cementitious materials were studied for the self-healing of cement paste and mortars through in vitro characterizations such as healing agent survivability and [...] Read more.

Crack formation in concrete is one of the main reasons for concrete degradation. Calcium alginate capsules containing biological self-healing agents for cementitious materials were studied for the self-healing of cement paste and mortars through in vitro characterizations such as healing agent survivability and retention, material stability, and biomineralization, followed by in situ self-healing observation in pre-cracked cement paste and mortar specimens. Our results showed that bacterial spores fully survived the encapsulation process and would not leach out during cement mixing. Encapsulated bacteria precipitated CaCO₃ when exposed to water, oxygen, and calcium under alkaline conditions by releasing CO₃²⁻ ions into the cement environment. Capsule rupture is not required for the initiation of the healing process, but exposure to the right conditions are. After 56 days of wet–dry cycles, the capsules resulted in flexural strength regain as high as 39.6% for the cement mortar and 32.5% for the cement paste specimens. Full crack closure was observed at 28 days for cement mortars with the healing agents. The self-healing system acted as a biological CO₃²⁻ pump that can keep the bio-agents retained, protected, and active for up to 56 days of wet-dry incubation. This promising self-healing strategy requires further research and optimization. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 5925 KiB

Open AccessArticle

Experimental Study of the Relaxation Properties of Carbon Fiber Cloth

by Qiang Wang, Hua-Lin Song, Chun-Ling Lu, Wan-Xu Zhu and Jia-Zhu Huang

Materials 2020, 13(16), 3603; https://doi.org/10.3390/ma13163603 - 14 Aug 2020

Cited by 2 | Viewed by 1708

Abstract

In this study, a new method was proposed to study the relaxation properties of carbon fiber reinforced plastics (CFRP) fabric under axial tension. Under the condition of constant temperature and humidity, six groups of 168 h stress relaxation tests were conducted. Considering the [...] Read more.

In this study, a new method was proposed to study the relaxation properties of carbon fiber reinforced plastics (CFRP) fabric under axial tension. Under the condition of constant temperature and humidity, six groups of 168 h stress relaxation tests were conducted. Considering the influence of the prestress level, the size of CFRP cloth, and the surface coating of CFRP cloth on the relaxation performance, the measures to reduce the relaxation loss were proposed. The relaxation rate calculation model was established based on the test results of the authors and other scholars and was validated through comparisons with the test results. The results indicate that the relaxation rate of CFRP cloth was between 1.92% and 6.1%. When the prestress level was smaller than 0.3 fu, the relaxation rate of CFRP cloth decreased with the increase of prestress level. When the prestress level was greater than 0.3 fu, the relaxation rate increased with the increase of the prestress level. Under the same conditions, the relaxation rate of the CFRP specimens coated with glue was smaller than the uncoated samples by 3.21–6.28%. The calculation model could well estimate the relaxation rate of CFRP cloth. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 2472 KiB

Open AccessArticle

Study of the Air-Entraining Behavior Based on the Interactions between Cement Particles and Selected Cationic, Anionic and Nonionic Surfactants

by Qi Liu, Zhitao Chen and Yingzi Yang

Materials 2020, 13(16), 3514; https://doi.org/10.3390/ma13163514 - 09 Aug 2020

Cited by 24 | Viewed by 3090

Abstract

The essential role of the air void size distribution in air-entrained cementitious materials is widely accepted. However, how the air-entraining behavior is affected by features such as the molecular structure of air-entraining agents (AEAs), the type of solid particles, or the chemical environment [...] Read more.

The essential role of the air void size distribution in air-entrained cementitious materials is widely accepted. However, how the air-entraining behavior is affected by features such as the molecular structure of air-entraining agents (AEAs), the type of solid particles, or the chemical environment of the pore solution in fresh mortars is still not well understood. Besides, methods to assess the interaction between AEAs and cement particles are limited. Thus, in this study, the air-entraining behaviors of three kinds of surfactant (cationic, anionic, and nonionic) were examined. The general working mechanisms of these surfactants were studied by zeta potential and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Results indicate that the cationic surfactant entrains improper coarse air voids due to the strong electrical interaction between air bubbles formed by the cationic surfactant and negatively charged cement particles. The anionic surfactant interacts with the positively charged part of cement particles, and thus entrains finer air voids. The interaction between the nonionic surfactant and cement particles is very weak; as a result, the nonionic surfactant entrains the finest and homogeneous air voids. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 5319 KiB

Open AccessArticle

Torsional Behaviour of Steel Fibre Reinforced Alkali Activated Concrete

by Chee Keong Lau, Trevor N. S. Htut, Jack J. Melling, Amin Chegenizadeh and Tian Sing Ng

Materials 2020, 13(15), 3423; https://doi.org/10.3390/ma13153423 - 03 Aug 2020

Cited by 4 | Viewed by 3020

Abstract

Nine alkali-activated concrete beams were produced and tested under pure torsional load to failure. The alkali-activated concrete beams were produced with following variables: (i) fibres only, (ii) conventionally reinforced or (iii) a hybrid of both fibres and conventional steel reinforcement. The fibres only [...] Read more.

Nine alkali-activated concrete beams were produced and tested under pure torsional load to failure. The alkali-activated concrete beams were produced with following variables: (i) fibres only, (ii) conventionally reinforced or (iii) a hybrid of both fibres and conventional steel reinforcement. The fibres only beams were found to have approximately 20% higher cracking torque than conventionally reinforced beams. However, fibres only beams were observed to have lower post crack ductility and inconsistent post crack behaviour, in comparison to conventionally reinforced alkali-activated concrete (AAC) beams. On the other hand, the hybrid reinforcements in AAC beams were found to demonstrate more ductile post crack behaviour consistently of the beams tested. Hybrid reinforcement was also shown to have 20% and 25% improvement in cracking and ultimate torque compared to conventionally reinforced, which suggests that it is suitable for industrial applications to improve structure capacity. The ultimate torque results of the beams were compared to an analytical model that considered the contribution of fibres. It was found that the ultimate torque of the hybrid reinforced beam has good correlation with the model but overestimated conventionally reinforced beams. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 4043 KiB

Open AccessArticle

A Systematic Study on Polymer-Modified Alkali-Activated Slag–Part II: From Hydration to Mechanical Properties

by Zichen Lu, Jan-Philip Merkl, Maxim Pulkin, Rafia Firdous, Steffen Wache and Dietmar Stephan

Materials 2020, 13(15), 3418; https://doi.org/10.3390/ma13153418 - 03 Aug 2020

Cited by 9 | Viewed by 2413

Abstract

The effect of styrene-acrylate (SA) polymer latex on alkali-activated slag (AAS) was systematically studied in the aspects of hydration, hydration products, pore structure and mechanical properties through the combined analytical techniques including calorimetry, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and mechanical measurement. [...] Read more.

The effect of styrene-acrylate (SA) polymer latex on alkali-activated slag (AAS) was systematically studied in the aspects of hydration, hydration products, pore structure and mechanical properties through the combined analytical techniques including calorimetry, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and mechanical measurement. It was found that the addition of SA does not retard the AAS hydration, but slightly accelerates it, possibly due to the increasing ion diffusion through the loosely structured hydration products. Pore structure analysis indicates that the addition of polymer increases the cumulative pore volume and the portion of pores with size >100 nm in the hardened AAS paste. The addition of SA latex results in a continuous decrease of the compressive strength, but the flexural strength firstly increases and then decreases with the increase of polymer dosage. The polymer dosage of 2.5 wt % is optimal when applying polymer latex in the AAS system in this study. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 3264 KiB

Open AccessArticle

A Mathematical Model for the Electrical Resistivity of Cement Paste at Early Ages Considering the Partially Saturated State

by Ye Tian, Xin Xu, Haodong Ji, Zushi Tian, Xianyu Jin, Nanguo Jin, Dongming Yan and Shengwen Tang

Materials 2020, 13(15), 3306; https://doi.org/10.3390/ma13153306 - 24 Jul 2020

Cited by 2 | Viewed by 1965

Abstract

For cementitious materials, electrical resistivity is often used in the study of the cement hydration process at early age, as one of the few indicators that can be continuously and non-destructively monitored. Variation characteristics of resistivity are widely reported to interact with the [...] Read more.

For cementitious materials, electrical resistivity is often used in the study of the cement hydration process at early age, as one of the few indicators that can be continuously and non-destructively monitored. Variation characteristics of resistivity are widely reported to interact with the early-age performance of cement paste, such as hydration kinetics parameters and setting time. However, there is no reasonable mathematical model to predict the resistivity at early ages, especially within the first 24 h, due to significant changes in the porosity and degree of saturation. In this work, a mathematical model was developed by considering the partially saturated state and density change of C-S-H (calcium silicate hydrate). To verify the model, two experimental methods were chosen, including the non-contact electrical resistivity test and isothermal calorimetry test. The hydration heat and resistivity of cement paste with a water–cement ratio of 0.35 and 0.45 were continuously monitored for 3 days. In the resistivity test, embedded temperature sensors were used to monitor the internal temperature and temperature correction was treated carefully in order to obtain accurate data. The test results prove that the mathematical model can accurately predict electrical resistivity and describe the saturation state of early-age cement pastes under sealed curing. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 5155 KiB

Open AccessArticle

Comparison Study on the Adsorption Behavior of Chemically Functionalized Graphene Oxide and Graphene Oxide on Cement

by Min Wang and Hao Yao

Materials 2020, 13(15), 3274; https://doi.org/10.3390/ma13153274 - 23 Jul 2020

Cited by 7 | Viewed by 1922

Abstract

Chemical functionalization of graphene oxide (GO) is one kind of advanced strategy to eliminate the negative effects on the flowability of cement with GO. The adsorption behavior of admixture on cement plays a vital role in the flowability of cement-based materials. Herein, the [...] Read more.

Chemical functionalization of graphene oxide (GO) is one kind of advanced strategy to eliminate the negative effects on the flowability of cement with GO. The adsorption behavior of admixture on cement plays a vital role in the flowability of cement-based materials. Herein, the comparison study on the adsorption behavior (including adsorption amount, adsorption kinetics, adsorption isotherms and adsorption layer thickness) of three kinds of chemically functionalized graphene oxides (CFGOs) with different polyether amine branched-chain lengths and GO on cement is reported. The results of CFGOs and GO adsorption data on cement particles were all best fitted with the pseudo-second-order kinetic model, and also conformed to the Freundlich isothermal model, indicating that the adsorption of CFGOs and GO on cement both were multilayer type and took place in a heterogeneous manner. The adsorption of CFGOs and GO on cement was not just physical adsorption, but also engaged chemical adsorption. In contrast to GO, the adsorption behavior of CFGOs on cement represented a lesser adsorption amount, weaker adsorption capacity and thinner adsorption layer thickness. Moreover, the longer the branched-chain length of CFGOs, the greater the decreasing degrees of adsorption amount, adsorption capacity and adsorption layer thickness. Due to the consumption of the carboxyl group (-COOH) by chemical functionalization, the anchoring effect of CFGOs was weaker than GO, and the steric hindrance effect generated from branched-chains which weakened the van der Waals forces among CFGOs layers. Moreover, the steric hindrance effect strengthened with the increasing branched-chain length, thus preventing the cement particles from aggregation, which resulted in satisfactory flowability of CFGOs with incorporation of cement rather than GO. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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12 pages, 6143 KiB

Open AccessArticle

Mechanical Performance of Steel Slag Concrete under Biaxial Compression

by Xiaoyan Wen, Jingkai Zhou, Beiquan Chen, Zhiheng Deng and Bing Liu

Materials 2020, 13(15), 3268; https://doi.org/10.3390/ma13153268 - 23 Jul 2020

Cited by 3 | Viewed by 1770

Abstract

The mechanical performance of steel slag concrete (SSC) under biaxial compression is investigated by a servo-controlled static-dynamic true triaxial machine (TAWZ-5000/3000). Three replacement ratios of steel slags and four kinds of stress ratio (0.25:1, 0.5:1, 0.75:1, and 1:1) are examined in this study. [...] Read more.

The mechanical performance of steel slag concrete (SSC) under biaxial compression is investigated by a servo-controlled static-dynamic true triaxial machine (TAWZ-5000/3000). Three replacement ratios of steel slags and four kinds of stress ratio (0.25:1, 0.5:1, 0.75:1, and 1:1) are examined in this study. According to the test results, the influences of replacement ratio and stress ratio on the strength, deformation properties, stress–strain curves, and failure mode of SSC are analyzed. The results show that the failure mode of SSC under biaxial compression is plate-splitting crack. Both the strength and deformation of SSC are larger than the corresponding values of the uniaxial compression. Under the same stress ratio, the value of principal stress

σ_{3 f}

increases first and then decreases with the increase in the replacement ratio. Under the same replacement ratio,

σ_{3 f}

increases first and then decreases as the stress ratio increases, and the maximum of

σ_{3 f}

is obtained at the stress ratio of

α =

0.5:1. Based on the analysis and test data, the strength failure criterion of SSC under biaxial compression stresses is proposed. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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12 pages, 8734 KiB

Open AccessArticle

Study on the Compressive Properties of Magnesium Phosphate Cement Mixing with Eco-Friendly Coir Fiber Considering Fiber Length

by Zuqian Jiang, Liwen Zhang, Tao Geng, Yushan Lai, Weile Zheng and Min Huang

Materials 2020, 13(14), 3194; https://doi.org/10.3390/ma13143194 - 17 Jul 2020

Cited by 17 | Viewed by 2118

Abstract

Coir fiber (CF), an eco-friendly and renewable natural fiber, was introduced into magnesium phosphate cement (MPC) mortar to improve its crack resistance. A total of 21 specimens were employed to investigate the failure pattern, compressive strength, stress–strain curve, and energy absorption of MPC [...] Read more.

Coir fiber (CF), an eco-friendly and renewable natural fiber, was introduced into magnesium phosphate cement (MPC) mortar to improve its crack resistance. A total of 21 specimens were employed to investigate the failure pattern, compressive strength, stress–strain curve, and energy absorption of MPC with varying CF lengths (0, 5, 10, 15, 20, 25, and 30 mm) after a curing period of 28 days through a static compressive test. The results demonstrated that compressive strength, elastic modulus, and secant modulus decreased with the increase in CF length. However, energy absorption presented a convex curve, which increased to the maximum value (77.0% relative to the value of the specimen without CF) with a CF length of 20 mm and then declined. A series of modern micro-tests were then carried out to analyze the microstructure and composition of specimens to explain the properties microscopically. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 4622 KiB

Open AccessArticle

Mechanical Properties of Natural Fiber Reinforced Foamed Concrete

by Joaquin F. Castillo-Lara, Emmanuel A. Flores-Johnson, Alex Valadez-Gonzalez, Pedro J. Herrera-Franco, Jose G. Carrillo, P. I. Gonzalez-Chi and Q. M. Li

Materials 2020, 13(14), 3060; https://doi.org/10.3390/ma13143060 - 08 Jul 2020

Cited by 67 | Viewed by 6718

Abstract

The mechanical characterization of plain foamed concrete (PFC) and fiber-reinforced foamed concrete (FRFC) with a density of 700 kg/m³ was performed with compression and tension tests. FRFC was reinforced with the natural fiber henequen (untreated or alkaline-treated) at volume fractions of 0.5%, [...] Read more.

The mechanical characterization of plain foamed concrete (PFC) and fiber-reinforced foamed concrete (FRFC) with a density of 700 kg/m³ was performed with compression and tension tests. FRFC was reinforced with the natural fiber henequen (untreated or alkaline-treated) at volume fractions of 0.5%, 1% and 1.5%. Polypropylene fiber reinforcement was also used as a reference. For all FRFCs, the inclusion of the fibers enhanced the compressive and tensile strengths and plastic behavior, which was attributed to the increase of specimen integrity. Under compressive loading, after the peak strength, there was no considerable loss in strength and a plateau-like regime was observed. Under tensile loading, the fibers significantly increased the tensile strength of the FRFCs and prevented a sudden failure of the specimens, which was in contrast to the brittle behavior of the PFC. The tensile behavior enhancement was higher when treated henequen fibers were used, which was attributed to the increase in the fiber–matrix bond produced by the alkaline treatment. The microscopic characterization showed that the inclusion of fibers did not modify the air-void size and its distribution. Higher energy absorption was observed for FRFCs when compared to the PFC, which was attributed to the enhanced toughness and ductility by the fibers. The results presented herein warrant further research of FRFC with natural henequen fibers for engineering applications. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 6006 KiB

Open AccessArticle

Experimental Study on Mechanical and Functional Properties of Reduced Graphene Oxide/Cement Composites

by Ning Zhang, Wei She, Fengyin Du and Kaili Xu

Materials 2020, 13(13), 3015; https://doi.org/10.3390/ma13133015 - 06 Jul 2020

Cited by 33 | Viewed by 2706

Abstract

This study develops a novel self-sensing cement composite by simply mixing reduced graphene oxide (rGO) in cementitious material. The experimental results indicate that, owing to the excellent dispersion method, the nucleation and two-dimensional morphological effect of rGO optimizes the microstructure inside cement-based material. [...] Read more.

This study develops a novel self-sensing cement composite by simply mixing reduced graphene oxide (rGO) in cementitious material. The experimental results indicate that, owing to the excellent dispersion method, the nucleation and two-dimensional morphological effect of rGO optimizes the microstructure inside cement-based material. This would increase the electric conductivity, thermal property and self-induction system of cement material, making it much easier for cementitious material to better warn about impending damage. The use of rGO can improve the electric conductivity and electric shielding property of rGO-paste by 23% and 45%. The remarkable enhancement was that the voltage change rate of 1.00 wt.%-rGO paste under six-cycle loads increased from 4% to 12.6%, with strain sensitivity up to 363.10, without compromising the mechanical properties. The maximum compressive strength of the rGO-mortar can be increased from 55 MPa to 71 MPa. In conclusion, the research findings provide an effective strategy to functionalize cement materials by mixing rGO and to achieve the stronger electric shielding property and higher-pressure sensitivity of rGO–cement composites, leading to the development of a novel high strength self-sensing cement material with a flexural strength up to 49%. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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22 pages, 6927 KiB

Open AccessArticle

Estimation of Viscosity and Yield Stress of Cement Grouts at True Ground Temperatures Based on the Flow Spread Test

by Zhipeng Xu, Yichen Miao, Haikuan Wu, Xun Yuan and Changwu Liu

Materials 2020, 13(13), 2939; https://doi.org/10.3390/ma13132939 - 30 Jun 2020

Cited by 9 | Viewed by 2648

Abstract

The rheology of cement grouts often plays a crucial role in the success of rock grouting. In practice, the rheological parameters should be timely adjusted according to the evolution of grouting pressure, flow rate and injection time. However, obtaining the magnitude of rheological [...] Read more.

The rheology of cement grouts often plays a crucial role in the success of rock grouting. In practice, the rheological parameters should be timely adjusted according to the evolution of grouting pressure, flow rate and injection time. However, obtaining the magnitude of rheological parameters is not easy to achieve under site conditions. More importantly, the ground temperature in deep rock masses is elevated higher than that on the surface or under room conditions, which has been demonstrated to strongly influence the rheological properties of grouts. Reasonable understanding and control of the rheological behavior of cement grouts at true ground temperatures is very important to the quality of grouting. This paper aims to propose a simplified method to approximately estimate the initial yield stress and viscosity of cement grouts for rock grouting under elevated ground temperature that actually exists in deep rock masses, on the basis of the flow spread test. The temperature investigated was controlled between 12 °C and 45 °C to simulate the true ground temperature in rock masses with a maximum depth of 1500 m below the surface. Taking the influences of elevated temperatures into account, a temperature-based model for estimating the initial viscosity of cement grout was successfully developed on the basis of Liu’s model and the results of the flow spread test. However, the yield stress failed to be estimated by the Lapasin model due to the absence of plastic behavior of cement grouts. In contrast, yield stress can be linearly correlated to the measured relative flow area. In this work, it was also found that the dependence of yield stress of cement grouts on relative flow area is a strongly exponential law. The temperature dependence of the viscosity of water was accounted for in both estimations of viscosity and yield stress of grouts. Significantly, it was found that the packing density of cement is dependent on the grout temperature, especially when the temperature is up to 45 °C. The proposed method in this work offers an alternative solution for technicians to reasonably control the rheological properties in the increasing applications of deep rock grouting. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 7775 KiB

Open AccessArticle

Development of Self-Healing Cement Slurry through the Incorporation of Dual-Encapsulated Polyacrylamide for the Prevention of Water Ingress in Oil Well

by G. Richhariya, D.T.K. Dora, K.R. Parmar, K.K. Pant, N. Singhal, K. Lal and P.P. Kundu

Materials 2020, 13(13), 2921; https://doi.org/10.3390/ma13132921 - 29 Jun 2020

Cited by 16 | Viewed by 2955

Abstract

In the present work, a novel cross-linked polymer was synthesized though the anionic polymerization of cyanoacrylate with moisture as an initiator, methylene-bis-acrylamide as a cross-linker, and linseed oil as a spacer. Two layers of the synthesized polymer was coated over polyacrylamide for its [...] Read more.

In the present work, a novel cross-linked polymer was synthesized though the anionic polymerization of cyanoacrylate with moisture as an initiator, methylene-bis-acrylamide as a cross-linker, and linseed oil as a spacer. Two layers of the synthesized polymer was coated over polyacrylamide for its homogenous impregnation in Class-G cement slurry for the synthesis of cement core. Fourier Transformation Infrared spectroscopy and X-Ray diffraction spectrum of the synthesized polymer and cement core were obtained to investigate the presence of different functional groups and phases. Moreover, the morphologies of the dual-encapsulated polyacrylamide was observed through scanning electron microscopy. Furthermore, the water-absorption capacity of the synthesized dual-encapsulated polyacrylamide in normal and saline conditions were tested. A cement core impregnated with 16% of dosage of dual-encapsulated polyacrylamide possesses an effective self-healing capability during the water-flow test. Moreover, the maximum linear expansion of the cement core was observed to be 26%. Thus, the impregnation of dual-encapsulated polyacrylamide in cement slurry can exhibit a superior self-healing behavior upon water absorption in an oil well. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 5033 KiB

Open AccessArticle

Experimental Behavior of Cracked Reinforced Concrete Columns Strengthened with Reinforced Concrete Jacketing

by Ahmed Mohamed Sayed, Mohamed Mohamed Rashwan and Mohamed Emad Helmy

Materials 2020, 13(12), 2832; https://doi.org/10.3390/ma13122832 - 24 Jun 2020

Cited by 17 | Viewed by 2710

Abstract

Reinforced concrete (RC) columns often need to be strengthened or rehabilitated to allow them to carry the loads applied to them. In previous studies, RC columns have been strengthened by jacketing, without considering the occurrence of cracking. In this study, the behavior of [...] Read more.

Reinforced concrete (RC) columns often need to be strengthened or rehabilitated to allow them to carry the loads applied to them. In previous studies, RC columns have been strengthened by jacketing, without considering the occurrence of cracking. In this study, the behavior of RC columns strengthened externally by jacketing after cracking is analyzed. The accuracy of the existing models was verified by analyzing the performance of fifteen RC columns with different cross-sections to determine the effect of new variables, such as the column size, amount of steel reinforcement, and whether the column was cracked or not, on the effectiveness of strengthening. The analysis demonstrated that this strengthening technique could effectively improve both the ductility and strength of RC column cross-sections. The results indicate that the model suggested by the ACI-318 code can predict the ultimate load capacity of RC columns without strengthening, or strengthened by RC jacketing before or after cracking, with higher accuracy and material efficiency. The RC columns without strengthening met the safety limit of the ACI-318 model. However, for strengthened columns, a reduction coefficient must be used to enable the columns to meet the safety limit, with values of 94% and 76% for columns strengthened before and after cracking, respectively. Furthermore, strengthening after cracking affects the ultimate load capacity of the column, with 15.7%, 14.1%, and 13.5% lower loads for square, rectangular, and circular columns than those strengthened before cracking, respectively. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 6579 KiB

Open AccessArticle

The Impact of Surface Preparation for Self-Compacting, High-Performance, Fiber-Reinforced Concrete Confined with CFRP Using a Cement Matrix

by Krzysztof Adam Ostrowski, Roman Kinasz and Piotr Dybeł

Materials 2020, 13(12), 2830; https://doi.org/10.3390/ma13122830 - 24 Jun 2020

Cited by 4 | Viewed by 2061

Abstract

With the development of concrete technology, the tendency to combine different materials with each other to achieve a greater efficiency and durability of structures can be observed. In the modern construction industry, various materials and techniques are increasingly being combined in order to [...] Read more.

With the development of concrete technology, the tendency to combine different materials with each other to achieve a greater efficiency and durability of structures can be observed. In the modern construction industry, various materials and techniques are increasingly being combined in order to achieve e.g., an increased resistance to dynamic impacts of a structure, or an increased scope of work of a selected constructional element, which translates into a significant increase in the energy of destruction. Thus, hybrid elements, known as composite ones, are created, which consist of concrete and reinforcements. This study examined the influence of the preparation of the concrete surface on the behavior of high-performance, self-compacting, fiber-reinforced concrete (HPSCFRC), reinforced with carbon fibers (CF) using a cement matrix. In the general lamination processes, this is preformed using epoxy resin. However, epoxy resin is sensitive to relatively low temperatures, and therefore the authors attempted to use a cement matrix in the lamination process. When connecting hardened concrete with a fresh concrete matrix or mixture, the type of the concrete surface is significant. In this research, three types of concrete surfaces e.g., unprepared, sanded and grinded were considered. All of the surfaces were examined using a 3D laser scanner, to determine the Abbott-Firestone profile material share curve. In this research, cylindrical concrete specimens were reinforced with one, two and three layers of laminates. They were then subjected to a uniaxial compressive test. The results of tests showed that the use of cement matrix in the lamination process, due to its low efficiency, should not be applied when reinforcing concrete elements with a high compressive strength. Moreover, the grinded surface of concrete showed the best cooperation with CF reinforcement. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 4222 KiB

Open AccessArticle

Experimental Investigation of Material Properties and Self-Healing Ability in a Blended Cement Mortar with Blast Furnace Slag

by Seunghyun Na, Wenyan Zhang, Madoka Taniguchi, Nguyen Xuan Quy and Yukio Hama

Materials 2020, 13(11), 2564; https://doi.org/10.3390/ma13112564 - 04 Jun 2020

Cited by 2 | Viewed by 1853

Abstract

This paper presents the results of an experimental investigation on the material properties and self-healing ability of a blended cement mortar incorporating blast furnace slag (BFS). The effect of different types and Blaine fineness of BFS on the material properties and self-healing was [...] Read more.

This paper presents the results of an experimental investigation on the material properties and self-healing ability of a blended cement mortar incorporating blast furnace slag (BFS). The effect of different types and Blaine fineness of BFS on the material properties and self-healing was investigated. Thirteen cement mixtures with BFS of different types and degrees of Blaine fineness are tested to evaluate the mechanical properties, namely compressive strength, bending strength, freeze–thaw, and accelerated carbonation. The pore structure is examined by means of mercury intrusion porosimetry. Seven blended mortar mixtures incorporating BFS for cement are used to evaluate the mechanical properties after applying freeze–thaw cycles until the relative dynamic modulus of elasticity reached 60%. The experimental results reveal that incorporating BFS improves the mechanical properties and self-healing ability. In the investigation of self-healing, smaller particle and high replacement ratios of BFS contribute to increasing the relative dynamic modulus of elasticity and decreasing the carbonation coefficient in the mortar after re-water curing. Moreover, BFS’s larger particles and high replacement ratio are found to provide better self-healing ability. A regression equation is created to predict the relative dynamic modulus of elasticity in mortar considering the Blaine fineness, BFS replacement ratio, and curing conditions. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 13175 KiB

Open AccessArticle

Shaking Table Test of U-Shaped Walls Made of Fiber-Reinforced Foamed Concrete

by Emmanuel A. Flores-Johnson, Brenda A. Company-Rodríguez, J. Francisco Koh-Dzul and Jose G. Carrillo

Materials 2020, 13(11), 2534; https://doi.org/10.3390/ma13112534 - 03 Jun 2020

Cited by 6 | Viewed by 3240

Abstract

Fiber-reinforced foamed concrete (FRFC) is a lightweight material that has the potential to perform well in seismic applications due to its low density and improved mechanical properties. However, studies focused on the seismic assessment of this material are limited. In this work, U-shaped [...] Read more.

Fiber-reinforced foamed concrete (FRFC) is a lightweight material that has the potential to perform well in seismic applications due to its low density and improved mechanical properties. However, studies focused on the seismic assessment of this material are limited. In this work, U-shaped wall specimens, made of FRFC reinforced with henequen fibers and plain foamed concrete (PFC) with a density of 900 kg/m³, were subjected to shaking table tests. PFC and FRFC were characterized using compression and tension tests. FRFC exhibited enhanced mechanical properties, which were attributed to the fibers. The dynamic tests showed that U-shaped walls made of FRFC performed better than those made of PFC. The time period prior to the collapse of the FRFC U-shaped walls was longer than that of the PFC specimens, which was attributed to the enhanced specimen integrity by the fibers. Finite element simulations of the shaking table test allowed for the prediction of the stress concentration and plastic strain that may lead to the failure of the U-shaped wall. These results showed that U-shaped walls made of FRFC have the potential to perform well in seismic applications, however, these results are preliminary and further studies are needed to support the findings of this work. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 4682 KiB

Open AccessArticle

Distribution Map of Frost Resistance for Cement-Based Materials Based on Pore Structure Change

by Nguyen Xuan Quy, Takumi Noguchi, Seunghyun Na, Jihoon Kim and Yukio Hama

Materials 2020, 13(11), 2509; https://doi.org/10.3390/ma13112509 - 31 May 2020

Cited by 5 | Viewed by 2227

Abstract

This paper presents a prediction method and mathematical model based on experimental results for the change in pore structure of cement-based materials due to environmental conditions. It focuses on frost damage risk to cement-based materials such as mortar. Mortar specimens are prepared using [...] Read more.

This paper presents a prediction method and mathematical model based on experimental results for the change in pore structure of cement-based materials due to environmental conditions. It focuses on frost damage risk to cement-based materials such as mortar. Mortar specimens are prepared using water, ordinary Portland cement, and sand and the pore structure is evaluated using mercury intrusion porosimetry. New formulas are proposed to describe the relationship between the pore structure change and the modified maturity and to predict the durability factor. A quantitative prediction model is established from a modified maturity function considering the influences of environmental factors like temperature and relative humidity. With this model, the frost resistance of cement-based materials can be predicted based on weather data. Using the prediction model and climate data, a new distribution map of frost damage risk is created. It is found that summer weather significantly affects frost resistance, owing to the change in pore structure of cement-based mortar. The model provides a valuable tool for predicting frost damage risk based on weather data and is significant for further research. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 9838 KiB

Open AccessArticle

Fracture Properties Evaluation of Cellulose Nanocrystals Cement Paste

by SeyedAli Ghahari, Lateef N. Assi, Ali Alsalman and Kürşat E. Alyamaç

Materials 2020, 13(11), 2507; https://doi.org/10.3390/ma13112507 - 31 May 2020

Cited by 62 | Viewed by 5427

Abstract

Due to the need for high-performance and sustainable building materials, the investigation of the determination of fracture toughness of cement paste using new and sustainable materials, such as cellulose nanocrystals (CNCs) is worthwhile. Contrary to other well-known nano-reinforcement particles, such as carbon nanotubes, [...] Read more.

Due to the need for high-performance and sustainable building materials, the investigation of the determination of fracture toughness of cement paste using new and sustainable materials, such as cellulose nanocrystals (CNCs) is worthwhile. Contrary to other well-known nano-reinforcement particles, such as carbon nanotubes, CNCs are less toxic; therefore, they have less safety and environmental risks. Fracture behavior of cement paste has been studied intensively for a long time. However, the incorporation of new materials in the cement paste, such as cellulose nanocrystal materials (CNCs), has not been fully investigated. In this paper, the fracture behavior, compressive strength, and hydration properties of cement paste reinforced with cellulose nanocrystal particles were studied. At the age of 3, 7, and 28 days, a three-point bending moment test, and a calorimetry and thermogravimetric analysis, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX) analysis were performed on the water-to-binder-weight ratio of 0.35 cement paste, containing 0.0%, 0.2%, and 1.0% volume cellulose nanocrystals. Results indicated that the fracture properties and compressive strength were improved for the sample containing 0.2% CNCs. Preliminary results indicate that CNCs can improve the fracture behavior of cementitious materials and can be considered as a renewable and sustainable material in construction. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 1791 KiB

Open AccessArticle

Corrosion Behavior of AISI 304 Stainless Steel Reinforcements in SCBA-SF Ternary Ecological Concrete Exposed to MgSO₄

by Hilda A. Ariza-Figueroa, Juan Bosch, Miguel Angel Baltazar-Zamora, René Croche, Griselda Santiago-Hurtado, Laura Landa-Ruiz, José M. Mendoza-Rangel, José M. Bastidas, Facundo Almeraya-Calderón and David M. Bastidas

Materials 2020, 13(10), 2412; https://doi.org/10.3390/ma13102412 - 24 May 2020

Cited by 21 | Viewed by 3248

Abstract

In this study, ternary ecological concrete (TEC) mixtures were produced with partial substitution of the ordinary Portland cement (OPC) by 10%, 20%, and 30% of sugar cane bagasse ash (SCBA) and silica fume (SF); a control mixture (100% OPC) was prepared according to [...] Read more.

In this study, ternary ecological concrete (TEC) mixtures were produced with partial substitution of the ordinary Portland cement (OPC) by 10%, 20%, and 30% of sugar cane bagasse ash (SCBA) and silica fume (SF); a control mixture (100% OPC) was prepared according to ACI 211.1 standard. The studied TEC specimens were reinforced with AISI 304 stainless steel and AISI 1018 carbon steel rebars. TEC reinforced specimens were immersed in two different electrolytes, a control (DI-water) and 3.5 wt.% MgSO₄ solution, for 180 days. The electrochemical corrosion was monitored by corrosion potential (E_corr) according to ASTM C-876-15 standard, and the linear polarization resistance (LPR) technique using ASTM G59 standard. The E_corr and current density i_corr results show that AISI 304 stainless steel rebars have a high corrosion resistance, with i_corr values below 0.1 µA/cm², which is interpreted as a level of negligible corrosion. The best corrosion performance was found for the TEC mixture made with a 20% addition of blend of sugar cane bagasse ash-silica fume (SCBA-SF) to the OPC. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 6064 KiB

Open AccessArticle

Influence of Phosphorus Slag on Physical and Mechanical Properties of Cement Mortars

by Min Pang, Zhenping Sun, Ming Chen, Jianlei Lang, Jiayan Dong, Xu Tian and Jiliang Sun

Materials 2020, 13(10), 2390; https://doi.org/10.3390/ma13102390 - 22 May 2020

Cited by 21 | Viewed by 2584

Abstract

Influences of phosphorus slag from 10% to 50% (by mass) on the setting time and the water requirement of the normal consistency of cement pastes, flowability, resistance to carbonation, and the compressive strength of cement mortars were investigated. The physical activation by improving [...] Read more.

Influences of phosphorus slag from 10% to 50% (by mass) on the setting time and the water requirement of the normal consistency of cement pastes, flowability, resistance to carbonation, and the compressive strength of cement mortars were investigated. The physical activation by improving fineness and the chemical activation by adding the chemical activator were evaluated by the compressive strength of cement mortars with 30% by mass of phosphorus slag. Hydration heat, X-ray diffraction, and scanning electron microscopy were used to study the microstructure of cement pastes and mortars with 30% by mass of phosphorus slag and the chemical activator. Results showed that the setting time of cement pastes was delayed by phosphorus slag from 10% to 50%. Phosphorus slag had nearly no effects on the water requirement of the normal consistency of cement pastes and the flowability of cement mortars. The resistance to carbonation of cement mortars was decreased by phosphorus slag from 10% to 50% according to the acceleration carbonation. The compressive strength of cement mortars was also decreased by phosphorus slag from 10% to 50% and the low activity of phosphorus slag was concluded based on compressive strength of cement mortars. The effect of the chemical activator on the compressive strength of cement mortars with 30% by mass of phosphorus slag was better than improving fineness of phosphorus slag from 300 m²/kg to 450 m²/kg. Both hydration heat and cement hydrates were inhibited by phosphorus slag and could be partly compensated by the chemical activator. Loose morphology and propagations of microcracks were found in cement pastes and mortars with 30% by mass of phosphorus slag. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 12289 KiB

Open AccessArticle

Influences and Mechanisms of Nano-C-S-H Gel Addition on Fresh Properties of the Cement-Based Materials with Sucrose as Retarder

by Deyu Kong, Guangpeng He, Haiwen Pan, Yuehui Weng, Ning Du and Jiansong Sheng

Materials 2020, 13(10), 2345; https://doi.org/10.3390/ma13102345 - 20 May 2020

Cited by 14 | Viewed by 2753

Abstract

Influences and mechanisms of chemically synthesized nano-C-S-H gel addition on fresh properties of the cement-based materials with sucrose as a retarder were investigated in this study. The results showed that the flow value of the fresh cement paste was gradually but slightly reduced [...] Read more.

Influences and mechanisms of chemically synthesized nano-C-S-H gel addition on fresh properties of the cement-based materials with sucrose as a retarder were investigated in this study. The results showed that the flow value of the fresh cement paste was gradually but slightly reduced with increasing nano-C-S-H gel addition due to its fibrous but well-dispersed characteristic in both water and cement paste. The semi-adiabatic calorimetry testing results verified that incorporation of nano-C-S-H gel could greatly mitigate the retarding effect of sucrose on cement hydration. The total organic carbon (TOC) indicated that the addition of the nano-C-S-H gel helps to reduce adsorption of the sucrose molecules into the protective layer, thus the semi-permeability of the protective layer was less reduced and that is why the addition of the nano-C-S-H gel can mitigate the retardation caused by the sucrose. Through XRD analysis, it was found that the CH crystals are more prone to grow along the (0001) plane with larger size in the paste with nano-C-S-H addition before the induction period starts, because the C-S-H nanoparticles can form 3D network to slow down the diffusion rate of the released ions and eliminate the convection in the paste, thus suppress the 3D nucleation and growth of the CH crystals. The XRD analysis also indicated a refinement of the ettringite crystals in the paste with sucrose addition, but introduction of nano-C-S-H gel did not show further refinement, which was also verified by the SEM observation. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 4685 KiB

Open AccessArticle

Experimental Laboratory Testing on Behavior of Dowels in Concrete Pavements

by Andrea Zuzulova, Jiri Grosek and Michal Janku

Materials 2020, 13(10), 2343; https://doi.org/10.3390/ma13102343 - 20 May 2020

Cited by 7 | Viewed by 2313

Abstract

This paper describes the testing of effectiveness and behavior of dowels placed in transversal joints of concrete pavements, while focusing on dimensions and quality of commonly used materials. The analysis uses experimental tests in laboratory conditions which were performed independently in the Czech [...] Read more.

This paper describes the testing of effectiveness and behavior of dowels placed in transversal joints of concrete pavements, while focusing on dimensions and quality of commonly used materials. The analysis uses experimental tests in laboratory conditions which were performed independently in the Czech Republic and Slovak Republic. The comparison of quality as well as potential use of alternative materials of dowels is made with the use of developed tests focusing on main requirements, such as longitudinal displacement in cement concrete, resistance of coating to damage, and reduced potential to concrete damage. Furthermore, the paper describes and compares loading results of the relative concrete deformations around dowels by strain gauges that were analyzed. Results of deformations on beams with an inserted dowel and the findings that were observed during the measurement are presented. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 9630 KiB

Open AccessArticle

Study on Mechanical Properties of Hybrid Polypropylene-Steel Fiber RPC and Computational Method of Fiber Content

by Chunling Zhong, Mo Liu, Yunlong Zhang, Jing Wang, Dong Liang and Luyao Chang

Materials 2020, 13(10), 2243; https://doi.org/10.3390/ma13102243 - 13 May 2020

Cited by 11 | Viewed by 2156

Abstract

On the basis of determining the optimum content of polypropylene fiber reactive powder concrete (RPC), the influence of different steel fiber content on the compressive strength and splitting tensile strength of hybrid polypropylene-steel fiber RPC was studied. The particle morphology and pore parameters [...] Read more.

On the basis of determining the optimum content of polypropylene fiber reactive powder concrete (RPC), the influence of different steel fiber content on the compressive strength and splitting tensile strength of hybrid polypropylene-steel fiber RPC was studied. The particle morphology and pore parameters of hybrid polypropylene-steel fiber RPC were analyzed by combining scanning electron microscope (SEM) with image-pro plus (IPP) software. The results showed that the RPC ductility can be further improved on the basis of polypropylene fiber RPC, the compressive strength and splitting tensile strength of polypropylene fiber. The optimum content of hybrid polypropylene-steel fiber RPC is 0.15% polypropylene fiber, 1.75% steel fiber. Hybrid polypropylene-steel fiber RPC is mainly composed of particles with small particle size. The particle area ratio first increased and decreased with the increase of steel fiber content, and the maximum steel fiber content is 1.75%. The pore area ratio first decreased and increased with the increase of steel fiber content, and the pore area ratio is the smallest when the steel fiber content is 1.75%. The calculation methods of polypropylene fiber content and steel fiber content and 28-day RPC compressive strength and splitting tensile strength are proposed to select polypropylene fiber content and steel fiber content flexibly according to different engineering requirements, which can provide important guidance for the popularization and application of RPC in practical engineering. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 5686 KiB

Open AccessArticle

Influence of Restrained Condition on Mechanical Properties, Frost Resistance, and Carbonation Resistance of Expansive Concrete

by Nguyen Duc Van, Emika Kuroiwa, Jihoon Kim, Hyeonggil Choi and Yukio Hama

Materials 2020, 13(9), 2136; https://doi.org/10.3390/ma13092136 - 05 May 2020

Cited by 11 | Viewed by 2557

Abstract

This paper presents the results of an experimental investigation of the effect of the restrained condition on the mechanical properties, frost resistance, and carbonation resistance of expansive concrete with different water–binder ratios. In this study, length change ratio test, expansion strain test, compressive [...] Read more.

This paper presents the results of an experimental investigation of the effect of the restrained condition on the mechanical properties, frost resistance, and carbonation resistance of expansive concrete with different water–binder ratios. In this study, length change ratio test, expansion strain test, compressive strength test, mercury intrusion porosimetry test, underwater weighing test, freezing–thawing test, and accelerated carbonation test were performed to evaluate the mechanical properties, pore size distribution, total porosity, and durability of expansive concrete under both restrained and unrestrained conditions. The test results indicate that the length change ratio and expansion strain of the expansive concrete were controlled by the restrained condition. The compressive strength of expansive concrete was enhanced by the triaxial restraining when the amount of expansive additive was 40 kg/m³ of concrete. Two hypotheses were described to explain the change of pore structure change expansive mortar. The results also indicate that the carbonation resistance and frost resistance were improved by the uniaxial restrained condition. Furthermore, the effect of the restrained condition must be considered to evaluate not only the experimental results of the expansive concrete with a high EX replacement level but also the expansive concrete combining other cement replacement materials. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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12 pages, 2563 KiB

Open AccessArticle

Study on the Influence of Calcined Underground Ant Nest Powder on the Durability of Concrete

by Wei Zhou, Peng Zhu, Wenjun Qu, Wu Yao and Shengji Wu

Materials 2020, 13(9), 2119; https://doi.org/10.3390/ma13092119 - 02 May 2020

Cited by 2 | Viewed by 2038

Abstract

Ants have strict requirements on the building materials of the nest, such as the size, weight, luster and color of soil particles. The soil of underground ant nests is composed of clay particles cemented together to form a hard brick-like material. The ant [...] Read more.

Ants have strict requirements on the building materials of the nest, such as the size, weight, luster and color of soil particles. The soil of underground ant nests is composed of clay particles cemented together to form a hard brick-like material. The ant nest powder shows pozzolanic activity after calcination, which can meet the requirements for active admixture of concrete. Under the standard curing condition, the influence of calcined ant nest clay powder (CANCP) on the durability of concrete is evaluated by chloride penetration resistance, carbonization resistance and freeze–thaw resistance, and the influence of the powder content is investigated. The results show that when the content of CANCP is less than 10%, the chloride penetration resistance of concrete increases with content of CANCP. In the early stage of carbonation, the greater the content of CANCP, the higher the carbonization rate of concrete. In the middle and later stage of carbonation, the carbonation rate of CANCP concrete is significantly lower than that in the early stage, and the carbonation depth is linearly related to the carbonation time. When the content of CANCP is less than 20%, the freeze–thaw resistance of CANCP concrete is better than that of the reference concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 3109 KiB

Open AccessArticle

Effect of Graphene Oxide Nanosheets on Physical Properties of Ultra-High-Performance Concrete with High Volume Supplementary Cementitious Materials

by Yu-You Wu, Jing Zhang, Changjiang Liu, Zhoulian Zheng and Paul Lambert

Materials 2020, 13(8), 1929; https://doi.org/10.3390/ma13081929 - 19 Apr 2020

Cited by 30 | Viewed by 3042

Abstract

Nanomaterials have been increasingly employed for improving the mechanical properties and durability of ultra-high-performance concrete (UHPC) with high volume supplementary cementitious materials (SCMs). Recently, graphene oxide (GO) nanosheets have appeared as one of the most promising nanomaterials for enhancing the properties of cementitious [...] Read more.

Nanomaterials have been increasingly employed for improving the mechanical properties and durability of ultra-high-performance concrete (UHPC) with high volume supplementary cementitious materials (SCMs). Recently, graphene oxide (GO) nanosheets have appeared as one of the most promising nanomaterials for enhancing the properties of cementitious composites. To date, a majority of studies have concentrated on cement pastes and mortars with fewer investigations on normal concrete, ultra-high strength concrete, and ultra-high-performance cement-based composites with a high volume of cement content. The studies of UHPC with high volume SCMs have not yet been widely investigated. This paper presents an experimental investigation into the mini slump flow and physical properties of such a UHPC containing GO nanosheets at additions from 0.00 to 0.05% by weight of cement and a water–cement ratio of 0.16. The study demonstrates that the mini slump flow gradually decreases with increasing GO nanosheet content. The results also confirm that the optimal content of GO nanosheets under standard curing and under steam curing is 0.02% and 0.04%, respectively, and the corresponding compressive and flexural strengths are significantly improved, establishing a fundamental step toward developing a cost-effective and environmentally friendly UHPC for more sustainable infrastructure. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 1674 KiB

Open AccessArticle

Optimal Design of Seismic Resistant RC Columns

by Paolo Foraboschi

Materials 2020, 13(8), 1919; https://doi.org/10.3390/ma13081919 - 19 Apr 2020

Cited by 22 | Viewed by 2889

Abstract

Although the author is well aware that it is nothing special, presented here is the method that he uses to design the columns of a seismic resistant reinforced concrete structure, in hopes that this could be of use to someone. The method, which [...] Read more.

Although the author is well aware that it is nothing special, presented here is the method that he uses to design the columns of a seismic resistant reinforced concrete structure, in hopes that this could be of use to someone. The method, which is directed at satisfying the capacity design requirements without excessively large sections, consists of proportioning the column so that the seismic action effects shall be resisted by the maximum of the bending moment–axial force interaction curve. That design condition is defined by two equations whose solution provides the optimal aspect ratio (or, alternatively, the optimal section side length) and the maximum feasible reinforcement ratio. The method can be used directly to determine the optimal column for given beam spans and vertical loads, or indirectly to determine the optimal beam spans and vertical loads for given cross-sectional dimensions. The paper presents the method, including its proof, and some applications together with the analysis on the optimality of the obtained solutions. The method is intended especially for the practicing structural engineer, though it may also be useful for educators, students, and building officials. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 6244 KiB

Open AccessArticle

Tomography-Based Investigation on the Carbonation Behavior through the Surface-Opening Cracks of Sliced Paste Specimen

by Dong Cui, Xiaobao Zuo, Keren Zheng and Sudip Talukdar

Materials 2020, 13(8), 1804; https://doi.org/10.3390/ma13081804 - 11 Apr 2020

Cited by 4 | Viewed by 1787

Abstract

Understanding the cracking behavior during carbonation is of high importance, and the cracks can serve as a shortcut for CO₂ diffusion, which can further accelerate the carbonation process itself. In this study, a sliced paste sample was taken for an accelerated carbonation [...] Read more.

Understanding the cracking behavior during carbonation is of high importance, and the cracks can serve as a shortcut for CO₂ diffusion, which can further accelerate the carbonation process itself. In this study, a sliced paste sample was taken for an accelerated carbonation test, and the cracking behavior, as well as its impact on carbonation, was investigated through a novel extended attenuation method based on X-ray (XRAM) which is performed primarily on computed tomography (CT). Surface-opening cracks at different carbonation ages were rendered, based on which a full view on the carbonation-cracking behavior was built. The results reveal that the crack paths can rapidly be occupied by CO₂, and that leads to the generation of V-shaped carbonation cusps pervading the carbonation fronts. The V-shaped carbonation cusps were mostly generated at the early carbonation age (within 14 days), attesting to a less intact sample surface as compared to the inside area. Moreover, this study confirms that the carbonated area would split into two independent zones with variant carbonation degree due to the increased humidity level near the sample surface. The current work reveals the interconnection between carbonation and cracking, and the results can be used for the designing of cement-based materials with better carbonation and cracking resistance. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 8134 KiB

Open AccessArticle

Mechanical Characteristics of Cement-Based Grouting Material in High-Geothermal Tunnel

by Mingnian Wang, Yunpeng Hu, Cheng Jiang, Yicheng Wang, Dagang Liu and Jianjun Tong

Materials 2020, 13(7), 1572; https://doi.org/10.3390/ma13071572 - 29 Mar 2020

Cited by 17 | Viewed by 3114

Abstract

The cement-based grouting materials used for practical purposes in high-geothermal tunnels are inevitably affected by humidity and high temperature, leading to the deterioration of mechanical properties. Based on the characteristics of changing high temperatures and two typical conditions of hot-humid and hot-dry environments [...] Read more.

The cement-based grouting materials used for practical purposes in high-geothermal tunnels are inevitably affected by humidity and high temperature, leading to the deterioration of mechanical properties. Based on the characteristics of changing high temperatures and two typical conditions of hot-humid and hot-dry environments in high-geothermal tunnels, many mechanical strength tests were carried out on the grouting material cured under different environmental conditions. The study results indicated that high temperature and low relative humidity were unfavorable to the development of mechanical characteristics of grouting material, but the coupling effect of two factors could improve the strength at early ages and reduce the degradation of long-term strength. As the curing temperature exceeded 56.3 °C, the humidity effect on strength played a more important role in recovering the strength of grouting material damaged by high temperature. Temperature had more significant impact on the relative peak stress while the relative humidity had greater influence on the relative peak strain. A calculation compressive constitutive model was prospered, which considering both temperature and relative humidity. The study results may provide much valuable experimental data and theoretical supporting for the design of compression constitutive of cement-based grouting material in high-geothermal tunnel. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 7152 KiB

Open AccessArticle

Deterioration Process of Concrete Exposed to Internal Sulfate Attack

by Weifeng Chen, Bei Huang, Yuexue Yuan and Min Deng

Materials 2020, 13(6), 1336; https://doi.org/10.3390/ma13061336 - 15 Mar 2020

Cited by 31 | Viewed by 3191

Abstract

Damage to concrete structures with gypsum-contaminated aggregate occurs frequently. Aggregates in much of the southern part of China are contaminated with gypsum. Therefore, in this study, the effects of using different quantities of gypsum-contaminated aggregate on the expansion and compressive strength of concrete [...] Read more.

Damage to concrete structures with gypsum-contaminated aggregate occurs frequently. Aggregates in much of the southern part of China are contaminated with gypsum. Therefore, in this study, the effects of using different quantities of gypsum-contaminated aggregate on the expansion and compressive strength of concrete were investigated over a period of one year. Two groups of concrete were designed with the gypsum-contaminated aggregate containing different parts of fine and coarse aggregate, respectively. The SO₃ contents were 0%, 0.5%, 1%, 1.5%, 3%, 5%, and 7% by weight of aggregate. X-ray diffraction (XRD), thermogravimetry (TG), and differential scanning calorimetry (DSC) were used to analyze the change in mineral composition over time. The microstructure was also studied by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that significant expansion and great loss in compressive strength did not occur in concrete if the content of SO₃ lay below 1.5% and 3% in fine and coarse aggregates, respectively. The concentration of sulfate ions in concrete was not enough to form new a phase of gypsum. During the process of internal sulfate attack, the content of gypsum decreased and the content of ettringite increased. Ettringite was the main reason for the expansion damage of concrete. Additionally, the fracture mode of internal sulfate attack on concrete was the crack extension from gypsum to paste; finally, the aggregate separated from the paste. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 6230 KiB

Open AccessArticle

Experimental Investigation on the Freeze–Thaw Resistance of Steel Fibers Reinforced Rubber Concrete

by Tao Luo, Chi Zhang, Chaowei Sun, Xinchao Zheng, Yanjun Ji and Xiaosa Yuan

Materials 2020, 13(5), 1260; https://doi.org/10.3390/ma13051260 - 10 Mar 2020

Cited by 26 | Viewed by 3127

Abstract

The reuse of rubber in concrete results in two major opposing effects: an enhancement in durability and a reduction in mechanical strength. In order to strengthen the mechanical properties of rubber concrete, steel fibers were added in this research. The compressive strength, the [...] Read more.

The reuse of rubber in concrete results in two major opposing effects: an enhancement in durability and a reduction in mechanical strength. In order to strengthen the mechanical properties of rubber concrete, steel fibers were added in this research. The compressive strength, the four-point bending strength, the mass loss rate, and the relative dynamic elastic modulus of steel fiber reinforced rubber concrete, subjected to cyclic freezing and thawing, were tested. The effects of the content of steel fibers on the freeze–thaw resistance are discussed. The microstructure damage was captured and analyzed by Industrial Computed Tomography (ICT) scanning. Results show that the addition of 2.0% steel fibers can increase the compressive strength of rubber concrete by 26.6% if there is no freeze–thaw effect, but the strengthening effect disappears when subjected to cyclic freeze–thaw. The enhancement of steel fibers on the four-point bending strength is effective under cyclic freeze–thaw. The effect of steel fibers is positive on the mass loss rate but negative on the relative dynamic elastic modulus. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 9825 KiB

Open AccessArticle

Bond-Slip Behavior between Stainless Steel Rebars and Concrete

by Margherita Pauletta, Nicola Rovere, Norbert Randl and Gaetano Russo

Materials 2020, 13(4), 979; https://doi.org/10.3390/ma13040979 - 21 Feb 2020

Cited by 32 | Viewed by 4138

Abstract

Maintenance of reinforced concrete structures is a prevailing topic, especially with regard to lifeline structures and bridges, many of which are now designed with a service life beyond 100 years. Reinforcement made of ordinary (carbon) steel may corrode in aggressive environments. Stainless steel, [...] Read more.

Maintenance of reinforced concrete structures is a prevailing topic, especially with regard to lifeline structures and bridges, many of which are now designed with a service life beyond 100 years. Reinforcement made of ordinary (carbon) steel may corrode in aggressive environments. Stainless steel, being much more resistant to corrosion, is a valid solution to facilitate the protection of the works, increasing the service life and reducing the need for repair and maintenance. Despite the potential for stainless steel to reduce maintenance costs, studies investigating the influence of stainless steel on the behavior of reinforced concrete structures are limited. This study investigated the bond behavior of stainless steel rebars by means of experimental tests on reinforced concrete specimens with different concrete cover thicknesses, concrete strengths, and bar diameters. In each case, identical specimens with carbon steel reinforcement were tested for comparison. The failure modes of the specimens were examined, and a bond stress–slip relationship for stainless steel bars was established. This research shows that the bond behavior of stainless steel rebars is comparable to that of carbon steel bars. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 12134 KiB

Open AccessArticle

Load Capacity and Displacement of Recycled Concrete and Self-Insulation Block Masonry Wall

by Huizhi Zhang, Jifeng Liu, Yang Yue, Xiuqin Cui and Yuezong Lian

Materials 2020, 13(4), 863; https://doi.org/10.3390/ma13040863 - 14 Feb 2020

Cited by 3 | Viewed by 2260

Abstract

In order to discuss the load capacity and displacement of masonry constructed with recycled concrete and self-insulation blocks, one type of 10.6 MPa compressive strength block and three kinds of mortar with M15, M10, and M5 compressive strengths are selected. The constitutive model [...] Read more.

In order to discuss the load capacity and displacement of masonry constructed with recycled concrete and self-insulation blocks, one type of 10.6 MPa compressive strength block and three kinds of mortar with M15, M10, and M5 compressive strengths are selected. The constitutive model and corresponding parameters selection of different materials in the ABAQUS numerical simulation are analyzed, and the numerical simulation analysis and experimental tests of the load capacity and displacement of masonry constructed with mortars of different strengths are carried out. The results show that masonry compression failure is controlled by the mortar or block that has the lower compressive strength. The displacement of masonry increases with the mortar compressive strength increase, and the higher mortar compressive strength is beneficial for improving the load capacity and displacement of masonry. Reasonable selection of the constitutive model and parameters will help to obtain reasonable results for the ABAQUS numerical simulation. Construction quality and loading method will affect the load capacity and displacement of the masonry. The above conclusion can provide reference for the engineering application of recycled concrete and self-insulation blocks. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 6057 KiB

Open AccessArticle

Mechanical Properties of Concrete Containing Liquefied Red Mud Subjected to Uniaxial Compression Loads

by Gyeongcheol Choe, Sukpyo Kang and Hyeju Kang

Materials 2020, 13(4), 854; https://doi.org/10.3390/ma13040854 - 13 Feb 2020

Cited by 14 | Viewed by 2733

Abstract

This study used liquefied red mud (RM) sludge, an aluminum industry by-product, as a construction material. Accordingly, various methods were examined that used the fabricated liquefied red mud (LRM) as an admixture for concrete, and the mechanical properties of concrete were then evaluated [...] Read more.

This study used liquefied red mud (RM) sludge, an aluminum industry by-product, as a construction material. Accordingly, various methods were examined that used the fabricated liquefied red mud (LRM) as an admixture for concrete, and the mechanical properties of concrete were then evaluated according to the cement type and the amount of LRM. The LRM mixing methods (replacement and addition) were compared, and the slump and compressive strengths of concrete were evaluated for each method. To examine the mechanical properties according to the cement type and the amount of LRM, two types of cement (ordinary Portland cement and slag cement (SC)) were used, and 20 and 40 wt% LRM (with respect to the cement weight) were added. The mechanical properties of the stress–strain curve (SSC), compressive strength, peak strain, and elastic modulus were quantified. When the slump and compressive strength of concrete were considered based on the experimental results, the addition LRM mixing method was recommended as the appropriate method for LRM. As the addition of LRM increased, the mechanical properties of concrete degraded. However, when SC was used, the mechanical properties did not significantly change when different amounts of LRM were added (up to 20%). In addition, the SSC of LRM concrete could be approximated based on the use of the relationship of the compressive strength and peak strain according to the cement type and the amount of LRM. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 6026 KiB

Open AccessArticle

Durability and Aesthetics of Architectural Concrete under Chloride Attack or Carbonation

by Honglei Chang, Penggang Wang, Zuquan Jin, Gang Li, Pan Feng, Shoujie Ye and Jian Liu

Materials 2020, 13(4), 839; https://doi.org/10.3390/ma13040839 - 12 Feb 2020

Cited by 9 | Viewed by 2436

Abstract

Architectural concrete has been wildly used nowadays, and those served in an offshore environment often suffer from chloride penetration and carbonation. To assess the protection and decoration performances of architectural concrete, this study exposed architectural concrete to actual marine environments and accelerated carbonation [...] Read more.

Architectural concrete has been wildly used nowadays, and those served in an offshore environment often suffer from chloride penetration and carbonation. To assess the protection and decoration performances of architectural concrete, this study exposed architectural concrete to actual marine environments and accelerated carbonation conditions. The chloride and carbonation resistance of architectural concrete was determined to evaluate the protection performance, and the corresponding surface-color-consistency was adopted to characterize its decoration performance. The results show that the total and free chloride of concrete in the marine atmosphere zone and the tidal zone generally decreases with depth; chloride content arguments significantly with exposure time, with a chloride maximum peak near the surface. Moreover, the chloride diffusion coefficient is small throughout the measurements, indicating the superior chloride resistance of architectural concrete. Furthermore, architectural concrete also possesses excellent carbonation resistance based on the carbonation depth data obtained from the carbonation experiment. Therefore, architecture concrete served as protection covers can withstand both the chloride attack and carbonation tested in this paper. In addition, carbonation was found to have a profound influence on the aesthetics of architectural concrete. Therefore, carbonation should be carefully handled for better maintaining the aesthetic appearance of architectural concrete in long-term service. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 4168 KiB

Open AccessArticle

A Prediction Model of the Concrete Cracking Induced by the Non-Uniform Corrosion of the Steel Reinforcement

by Wenjun ZHU, Kequan YU, Yude XU, Kai ZHANG and Xiaopei CAI

Materials 2020, 13(4), 830; https://doi.org/10.3390/ma13040830 - 12 Feb 2020

Cited by 9 | Viewed by 3061

Abstract

This paper investigates the influence of non-uniform corrosion in the transversal direction of the steel reinforcement on the cracking propagation of the concrete cover. An analytical model is proposed for the prediction of the corrosion-induced cracking performance. Both the thick cylinder theory of [...] Read more.

This paper investigates the influence of non-uniform corrosion in the transversal direction of the steel reinforcement on the cracking propagation of the concrete cover. An analytical model is proposed for the prediction of the corrosion-induced cracking performance. Both the thick cylinder theory of the concrete and the effect of transversal non-uniform corrosion of the steel reinforcement are involved by considering the corrosion layer of the corrosion products and a layer of concrete with the corrosion products filled with the pores. A three-stage corrosion-induced cracking of the concrete is proposed: corrosion without expansive stress to the concrete, corrosion with expansive stress to the adjacent concrete, as well as the corrosion-induced cracking of the concrete. By considering the non-uniform corrosion of the steel reinforcement and the tensile stress induced by the volumetric expansion of the corrosion products, the cracking initiation resulting from the non-uniform corrosion was involved in the prediction model. The models were also validated by the experimental results from both the corroded specimens and the existing literature, which would be helpful for the evaluation of the existing reinforced concrete constructions in the marine environment. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 4914 KiB

Open AccessArticle

Degradation of Axial Ultimate Load-Bearing Capacity of Circular Thin-Walled Concrete-Filled Steel Tubular Stub Columns after Corrosion

by Fengjie Zhang, Junwu Xia, Guo Li, Zhen Guo, Hongfei Chang and Kejin Wang

Materials 2020, 13(3), 795; https://doi.org/10.3390/ma13030795 - 10 Feb 2020

Cited by 28 | Viewed by 3429

Abstract

This work aimed to investigate the effects of steel tube corrosion on the axial ultimate load-bearing capacity (AULC) of circular thin-walled concrete-filled steel tubular (CFST) members. Circular thin-walled CFST stub column specimens were made of steel tubes with various wall-thicknesses. These CFST column [...] Read more.

This work aimed to investigate the effects of steel tube corrosion on the axial ultimate load-bearing capacity (AULC) of circular thin-walled concrete-filled steel tubular (CFST) members. Circular thin-walled CFST stub column specimens were made of steel tubes with various wall-thicknesses. These CFST column specimens were subjected to an accelerated corrosion test, where the steel tubes were corroded to different degrees of corrosion. Then, these CFST specimens with corroded steel tubes experienced an axial static loading test. Results show that the failure patterns of circular thin-walled CFST stub columns with corroded steel tubes are different from those of the counterpart CFST columns with ordinary wall-thickness steel tubes, which is a typical failure mode of shear bulging with slight local outward buckling. The ultimate strength and plastic deformation capacity of the CFST specimens decreased with the increasing degree of steel corrosion. The failure modes of the specimens still belonged to ductile failure because of the confinement of outer steel tube. The degree of steel tube corrosion, diameter-to-thickness ratio, and confinement coefficient had substantial influences on the AULC and the ultimate compressive strength of circular thin-walled CFST stub columns. A simple AULC prediction model for corroded circular thin-walled CFST stub columns was presented through the regression of the experimental data and parameter analysis. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 6609 KiB

Open AccessArticle

Experimental Study and Failure Criterion Analysis on Combined Compression-Shear Performance of Self-Compacting Concrete

by Jingrong Wang, Faxiang Xie, Chuanlong Zhang and Jing Ruan

Materials 2020, 13(3), 713; https://doi.org/10.3390/ma13030713 - 05 Feb 2020

Cited by 14 | Viewed by 2446

Abstract

To investigate the combined compression-shear performance of self-compacting concrete (SCC), eight groups of concrete specimens under different axial compression ratios were designed, and the composite performance under different axial stresses was carried out by hydraulic servo machine. The uniaxial and tensile splitting strength [...] Read more.

To investigate the combined compression-shear performance of self-compacting concrete (SCC), eight groups of concrete specimens under different axial compression ratios were designed, and the composite performance under different axial stresses was carried out by hydraulic servo machine. The uniaxial and tensile splitting strength of SCC were also included in the study. The failure modes of SCC were presented, discussed, and compared with normal concrete (NC). The characteristic points of stress-strain curves of SCC specimens from the experiments were extracted and analyzed under different axial compression stress. Based on the experimental results, the shear strength of compression-shear load was divided into cohesive stress and residual friction stress. The variation of residual stress and cohesive stress under the combined compression-shear stress was analyzed, and the relationship was obtained by numerical regression. Research results indicated that the residual stress increases linearly with the compression stress while the cohesive stress increased at first and then decreased. The research found that the friction coefficient of SCC was much smaller than NC due to the lack of interlocking effect. Utilizing the compression-shear strength of SCC, the material failure criteria of SCC were proposed from the view of shear failure strength and octahedral stress space, which could fit the experimental results confidently following the mathematical regression analysis. The comparison with data from other literature shows favorable consistence with the obtained criteria. The results of the study could be beneficial complement in engineering practices where SCC was applicable. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 3305 KiB

Open AccessArticle

Additional Porosity as a Side Effect of Polycarboxylate Addition and Its Influence on Concrete’s Scaling Resistance

by Aneta Nowak-Michta

Materials 2020, 13(2), 316; https://doi.org/10.3390/ma13020316 - 09 Jan 2020

Cited by 6 | Viewed by 1908

Abstract

A side effect of using modified polycarboxylates to liquefy a concrete mix is additional pores in the concrete. They change the air void system in hardened concretes, and can be used to evaluate the freeze–thaw resistance of concretes. The purpose of this study [...] Read more.

A side effect of using modified polycarboxylates to liquefy a concrete mix is additional pores in the concrete. They change the air void system in hardened concretes, and can be used to evaluate the freeze–thaw resistance of concretes. The purpose of this study is to determine the impact of the abovementioned quantitative and qualitative parameters on the freeze–thaw resistance of concretes. The research program was performed on eight sets of air-entraining and non-air-entraining concretes with a variable content of superplasticizer based on modified polycarboxylates. The basic composition of and air-entraining admixture content in the air-entraining concrete mixtures were held constant. Pore structure tests were performed according to EN 480-11. Scaling resistance was determined according to PKN-CEN/TS 12390-9. The results showed that as the content of modified polycarboxylates increased, the pore structure was adversely affected, and, consequently, the air void parameters deteriorated. At the same time, the freeze–thaw resistance of the non-air-entraining concretes decreased. The pores sizes also changed. As the fluidity increased, the specific surface area decreased, and, consequently, the spacing factor increased. The air-entraining concretes, despite the deterioration in the pore structure due to the modified polycarboxylates, were found to be very good quality concretes after 56 freeze–thaw cycles in the presence of 3% NaCl. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 10738 KiB

Open AccessArticle

Expansion of Dolomitic Rocks in TMAH and NaOH Solutions and Its Root Causes

by Huan Yuan, Min Deng, Bi Chen, Weifeng Chen and Zhongyang Mao

Materials 2020, 13(2), 308; https://doi.org/10.3390/ma13020308 - 09 Jan 2020

Cited by 3 | Viewed by 2099

Abstract

In this paper, a tetramethylammonium hydroxide (TMAH) solution and homemade cement without alkali were used to eliminate the influence of the alkali-silica reaction (ASR) on the expansion of dolomitic rocks, and a NaOH solution was used as a comparison agent. The expansion of [...] Read more.

In this paper, a tetramethylammonium hydroxide (TMAH) solution and homemade cement without alkali were used to eliminate the influence of the alkali-silica reaction (ASR) on the expansion of dolomitic rocks, and a NaOH solution was used as a comparison agent. The expansion of concrete microbars and dolomite powder compacts prepared from dolomitic rocks was tested. The expansion cracks and reaction products were investigated by X-ray diffraction, optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that TMAH reacts with dolomite crystals in dolomitic rocks to form brucite and calcite. Through X-ray diffraction and SEM-EDS analysis, it can be determined that the chemical reaction between TMAH and dolomite crystal was dedolomitization. The expansion stress test and concrete microbar expansion test suggest that the alkali carbonate reaction (ACR) can produce expansion. Although both the ASR and the ACR were observed in the NaOH reaction system, but ASRgel was not found in the cracks, indicating that the ASR may be involved in the expansion process of concrete microbars and that the ACR is the root cause of the expansion. However, under the curing conditions of the TMAH solution, many ACR products were found around the crack, indicating that the expansion of the concrete in this system was caused entirely by the ACR. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 24670 KiB

Open AccessFeature PaperArticle

Response of Connections between Concrete Corbels and Safety Barriers

by Sara Cattaneo and Pietro Crespi

Materials 2019, 12(24), 4103; https://doi.org/10.3390/ma12244103 - 08 Dec 2019

Cited by 4 | Viewed by 2495

Abstract

Post-installed anchor systems are widely used in several applications both for retrofit and new constructions due to their flexibility and easiness of installation. For these reasons, their use is very common to connect safety barriers to concrete corbels. However, the design requirements for [...] Read more.

Post-installed anchor systems are widely used in several applications both for retrofit and new constructions due to their flexibility and easiness of installation. For these reasons, their use is very common to connect safety barriers to concrete corbels. However, the design requirements for fastening (Eurocode 2—Part 4, ACI 318 or for post-installed rebar (Eurocode 2-Part 1 can be hardly satisfied due to the geometric restrictions of the application. Additional complications arise for the refurbishment of bridge corbels, which usually requires the removal of the damaged top concrete layer. This paper presents a new anchoring system that consists of the use of additional post-installed U-shaped rebars connecting the lower existing portion of the corbel to the upper (rebuilt) layer, able to carry the required design loads. The proposed solution considers three anchors that transfer the external loads to the corbel, to the existing reinforcements, and to the U-shaped rebars. The system is tested experimentally and validated by using both theoretical (strut and tie modeling) and numerical analyses. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 15001 KiB

Open AccessArticle

Self-Healing Concrete by Biological Substrate

by How-Ji Chen, Ching-Fang Peng, Chao-Wei Tang and Yi-Tien Chen

Materials 2019, 12(24), 4099; https://doi.org/10.3390/ma12244099 - 08 Dec 2019

Cited by 36 | Viewed by 5823

Abstract

At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and [...] Read more.

At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and the repair material. This study aimed to explore the feasibility of using microbial techniques to repair concrete cracks. The bacteria used were environmentally friendly Bacillus pasteurii. In particular, the use of lightweight aggregates as bacterial carriers in concrete can increase the chance of bacterial survival. Once the external environment meets the growth conditions of the bacteria, the vitality of the strain can be restored. Such a system can greatly improve the feasibility and success rate of bacterial mineralization in concrete. The test project included the microscopic testing of concrete crack repair, mainly to understand the crack repair effect of lightweight aggregate concrete with implanted bacterial strains, and an XRD test to confirm that the repair material was produced by the bacteria. The results show that the implanted bacterial strains can undergo Microbiologically Induced Calcium Carbonate Precipitation (MICP) and can effectively fill the cracks caused by external concrete forces by calcium carbonate deposition. According to the results on the crack profile and crack thickness, the calcium carbonate precipitate produced by the action of Bacillus pasteurii is formed by the interface between the aggregate and the cement paste, and it spreads over the entire fracture surface and then accumulates to a certain thickness to form a crack repairing effect. The analysis results of the XRD test also clearly confirm that the white crystal formed in the concrete crack is calcium carbonate. From the above test results, it is indeed feasible to use Bacillus pasteurii in the self-healing of concrete cracks. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 3645 KiB

Open AccessArticle

Does the Carbon Fibre Coating Reinforcement Have an Influence on the Bearing Capacity of High-Performance Self-Compacting Fibre-Reinforced Concrete?

by Krzysztof Ostrowski

Materials 2019, 12(24), 4054; https://doi.org/10.3390/ma12244054 - 05 Dec 2019

Cited by 5 | Viewed by 2787

Abstract

This study investigated the impact of the location of a carbon fibre coated reinforcement ring (CFCRr) inside the structure of high-performance self-compacting fibre-reinforced concrete (HPSCFRC). Nowadays, cement matrix is considered as an alternative binder when reinforcing concrete structures with composite materials. Due to [...] Read more.

This study investigated the impact of the location of a carbon fibre coated reinforcement ring (CFCRr) inside the structure of high-performance self-compacting fibre-reinforced concrete (HPSCFRC). Nowadays, cement matrix is considered as an alternative binder when reinforcing concrete structures with composite materials. Due to the plastic behavior of composite structures at relatively low temperatures when carbon fibres are reinforced with epoxy resin, the author attempted to locate carbon fibres inside a concrete structure. Thanks to this, the reinforcement will be less vulnerable to high temperatures (during a fire) and more compatible with concrete. The fibres act as a perimeter reinforcement that is compatible with the concrete mixture. The position of the CFCRr in the structure of concrete has an influence on the load capacity, stiffness and stress-strain behavior of concrete elements. The research was conducted on circular shape short concrete columns and tested under axial compression. The results demonstrated that by including CFCRr inside a concrete specimen, the maximum compressive strength decreases with an increase in the number of composite rings and a greater distance from the vertical axis of symmetry to the edge of the element. It has been proven in these studies that carbon fibres do not have good adhesive properties between CFCRr and a concrete mixture. As a result of this phenomenon, a shear surface is created, which leads to crack propagation along the CFCRr. Therefore, the presented idea of an internal CFCRr should not be used when designing new concrete structures. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 2225 KiB

Open AccessArticle

Effect of Silica Fume and Fly Ash Admixtures on the Corrosion Behavior of AISI 304 Embedded in Concrete Exposed in 3.5% NaCl Solution

by Miguel Angel Baltazar-Zamora, David M. Bastidas, Griselda Santiago-Hurtado, José Manuel Mendoza-Rangel, Citlalli Gaona-Tiburcio, José M. Bastidas and Facundo Almeraya-Calderón

Materials 2019, 12(23), 4007; https://doi.org/10.3390/ma12234007 - 03 Dec 2019

Cited by 36 | Viewed by 3678

Abstract

The use of supplementary cementitious materials such as fly ash, slag, and silica fume improve reinforced concrete corrosion performance, while decreasing cost and reducing environmental impact compared to ordinary Portland cement. In this study, the corrosion behavior of AISI 1018 carbon steel (CS) [...] Read more.

The use of supplementary cementitious materials such as fly ash, slag, and silica fume improve reinforced concrete corrosion performance, while decreasing cost and reducing environmental impact compared to ordinary Portland cement. In this study, the corrosion behavior of AISI 1018 carbon steel (CS) and AISI 304 stainless steel (SS) reinforcements was studied for 365 days. Three different concrete mixtures were tested: 100% CPC (composite Portland cement), 80% CPC and 20% silica fume (SF), and 80% CPC and 20% fly ash (FA). The concrete mixtures were designed according to the ACI 211.1 standard. The reinforced concrete specimens were immersed in a 3.5 wt.% NaCl test solution to simulate a marine environment. Corrosion monitoring was evaluated using the corrosion potential (E_corr) according to ASTM C876 and the linear polarization resistance (LPR) according to ASTM G59. The results show that AISI 304 SS reinforcements yielded the best corrosion behavior, with E_corr values mainly pertaining to the region of 10% probability of corrosion, and corrosion current density (i_corr) values indicating passivity after 105 days of experimentation and low probability of corrosion for the remainder of the test period. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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11 pages, 8045 KiB

Open AccessArticle

Investigation of the Relationship between Compressive Strength and Hydrate Formation Behavior of Low-Temperature Cured Cement upon Addition of a Nitrite-Based Accelerator

by Jihoon Kim, Daiki Honda, Heesup Choi and Yukio Hama

Materials 2019, 12(23), 3936; https://doi.org/10.3390/ma12233936 - 28 Nov 2019

Cited by 13 | Viewed by 2689

Abstract

When concrete is used for construction in cold-temperature regions, cold-resistant accelerators based on calcium nitrite (Ca(NO₂)₂) and calcium nitrate (Ca(NO₃)₂) are added to prevent early freezing damage. Although cold-resistant accelerators increase the early compressive strength [...] Read more.

When concrete is used for construction in cold-temperature regions, cold-resistant accelerators based on calcium nitrite (Ca(NO₂)₂) and calcium nitrate (Ca(NO₃)₂) are added to prevent early freezing damage. Although cold-resistant accelerators increase the early compressive strength and prevent early freezing damage by promoting cement hydration, the strength enhancement effect owing to the formation of such hydrates has not been evaluated quantitatively thus far. This study covers various types of analysis to understand the relationship between cement hydrate formation behavior and strength development upon the addition of varying amounts of nitrite-based accelerator. We find that the early compressive strength is enhanced by the addition of nitrite-based accelerator via the promotion of the relative production of monosulfate and C-S-H in the early age. However, the development of compressive strength decreases with an increase in the curing age. Furthermore, we find that the promotion of hydration reactions at an early age with the addition of nitrite-based accelerator can affect the formation ratio of each hydrate at a late age. We believe our findings can significantly contribute to developments in concrete application and allied fields. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 2695 KiB

Open AccessArticle

Hydration Kinetics of Portland Cement–Silica Fume Binary System at Low Temperature

by Yao Li, Yonggang Deng and Runqing Liu

Materials 2019, 12(23), 3896; https://doi.org/10.3390/ma12233896 - 26 Nov 2019

Cited by 5 | Viewed by 2474

Abstract

Portland cement–silica fume binary cementitious materials are widely used in engineering construction and have been investigated from micro- to macroscopic aspects. However, the theoretical background on the hydration kinetics of the binary system has not been sufficiently covered in the literature. In this [...] Read more.

Portland cement–silica fume binary cementitious materials are widely used in engineering construction and have been investigated from micro- to macroscopic aspects. However, the theoretical background on the hydration kinetics of the binary system has not been sufficiently covered in the literature. In this study, the hydration dynamic characteristics of the Portland cement–silica fume binary system curing at low temperature were investigated. Hydration kinetics equations were optimized and a hydration model followed by a computer program was developed to calculate the reaction rate constant K and the reaction order n. This model presented that the hydration process of the binary system at low temperature could be divided into three stages, namely, nucleation and growth (NG), interactions at phase boundaries (I), and diffusion (D). The n values for the binary system varied in the range of 1.2 to 1.6, indicating that the hydration of the binary system at low temperature was a complex elementary reaction. Silica fume can reduce the total heat at the later stage of the hydration and the reaction order n, but increase the heat flow at the accelerating stage and the hydration rate constant K. Low temperature prolonged the hydration induction period, decreased and delayed the secondary exothermic peak, as well as reduced the n and K value. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 2232 KiB

Open AccessArticle

Evaluation of the Thermal and Shrinkage Stresses in Restrained High-Performance Concrete

by Yang Yang, Linhao Ma, Jie Huang, Chunping Gu, Zhenjian Xu, Jintao Liu and Tongyuan Ni

Materials 2019, 12(22), 3680; https://doi.org/10.3390/ma12223680 - 08 Nov 2019

Cited by 9 | Viewed by 2401

Abstract

The early age volume deformation is the main course for the cracking of high-performance concrete (HPC). Hence, the shrinkage behavior and the restrained stress development of HPC under different restraints and curing conditions were experimentally studied in this paper. The method to separate [...] Read more.

The early age volume deformation is the main course for the cracking of high-performance concrete (HPC). Hence, the shrinkage behavior and the restrained stress development of HPC under different restraints and curing conditions were experimentally studied in this paper. The method to separate the stress components in the total restraint stress was proposed. The total restrained stress was separated into autogenous shrinkage stress, drying shrinkage stress and thermal stress. The results showed that the developments of the free shrinkage (autogenous shrinkage and drying shrinkage) and the restrained stress were accelerated when the drying began; but the age when the drying began did not significantly influence the long-term shrinkage and restrained stress of HPC; the autogenous shrinkage stress continuously contributed to the development of the total restrained stress in HPC; the drying shrinkage stress developed very rapidly soon after the drying began; and the thermal stress was generated when the temperature dropped. The thermal stress was predominant at the early age, but the contributions of the three stresses to the total restrained stress were almost the same at the age of 56 d in this study. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 8835 KiB

Open AccessArticle

Verification of the Influence of Loading and Mortar Coating Thickness on Resistance to High Temperatures Due to Fire on Load-Bearing Masonries with Clay Tiles

by Rodrigo P. de Souza, Fernanda Pacheco, Gustavo L. Prager, Augusto M. Gil, Roberto Christ, Vinícius Muller de Mello and Bernardo F. Tutikian

Materials 2019, 12(22), 3669; https://doi.org/10.3390/ma12223669 - 07 Nov 2019

Cited by 5 | Viewed by 2339

Abstract

Masonry has been widely used as a construction method. However, there is a lack of information on its fire behavior due to the multitude of variables that could influence this method. This paper aimed to identify the influence of loading and mortar coating [...] Read more.

Masonry has been widely used as a construction method. However, there is a lack of information on its fire behavior due to the multitude of variables that could influence this method. This paper aimed to identify the influence of loading and mortar coating thickness on the fire behavior of masonry. Hence, six masonries made of clay tiles laid with mortar were evaluated. The mortar coating had a thickness of 25 mm on the face not exposed to high temperatures, while the fire-exposed face had thicknesses of 0, 15, and 25 mm. For each mortar coating thickness, two specimens were tested, with and without loading of 10 tf/m. The real-scale specimens were subjected to the standard ISO 834 fire curve for four hours, during which the properties of stability, airtightness, and thermal insulation were assessed. Results showed that loaded specimens yielded smaller deformations than unloaded ones. Samples that lacked mortar coating on the fire-exposed face underwent fire resistance decrease of 27.5%, while the ones with 15 mm decreased by 58.1%, and the ones with 25 mm decreased by 41.0%. As mortar coating thickness increased, the plane deformations decreased from 40 mm to 29 mm and the thermal insulation properties of the walls improved significantly. For specimens with mortar coating thickness of 25 mm, the load application resulted in a reduction of 23.8% of the thermal insulation, while the unloaded specimen showed a decrease of 43.3%, as well as a modification of its fire-resistance rating. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 3720 KiB

Open AccessArticle

Model for Predicting the Tortuosity of Transport Paths in Cement-Based Materials

by Tongning Cao, Lijuan Zhang, Guowen Sun, Caihui Wang, Ying Zhang, Na Yan and Aoxue Xu

Materials 2019, 12(21), 3623; https://doi.org/10.3390/ma12213623 - 04 Nov 2019

Cited by 9 | Viewed by 2224

Abstract

The tortuosity of the pore structure is an important factor affecting medium (water and harmful ions) transport in cement-based materials. In this study, a new tortuosity model was established to reveal the effect of aggregate size, morphology, and graded media on the transport [...] Read more.

The tortuosity of the pore structure is an important factor affecting medium (water and harmful ions) transport in cement-based materials. In this study, a new tortuosity model was established to reveal the effect of aggregate size, morphology, and graded media on the transport path in cement-based materials. Based on the stereological principle and the geometric algorithm, the distribution model of the ideal pebble and polygonal aggregate in cement-based materials was given first. Then, based on the image processing technology and MATLAB software, the morphology of the actual aggregate was also characterized to prove the similarity relationship between the ideal aggregate and actual aggregate. The reliability of the tortuosity model was verified by the mercury intrusion porosimetry test and data from other literature. Based on the tortuosity model, the influences of the aggregate particle shape parameters, hydration degree, and water-to-cement ratio on the tortuosity of the transport path were analyzed. Finally, the tortuosity model was further simplified to facilitate engineering application. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 8187 KiB

Open AccessArticle

The Effects of Nano-SiO₂ and Nano-TiO₂ Addition on the Durability and Deterioration of Concrete Subject to Freezing and Thawing Cycles

by Fang Liu, Tonghuan Zhang, Tao Luo, Mengzhen Zhou, Weiwei Ma and Kunkun Zhang

Materials 2019, 12(21), 3608; https://doi.org/10.3390/ma12213608 - 03 Nov 2019

Cited by 19 | Viewed by 2309

Abstract

The objective of this manuscript is to study the effects of nano-particle addition on the durability and internal deterioration of concrete subject to freezing and thawing cycles (FTCs). Fifteen nm of SiO₂, 30 nm of SiO₂, and 30 nm [...] Read more.

The objective of this manuscript is to study the effects of nano-particle addition on the durability and internal deterioration of concrete subject to freezing and thawing cycles (FTCs). Fifteen nm of SiO₂, 30 nm of SiO₂, and 30 nm of TiO₂ were added to concrete to prepare specimens with different contents. All the specimens were subjected to FTCs from 0 to 75. The mass of each specimen was measured once the FTCs reached 25, 50, and 75. Then the freezing and thawing resistance of the concrete was evaluated by computing the mass loss ratio. The pore fluid size distribution of the concrete was detected using nuclear magnetic resonance (NMR). The deterioration of the concrete subjected to FTCs was detected by industrial computed tomography (CT). The effect of different nano-particle sizes, different contents of nano-particles, and different types of nano-particles on the freezing and thawing resistance, the pore size, distribution, and the deterioration of the concrete were analyzed. The effects of FTCs on the pore size distribution and the internal deterioration of concrete were also studied. Compared to 30 nm-Nono-SiO₂ (NS), 15 nm-NS had a better effect in improving the internal structure for concrete, and 30 nm-Nano-TiO₂ (NT) also had a better effect in preventing pore and crack expansion. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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12 pages, 1626 KiB

Open AccessArticle

Influence of Cooling Methods on the Residual Mechanical Behavior of Fire-Exposed Concrete: An Experimental Study

by Espedito Felipe Teixeira de Carvalho, João Trajano da Silva Neto, Paulo Roberto Ribeiro Soares Junior, Priscila de Souza Maciel, Helder Luis Fransozo, Augusto Cesar da Silva Bezerra and Antônio Maria Claret de Gouveia

Materials 2019, 12(21), 3512; https://doi.org/10.3390/ma12213512 - 26 Oct 2019

Cited by 9 | Viewed by 2874

Abstract

This work reports the main conclusions of a study on the mechanical behavior of concrete under ISO 834 fire with different cooling methods. The aim of this research was to provide reliable data for the analysis of structures damaged by fire. The experimental [...] Read more.

This work reports the main conclusions of a study on the mechanical behavior of concrete under ISO 834 fire with different cooling methods. The aim of this research was to provide reliable data for the analysis of structures damaged by fire. The experimental program used cylindrical concrete test specimens subjected to ISO 834 heating in a furnace up to maximum gas temperatures of 400, 500, 600, 700, and 800 °C. The compressive strength was measured in three situations: (a) at the different temperature levels reached in the furnace; (b) after a natural cooling process; and (c) after aspersion with water at ambient temperature. The results indicate that the concrete residual compressive strength is fairly dependent on the maximum temperature reached in the furnace and revealed that concrete of a lower strength preserved relatively higher levels of strength. The cooling method significantly influenced the strength, albeit at a lower intensity. In all cases, the residual strength remained in the range of 38% to 67% of the strength at ambient temperature. The statistical analysis showed that the data obtained by the experimental program are significant and confirmed the influence of the conditions imposed on the residual strength. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 2935 KiB

Open AccessArticle

Physical Mechanism of Concrete Damage under Compression

by Hankun Liu, Xiaodan Ren, Shixue Liang and Jie Li

Materials 2019, 12(20), 3295; https://doi.org/10.3390/ma12203295 - 11 Oct 2019

Cited by 6 | Viewed by 2187

Abstract

Although considerable effort has been taken regarding concrete damage, the physical mechanism of concrete damage under compression remains unknown. This paper presents, for the first time, the physical reality of the damage of concrete under compression in the view of statistical and probabilistic [...] Read more.

Although considerable effort has been taken regarding concrete damage, the physical mechanism of concrete damage under compression remains unknown. This paper presents, for the first time, the physical reality of the damage of concrete under compression in the view of statistical and probabilistic information (SPI) at the mesoscale. To investigate the mesoscale compressive fracture, the confined force chain buckling model is proposed; using which the mesoscale parameters concerned could be directly from nanoindentation by random field theory. Then, the mesoscale parameters could also be identified from macro-testing using the stochastic damage model. In addition, the link between these two mesoscale parameters could be established by the relative entropy. A good agreement between them from nano- and macro- testing when the constraint factor approaches around 33, indicates that the mesoscale parameters in the stochastic damage model could be verified through the present research. Our results suggest that concrete damage is strongly dependent on the mesoscale random failure, where meso-randomness originates from intrinsic meso-inhomogeneity and meso-fracture arises physically from the buckling of the confined force chain system. The mesoscale random buckling of the confined force chain system above tends to constitute the physical mechanism of concrete damage under compression. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 18783 KiB

Open AccessArticle

Permeable Nanomontmorillonite and Fibre Reinforced Cementitious Binders

by Styliani Papatzani, Sotirios Grammatikos and Kevin Paine

Materials 2019, 12(19), 3245; https://doi.org/10.3390/ma12193245 - 04 Oct 2019

Cited by 10 | Viewed by 3258

Abstract

Clinker reduction in cementitious binders is of paramount importance today, and nanotechnology has extended permissible limits. In the present study, a reference binder consisting of 60% Portland cement, 20% limestone, 20% fly ash, 3% polyvinyl alcohol (PVA) fibres and 2% superplasticizer is optimized [...] Read more.

Clinker reduction in cementitious binders is of paramount importance today, and nanotechnology has extended permissible limits. In the present study, a reference binder consisting of 60% Portland cement, 20% limestone, 20% fly ash, 3% polyvinyl alcohol (PVA) fibres and 2% superplasticizer is optimized with three different types of nano-montmorillonite (nMt) dispersions; two organomodified ones and an inorganic one at different proportions (0.5% to 4%). Flexural strength, measured on day 7, 28, 56 and 90, was improved after day 28 with the addition of inorganic nMt. Thermal gravimetric analyses carried out on day 7, 28, 56 and 90 coupled with x-ray diffraction (at day 28) showed a distinctively enhanced pozzolanic reaction. Backscattered electron imaging confirmed changes in the microstructure. Late age relative density measurements of the nMt cementitious nanocomposites showed higher values than these of the reference paste, which can be attributed to better particle packing. Mercury intrusion porosimetry measurements give support to the optimal nMt dosage, being 1% by total mass of binder and water impermeability tests (modified with BS EN 492:2012) suggest that inorganic nMt can be a viable option material where permeability constitutes a prerequisite. Suggestions for further activation of the nMt-fibre reinforced cementitious nanocomposites were also made. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 4859 KiB

Open AccessArticle

Effect of Curing Condition on Resistance to Chloride Ingress in Concrete Using Ground Granulated Blast Furnace Slag

by JangHyun Park, Cheol Park, SungHyung Joh and HanSeung Lee

Materials 2019, 12(19), 3233; https://doi.org/10.3390/ma12193233 - 02 Oct 2019

Cited by 9 | Viewed by 2464

Abstract

Changes in the salt attack resistance of concrete using ground granulated blast furnace slag (GGBFS) were examined based on different curing conditions. These conditions were divided into air and underwater curing. Three concrete mixes with GGBFS replacement ratios of 0% (control group), 30% [...] Read more.

Changes in the salt attack resistance of concrete using ground granulated blast furnace slag (GGBFS) were examined based on different curing conditions. These conditions were divided into air and underwater curing. Three concrete mixes with GGBFS replacement ratios of 0% (control group), 30% and 60% were fabricated. Then, evaluation of concrete compressive strength, evaluation of chloride ion diffusion coefficient and electrochemical impedance spectroscopy (EIS) were performed. As the GGBFS replacement ratio increased, the concrete compressive strength of the air cured specimens decreased compared to the underwater cured specimens. With respect to the chloride ion diffusion coefficient measurements, the coefficient decreased as the GGBFS replacement ratio increased. However, the diffusion coefficient of the air cured specimen relative to the underwater cured ones increased up to two times. The EIS results showed that as the GGBFS replacement ratio increased, |Z| increased in every frequency range. However, the |Z| of the air cured specimen was lower than the underwater cured one. This showed the same tendency as the evaluation results of the chloride ion diffusion coefficient. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 1908 KiB

Open AccessArticle

Bending Load-Carrying Capacity of Reinforced Concrete Beams Subjected to Premature Failure

by Paolo Foraboschi

Materials 2019, 12(19), 3085; https://doi.org/10.3390/ma12193085 - 21 Sep 2019

Cited by 32 | Viewed by 4585

Abstract

This paper investigates the ultimate flexural strength of reinforced concrete beams when affected by premature failure due to a rotational capacity of the first plastic hinge being consumed before the last plastic hinges reach their maximum possible moment. The paper provides a simple [...] Read more.

This paper investigates the ultimate flexural strength of reinforced concrete beams when affected by premature failure due to a rotational capacity of the first plastic hinge being consumed before the last plastic hinges reach their maximum possible moment. The paper provides a simple formula for predicting the ultimate load of a hyperstatically supported beam, taking into account the available ductility. The proposed formula is the result of calibration against the ultimate loads from a non-linear analysis on a variety of beams, with a wide spectrum of configurations and with concrete grades from 10.0 to 60.0 N/mm². The formula in based on the plastic hinge model, making it easy to apply, and the ultimate bending moments allow for the actual rotational capacity, making predictions accurate. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 3873 KiB

Open AccessArticle

Mechanical and Fracture Properties of Fly Ash Geopolymer Concrete Addictive with Calcium Aluminate Cement

by Yamin Wang, Shaowei Hu and Zhen He

Materials 2019, 12(18), 2982; https://doi.org/10.3390/ma12182982 - 15 Sep 2019

Cited by 29 | Viewed by 2937

Abstract

In this paper, the mechanical and fracture properties of fly ash geopolymer concrete (FAGC) mixed with calcium aluminate cement (CAC) were explored. Fly ash was partially replaced by CAC with 2.5%, 5% and 7.5%. The results exhibit that the mechanical and fracture behaviors [...] Read more.

In this paper, the mechanical and fracture properties of fly ash geopolymer concrete (FAGC) mixed with calcium aluminate cement (CAC) were explored. Fly ash was partially replaced by CAC with 2.5%, 5% and 7.5%. The results exhibit that the mechanical and fracture behaviors of FAGC are significantly influenced by CAC content. Based on the formation of more aluminum-rich gels, C-(A)-S-H and C-S-H gels, with the increase of CAC content, the compressive strength, splitting tensile strength and elastic modulus improved. Meanwhile, the peak load and effective fracture toughness show a monotone increasing trend. In addition, because C-S-H gels absorbed more energy, the fracture energy of FAGC increases. The maximal peak load, double-K fracture toughness and fracture energy reached up to1.79 kN, 4.27 MPam^0.5, 10.1 MPam^0.5 and 85.8 N/m with CAC content of 7.5%, respectively. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 8201 KiB

Open AccessArticle

Study on the Fatigue and Durability Behavior of Structural Expanded Polystyrene Concretes

by Quan You, Linchang Miao, Chao Li, Huanglei Fang and Xiaodong Liang

Materials 2019, 12(18), 2882; https://doi.org/10.3390/ma12182882 - 06 Sep 2019

Cited by 3 | Viewed by 2496

Abstract

The fatigue and durability characteristics of structural expanded polystyrene concrete (EPS) are especially important when it was applied for structural elements in long-term service. In order to study the fatigue and durability behavior of structural EPS concrete, the long-term cyclic loading experiments and [...] Read more.

The fatigue and durability characteristics of structural expanded polystyrene concrete (EPS) are especially important when it was applied for structural elements in long-term service. In order to study the fatigue and durability behavior of structural EPS concrete, the long-term cyclic loading experiments and wetting–drying (W-D) cyclic experiments were conducted, respectively. The structural EPS concrete was found to have a relatively large damping and a fairly low dynamic elastic modulus under long-term cyclic load, which illustrated that it had a better energy absorption effect and toughness than plain concrete of the same strength level. Even if fine cracks appeared during the cyclic loading process, the relevant dynamic performance remained stable, which indicated that the structural EPS concrete had superior fatigue stability. In W-D cyclic experiments, the structural EPS concrete exhibited superior sulfate resistance. During the erosion test process, there was a positive correlation between the mass change and the evolution of the compressive strength of the structural EPS concrete, which indicated that Δm_B could be substituted for Δf to evaluate the degree of the structural EPS concrete eroded by sulfate attack. The study focuses on the fatigue performance and sulfate resistance of structural EPS concrete and is of important engineering value for promoting practical long-term operations. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 10774 KiB

Open AccessArticle

Research on the Improvement of Concrete Autogenous Self-healing Based on the Regulation of Cement Particle Size Distribution (PSD)

by Lianwang Yuan, Shuaishuai Chen, Shoude Wang, Yongbo Huang, Qingkuan Yang, Shuai Liu, Jinbang Wang, Peng Du, Xin Cheng and Zonghui Zhou

Materials 2019, 12(17), 2818; https://doi.org/10.3390/ma12172818 - 02 Sep 2019

Cited by 27 | Viewed by 3644

Abstract

Overgrinding of Portland cement brings excessive shrinkage and poor self-healing ability to concrete. In this paper, through the ultrasonic test and optical micrograph observation, the self-healing properties of concrete prepared by cement with different particle size distributions were studied. Besides, the effect of [...] Read more.

Overgrinding of Portland cement brings excessive shrinkage and poor self-healing ability to concrete. In this paper, through the ultrasonic test and optical micrograph observation, the self-healing properties of concrete prepared by cement with different particle size distributions were studied. Besides, the effect of carbonation and continued hydration on self-healing of concrete was analyzed. Results show that, for the Portland cement containing more particles with the size 30~60 μm, the concrete could achieve a better self-healing ability of concrete at 28 days. For the two methods to characterize the self-healing properties of concrete, the ultrasonic test is more accurate in characterizing the self-healing of internal crack than optical micrograph observation. The autogenous self-healing of concrete is jointly affected by the continued hydration and carbonation. At 7 days and 30 days, the autogenous self-healing of concrete is mainly controlled by the continued hydration and carbonation, respectively. The cement particle size could affect the continued hydration by affecting un-hydrated cement content and the carbonation by affecting the Ca(OH)₂ content. Therefore, a proper distribution of cement particle size, which brings a suitable amount of Ca(OH)₂ and un-hydrated cement, could improve the self-healing ability of concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 7055 KiB

Open AccessArticle

Temporal Acoustic Emission Index for Damage Monitoring of RC Structures Subjected to Bidirectional Seismic Loadings

by Chihab Abarkane, Francisco J. Rescalvo, Jesús Donaire-Ávila, David Galé-Lamuela, Amadeo Benavent-Climent and Antolino Gallego Molina

Materials 2019, 12(17), 2804; https://doi.org/10.3390/ma12172804 - 30 Aug 2019

Cited by 5 | Viewed by 2284

Abstract

This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing [...] Read more.

This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing ground acceleration until the final collapse. Each specimen was subjected to a different loading history. A relevant delay in the beginning of the significant AE energy is observed as the peak value of the ground acceleration increases. Based on this result, a new AE temporal damage index (TDI), defined as the time difference between the onset of the significant AE activity and the onset of the loading that causes this AE activity, is proposed and validated by comparing it with the plastic strain energy released by the concrete, typically used as a reliable damage level indicator. Good agreement was observed for both specimens and seismic inputs. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 3098 KiB

Open AccessArticle

Behavior of Rectangular-Sectional Steel Tubular Columns Filled with High-Strength Steel Fiber Reinforced Concrete Under Axial Compression

by Shiming Liu, Xinxin Ding, Xiaoke Li, Yongjian Liu and Shunbo Zhao

Materials 2019, 12(17), 2716; https://doi.org/10.3390/ma12172716 - 24 Aug 2019

Cited by 27 | Viewed by 3160

Abstract

This paper studies the effect of high-strength steel fiber reinforced concrete (SFRC) on the axial compression behavior of rectangular-sectional SFRC-filled steel tube columns. The purpose is to improve the integrated bearing capacity of these composite columns. Nine rectangular-sectional SFRC-filled steel tube columns and [...] Read more.

This paper studies the effect of high-strength steel fiber reinforced concrete (SFRC) on the axial compression behavior of rectangular-sectional SFRC-filled steel tube columns. The purpose is to improve the integrated bearing capacity of these composite columns. Nine rectangular-sectional SFRC-filled steel tube columns and one normal concrete-filled steel tube column were designed and tested under axial loading to failure. The compressive strength of concrete, the volume fraction of steel fiber, the type of internal longitudinal stiffener and the spacing of circular holes in perfobond rib were considered as the main parameters. The failure modes, axial load-deformation curves, energy dissipation capacity, axial bearing capacity, and ductility index are presented. The results identified that steel fiber delayed the local buckling of steel tube and increased the ductility and energy dissipation capacity of the columns when the volume fraction of steel fiber was not less than 0.8%. The longitudinal internal stiffening ribs and their type changed the failure modes of the local buckling of steel tube, and perfobond ribs increased the ductility and energy dissipation capacity to some degree. The compressive strength of SFRC failed to change the failure modes, but had a significant impact on the energy dissipation capacity, bearing capacity, and ductility. The predictive formulas for the bearing capacity and ductility index of rectangular-sectional SFRC-filled steel tube columns are proposed to be used in engineering practice. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 5814 KiB

Open AccessArticle

Physicochemical Study on the Strength Development Characteristics of Cold Weather Concrete Using a Nitrite–Nitrate Based Accelerator

by Heesup Choi, Masumi Inoue, Hyeonggil Choi, Jihoon Kim, Yuhji Sudoh, Sukmin Kwon, Bokyeong Lee and Akira Yoneyama

Materials 2019, 12(17), 2706; https://doi.org/10.3390/ma12172706 - 23 Aug 2019

Cited by 20 | Viewed by 3073

Abstract

There has recently been an increased use of anti-freezing agents that are primarily composed of salt- and alkali-free calcium nitrite (Ca(NO₂)₂) and calcium nitrate (Ca(NO₃)₂) to promote the hydration reaction of concrete in cold weather [...] Read more.

There has recently been an increased use of anti-freezing agents that are primarily composed of salt- and alkali-free calcium nitrite (Ca(NO₂)₂) and calcium nitrate (Ca(NO₃)₂) to promote the hydration reaction of concrete in cold weather concreting. Nitrite–nitrate based accelerators accelerate the hydration of C₃A and C₃S in cement more quickly when their quantities are increased, thereby boosting the concrete’s early strength and effectively preventing early frost damage. However, the connection between the hydrate formation behavior and the strength development characteristic over time has yet to be clearly identified. Therefore, in this study, a wide range of physicochemical reviews were carried out to clarify the relationship between the hydrate formation behavior and the strength development characteristics, both at an early age and at later ages, which results from the addition of nitrite–nitrate based accelerators to concrete in varying amounts. These accelerators also act as anti-freezing agents. The results show that an increased quantity of nitrite–nitrate based accelerators caused an increase in the early strength of the concrete. This was due to the formation of nitrite and nitrate hydrates in large amounts, in addition to ettringite containing SO₄², which is generated during the hydration reaction of normal Portland cement at an early age. On the other hand, at later ages, there was a rise in nitrite and nitrate hydrates with needle crystal structures exhibiting brittle fracture behavior. A decrease in C–S–H gel and Ca(OH)₂ hydrates, deemed to have caused a decline in strength on Day 3 and thereafter, was also observed. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 4668 KiB

Open AccessArticle

Effect of Fineness of Basaltic Volcanic Ash on Pozzolanic Reactivity, ASR Expansion and Drying Shrinkage of Blended Cement Mortars

by Kaffayatullah Khan, Muhammad Nasir Amin, Muhammad Umair Saleem, Hisham Jahangir Qureshi, Majdi Adel Al-Faiad and Muhammad Ghulam Qadir

Materials 2019, 12(16), 2603; https://doi.org/10.3390/ma12162603 - 15 Aug 2019

Cited by 29 | Viewed by 3706

Abstract

This study focuses on evaluating the effect of the fineness of basaltic volcanic ash (VA) on the engineering properties of cement pozzolan mixtures. In this study, VA of two different fineness, i.e., VA fine (VF) and VA ultra-fine (VUF) and commercially available fly [...] Read more.

This study focuses on evaluating the effect of the fineness of basaltic volcanic ash (VA) on the engineering properties of cement pozzolan mixtures. In this study, VA of two different fineness, i.e., VA fine (VF) and VA ultra-fine (VUF) and commercially available fly ash (FA) was used to partially replace cement. Including a control and a hybrid mix (10% each of VUF and FA), eleven mortar mixes were prepared with various percentages of VA and FA (10%, 20% and 30%) to partially replace cement. First, material characterization was performed by using X-ray florescence (XRF), X-ray powder diffraction (XRD), particle size analysis, and a modified Chappelle test. Then, the compressive strength development, alkali silica reactivity (ASR), and drying shrinkage of all mortar mixes were investigated. Finally, XRD analysis on paste samples of all mixes was performed to assess their pozzolanic reactivity at ages of 7 and 91 days. The results showed increased Chappelle reactivity values with an increase in the fineness of the VA. Mortars containing high percentages of VUF (20% and 30%) showed almost equal compressive strength compared to corresponding FA mortars at all ages, however, the hybrid mix (10% VUF + 10% FA) exhibited higher strength than that of the reference mix (100% cement), particularly, at 91 days. At low percentages (10%), ASR expansion in both VF and VUF mortars was higher compared to the corresponding FA mortar and the opposite behavior was observed at high percentages (20% and 30%). Among all the mixes including the control, mortar with VUF was found to be most effective in controlling drying shrinkages at all ages. The rate of consumption of calcium hydroxide (Ca(OH)₂) for pastes containing VUF and FA was almost the same, while VF showed low Ca(OH)₂ intensity. These results indicate that an increase in the fineness of VA significantly improvs performance, and therefore, it could be a feasible substitute for commercial admixtures in cement composites. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 7744 KiB

Open AccessArticle

Influence of Nano-SiO₂, Nano-CaCO₃ and Nano-Al₂O₃ on Rheological Properties of Cement–Fly Ash Paste

by Yiming Peng, Kunlin Ma, Guangcheng Long and Youjun Xie

Materials 2019, 12(16), 2598; https://doi.org/10.3390/ma12162598 - 15 Aug 2019

Cited by 27 | Viewed by 3026

Abstract

Rheological curves of cement–fly ash (C–FA) paste incorporating nanomaterials including nano-SiO₂ (NS), nano-CaCO₃ (NC) and nano-Al₂O₃ (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological [...] Read more.

Rheological curves of cement–fly ash (C–FA) paste incorporating nanomaterials including nano-SiO₂ (NS), nano-CaCO₃ (NC) and nano-Al₂O₃ (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel–Bulkley (H–B) model, and the influences of these nanomaterials on rheological properties of C–FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C–FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C–FA paste. When the content of NS and NA were 2 wt%, the rheological index of C–FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C–FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m²/g) and NA (120 m²/g) are much larger than that of NC (40 m²/g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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15 pages, 5115 KiB

Open AccessArticle

Properties and Reaction Mechanisms of Magnesium Phosphate Cement Mixed with Ferroaluminate Cement

by Liang Jia, Fangli Zhao, Jian Guo and Kai Yao

Materials 2019, 12(16), 2561; https://doi.org/10.3390/ma12162561 - 11 Aug 2019

Cited by 15 | Viewed by 2970

Abstract

A certain amount of ferroaluminate cement (FAC) was substituted for MgO during the magnesium phosphate cement (MPC) preparation to obtain the MPC–FAC composite cement. The influence of FAC on the strength, water resistance, pH, and setting time of MPC–FAC composite cement were examined. [...] Read more.

A certain amount of ferroaluminate cement (FAC) was substituted for MgO during the magnesium phosphate cement (MPC) preparation to obtain the MPC–FAC composite cement. The influence of FAC on the strength, water resistance, pH, and setting time of MPC–FAC composite cement were examined. The microstructure and chemical composition were also analyzed by adopting scanning electron microscopic energy-dispersive spectrometer and X-ray diffraction, respectively. The study showed that setting time of MPC–FAC composite cement was dramatically prolonged when FAC substitution for MgO was between 30 and 40 wt %. The strength of MPC–FAC did not decrease during the early curing time (1 h and 1 d), whereas it increased during the late curing time (3, 7, and 28 days). Moreover, the existence of FAC decreased the hydrated product K-struvite during the early curing time and thus dramatically enhanced the water-resistance of MPC–FAC. With the addition of FAC, a large number of cementitious materials of AFt and AFm, as well as flocculent colloidal substances of AH₃, C–S–H, and FH₃, were generated during the hydration of MPC, which were filled in the internal pore of the hydrate. Thus, the internal compactness of the sample increased, while the compact protective covering layer was generated on the surface to enhance the water resistance and strength in the late curing time. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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13 pages, 9476 KiB

Open AccessArticle

Mechanical Properties and Resistance to Acid Corrosion of Polymer Concrete Incorporating Ceramsite, Fly Ash and Glass Fibers

by Yinong Shen, Bo Liu, Jianfu Lv and Manlin Shen

Materials 2019, 12(15), 2441; https://doi.org/10.3390/ma12152441 - 31 Jul 2019

Cited by 14 | Viewed by 2929

Abstract

A novel polymer concrete (PC) using an aggregate of ceramsite, fly ash and glass fiber was created. Specimens were used in experiments to investigate its anticorrosion properties to determine the viability of its use in flue gas desulfurization (FGD) stacks. The inclusion of [...] Read more.

A novel polymer concrete (PC) using an aggregate of ceramsite, fly ash and glass fiber was created. Specimens were used in experiments to investigate its anticorrosion properties to determine the viability of its use in flue gas desulfurization (FGD) stacks. The inclusion of ceramsite reduces both the weight and the cost of the material. The effects of ceramsite and glass fiber on the flexural strength and compressive strength of the concrete were investigated. The experimental results showed that ceramsite reduces the flexural strength and the compressive strength of the concrete, but that the glass fiber increases both. Surface resistance to sulfuric acid corrosion and the microstructure of the corroded concrete were investigated. Specimens of the novel PC and the control PC strongly resisted acid corrosion. Although the specimen surfaces deteriorated, the interior structure of the PC was unaffected after 50 days of acid immersion. Processes by which sulfuric acid corrodes PC surfaces were determined. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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22 pages, 7752 KiB

Open AccessArticle

Effects of Modified Metakaolin Using Nano-Silica on the Mechanical Properties and Durability of Concrete

by Nasir Shafiq, Rabinder Kumar, Muhammad Zahid and Rana Faisal Tufail

Materials 2019, 12(14), 2291; https://doi.org/10.3390/ma12142291 - 17 Jul 2019

Cited by 44 | Viewed by 3767

Abstract

This paper discussed the effects of modified metakaolin (MK) with nano-silica (NS) on the mechanical properties and durability of concrete. In the first phase, trial mixes of concrete were prepared for achieving the desired value of the 28 days compressive strength, and the [...] Read more.

This paper discussed the effects of modified metakaolin (MK) with nano-silica (NS) on the mechanical properties and durability of concrete. In the first phase, trial mixes of concrete were prepared for achieving the desired value of the 28 days compressive strength, and the charge passed in rapid chloride permeability test (RCPT). In the second phase, statistical analysis was performed on the experimental results using the response surface method (RSM). The RSM was applied for optimizing the mix proportions for the required performance by exploiting the relationship between the mix characteristics and the corresponding test results. A blend of 10% MK + 1% NS as part of cement replacement exhibited the highest mechanical properties and durability characteristics of concrete; concrete mix showed that the 28-days compressive strength (CS) was 103 MPa, which was 15% greater than the CS of the control mix without MK or NS. The same mix showed more than 40% higher flexural and split-tensile strength than the control mix; also it resulted in a reduction of 73% in the rapid chloride permeability value. ANOVA technique was used for optimizing the nano-silica and metakaolin content for achieving maximum compressive strength and minimum RCPT value. Statistical analysis using ANOVA technique showed that the maximum compressive strength and lowest RCPT value could be achieved with a blend of 10% MK and 1.55% NS. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 2772 KiB

Open AccessArticle

Preparation and Reaction Mechanism Characterization of Alkali-activated Coal Gangue–Slag Materials

by Hongqiang Ma, Hongguang Zhu, Cheng Yi, Jingchong Fan, Hongyu Chen, Xiaonan Xu and Tao Wang

Materials 2019, 12(14), 2250; https://doi.org/10.3390/ma12142250 - 12 Jul 2019

Cited by 42 | Viewed by 3331

Abstract

In this paper, slag is used as a calcium source to make alkali-activated coal gangue–slag (AACGS) based material. The reaction mechanism of AACGS materials was discussed in depth by means of XRD, FT-IR, ²⁹Si MAS-NMR (nuclear magnetic resonance) and SEM-EDS (energy dispersive [...] Read more.

In this paper, slag is used as a calcium source to make alkali-activated coal gangue–slag (AACGS) based material. The reaction mechanism of AACGS materials was discussed in depth by means of XRD, FT-IR, ²⁹Si MAS-NMR (nuclear magnetic resonance) and SEM-EDS (energy dispersive spectrometer). The experimental results show that coal gangue can be used as a raw material for preparing alkali-activated materials. The liquid–solid ratio is the most influential factor on AACGS paste fluidity and strength, followed by slag content. As the modulus of sodium hydroxide increases, the depolymerization process of the reactant precursor is accelerated, but the high sodium hydroxide concentration inhibits the occurrence of the early coal gangue–slag polycondensation reaction, and exerts little effect on the 28 d compressive strength. Ca²⁺ in the slag promotes exchange with Na⁺, and the product is converted from N-A-S-H gel to C-(A)-S-H gel, and C-(A)-S-H is formed with higher Ca/Si ratio with the increase of slag content. The slight replacement of coal gangue by slag can greatly improve the reaction process and the strength of AACGS materials. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 3383 KiB

Open AccessArticle

Influence of BOF and GGBFS Based Alkali Activated Materials on the Properties of Porous Concrete

by Wen-Ten Kuo, Yi-Syuan Gao and Chuen-Ul Juang

Materials 2019, 12(14), 2214; https://doi.org/10.3390/ma12142214 - 10 Jul 2019

Cited by 8 | Viewed by 2647

Abstract

In this study, environmentally friendly ground granulated blast furnace slag (GGBFS) based alkali activated materials and basic oxygen furnace slags (BOFs) were used as bonding materials and aggregates, respectively, to produce novel, environmentally friendly GGBFS based porous concrete. Porous concrete with a particle [...] Read more.

In this study, environmentally friendly ground granulated blast furnace slag (GGBFS) based alkali activated materials and basic oxygen furnace slags (BOFs) were used as bonding materials and aggregates, respectively, to produce novel, environmentally friendly GGBFS based porous concrete. Porous concrete with a particle size of 4.75–9.5 mm and 9.5–19.00 mm was used as an aggregate. The “liquid-to-solid ratios” (L/S) variable was set at set at 0.5 and 0.6, and the “percentage of pore filling paste ratio” variable was controlled at 40%, 50%, and 60%. The curing period was set at 28 d, and the relationship between connected porosity and permeability, as well as that between unit weight and the pore filling paste ratio percentage were explored using analysis of variance. The results showed that the porous concrete had a maximum compressive strength of 8.31 MPa. The following results were obtained. An increase in percentage of pore filling paste ratio increased compressive strength. Permeability was measured at 4.67 cm/s and was positively correlated with porosity. An increase in porosity increased permeability, in which porosity was positively correlated with the percentage of pore filling paste ratio. The maximum splitting strength achieved during the 28 d was 1.46 MPa, showing a trend similar to that of compressive strength. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 4050 KiB

Open AccessArticle

Evaluation of Engineering Properties of Calcium Sulfoaluminate Cement-based Concretes Reinforced with Different Types of Fibers

by Vahid Afroughsabet, Luigi Biolzi and Sara Cattaneo

Materials 2019, 12(13), 2151; https://doi.org/10.3390/ma12132151 - 04 Jul 2019

Cited by 18 | Viewed by 3375

Abstract

Calcium sulfoaluminate (CSA) cement has recently gained increased attention due to its lower amount of CO₂ emissions, as compared to that of the ordinary Portland cement (OPC). This paper evaluates the impact of different types of fibers on the engineering features of [...] Read more.

Calcium sulfoaluminate (CSA) cement has recently gained increased attention due to its lower amount of CO₂ emissions, as compared to that of the ordinary Portland cement (OPC). This paper evaluates the impact of different types of fibers on the engineering features of CSA-based concretes at different water-cement ratios of 0.35 and 0.28. In this study, metallic fibers including double hooked-end steel fibers and hooked-end steel fibers, and non-metallic fibers (i.e., polyvinyl alcohol (PVA) fibers) were utilized at fiber content of 1%. The mechanical properties of concretes were assessed at different curing ages. Dimensional stability of the concrete mixes was also examined. The morphology of the fractured specimens was studied by using the SEM method. The results indicate that the engineering properties of concrete were improved by introducing fibers to the concrete, irrespective of fiber type. The results show that DHE steel fiber has an important effect on the flexural performance of CSA cement-based concretes and results in deflection-hardening behavior. It was observed that fibers and particularly PVA fibers cause a decrease in shrinkage deformation. Microstructure tests demonstrate that prismatic ettringite is the main hydration product of CSA cement-based concrete. The SEM observation also confirms that the inclusion of CSA cement in concrete improves the cohesiveness between the fibers and cement matrix. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 2876 KiB

Open AccessArticle

Research on Concrete Columns Reinforced with New Developed High-Strength Steel under Eccentric Loading

by Yonghui Hou, Shuangyin Cao, Xiangyong Ni and Yizhu Li

Materials 2019, 12(13), 2139; https://doi.org/10.3390/ma12132139 - 03 Jul 2019

Cited by 9 | Viewed by 4185

Abstract

The use of new developed high-strength steel in concrete members can reduce steel bar congestion and construction costs. This research aims to study the behavior of concrete columns reinforced with new developed high-strength steel under eccentric loading. Ten reinforced concrete columns were fabricated [...] Read more.

The use of new developed high-strength steel in concrete members can reduce steel bar congestion and construction costs. This research aims to study the behavior of concrete columns reinforced with new developed high-strength steel under eccentric loading. Ten reinforced concrete columns were fabricated and tested. The test variables were the transverse reinforcement amount and yield strength, eccentricity, and longitudinal reinforcement yield strength. The failure patterns were compression and tensile failure for columns subjected to small eccentricity and large eccentricity, respectively. The same level of post-peak deformability and ductility could only be obtained with a lower amount of transverse reinforcement when high-strength transverse reinforcements were used in columns subjected to small eccentricity. The high-strength longitudinal reinforcement improved the bearing capacity and post-peak deformability of the concrete columns. Furthermore, three different equivalent rectangular stress block (ERSB) parameters for predicting the bearing capacity of columns with high-strength steel are discussed based on test and simulated results. It is concluded that the China Code GB 50010-2010 overestimates the bearing capacity of columns with high-strength steel, whereas the bearing capacities computed using the America Code ACI 318-14 and Canada Code CSA A23.3-04 agree well with the test results. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 4643 KiB

Open AccessArticle

Investigating the Effects of Fiber Reinforced Concrete on the Performance of End-Zone of Pre-Stressed Beams

by Asif Jalal, Nasir Shafiq and Muhammad Zahid

Materials 2019, 12(13), 2093; https://doi.org/10.3390/ma12132093 - 28 Jun 2019

Cited by 3 | Viewed by 2954

Abstract

This paper presents the results of the behavior of end zone of post-tensioned (PT) beams made of fiber reinforced concrete (FRC). The principal aim of using FRC was to enhance the ductility and post-cracking behavior of end-zone of post-tensioned beams. A stronger and [...] Read more.

This paper presents the results of the behavior of end zone of post-tensioned (PT) beams made of fiber reinforced concrete (FRC). The principal aim of using FRC was to enhance the ductility and post-cracking behavior of end-zone of post-tensioned beams. A stronger and tougher end-zone of PT-beams is necessary when it is subjected to dynamic loading. Post-tensioned (PT) beams are typically used for the construction of bridges and industrial buildings, which are often subjected to vibrations and cyclic loading. Pre-mature cracking of the end zone (EZ) of a PT-beam is considered the type of problem that may cause the structural collapse. In this research program, polyvinyl alcohol (PVA) and copper-coated steel (CCS) fibers were used in concrete for improving the EZ performance of PT-beams. The use of FRC caused a 50% reduction in the shear reinforcement within the end zone of the PT-beam, which also avoided the congestion of steel in the end zone. Hence, the concrete was placed homogeneously, and smooth finished surfaces of the beams were obtained. FRC controlled the bursting of the end zone during the transfer of the full pre-stress force, and approximately 25% increment in the strain energy of the end zone was observed, which was also found efficient in strain diminution along the length of the beam. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 4759 KiB

Open AccessArticle

A DIC-Based Study on Compressive Responses of Concrete after Exposure to Elevated Temperatures

by Sheng Xiang, Lei Zeng, Jicheng Zhang, Juan Chen, Yanhua Liu, Guoyuan Cheng and Jinxu Mo

Materials 2019, 12(13), 2044; https://doi.org/10.3390/ma12132044 - 26 Jun 2019

Cited by 23 | Viewed by 3017

Abstract

This paper provides an experimental investigation on the cracking process and residual mechanical properties of concrete after exposure to elevated temperatures. A total of 36 standard concrete prism specimens were tested after exposure to high temperatures of up to 600 °C. The failure [...] Read more.

This paper provides an experimental investigation on the cracking process and residual mechanical properties of concrete after exposure to elevated temperatures. A total of 36 standard concrete prism specimens were tested after exposure to high temperatures of up to 600 °C. The failure modes, cracking process, residual mechanical properties, deformation characteristics and the strain distribution on the surface during the loading procedure were presented. The influences of exposure temperature and water–cement ratio (w/c) were interpreted. The digital image correlation (DIC) method was applied to quantitatively and visually characterize the development of cracking and relative displacement on the concrete surface. The findings suggest that the residual compressive strength and elastic modulus of the concrete decreases gradually with the increasing temperature, especially in the specimens with lower w/c ratio. The DIC technique provides an effective means to measure very precise and detailed information, including the crack opening and distribution of strain on the concrete surface. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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17 pages, 2569 KiB

Open AccessArticle

A Statistical Damage Constitutive Model Based on the Weibull Distribution for Alkali-Resistant Glass Fiber Reinforced Concrete

by Zhende Zhu, Cong Zhang, Songsong Meng, Zhenyue Shi, Shanzhi Tao and Duan Zhu

Materials 2019, 12(12), 1908; https://doi.org/10.3390/ma12121908 - 13 Jun 2019

Cited by 27 | Viewed by 3353

Abstract

The addition of alkali-resistant glass fiber to concrete effectively suppresses the damage evolution such as microcrack initiation, expansion, and nucleation and inhibits the development and penetration of microcracks, which is very important for the long-term stability and safety of concrete structures. We conducted [...] Read more.

The addition of alkali-resistant glass fiber to concrete effectively suppresses the damage evolution such as microcrack initiation, expansion, and nucleation and inhibits the development and penetration of microcracks, which is very important for the long-term stability and safety of concrete structures. We conducted indoor flat tensile tests to determine the occurrence and development of cracks in alkali-resistant glass fiber reinforced concrete (AR-GFRC). The composite material theory and Krajcinovic vector damage theory were used to correct the quantitative expressions of the fiber discontinuity and the elastic modulus of the concrete. The Weibull distribution function was used and an equation describing the damage evolution of the AR-GFRC was derived. The constitutive equation was validated using numerical parameter calculations based on the elastic modulus, the fiber content, and a performance test of polypropylene fiber. The results showed that the tensile strength and peak strength of the specimen were highest at a concrete fiber content of 1%. The changes in the macroscopic stress–strain curve of the AR-GFRC were determined and characterized by the model. The results of this study provide theoretical support and reference data to ensure safety and reliability for practical concrete engineering. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 3794 KiB

Open AccessArticle

Testing and Prediction of the Strength Development of Recycled-Aggregate Concrete with Large Particle Natural Aggregate

by Changyong Li, Fei Wang, Xiangsheng Deng, Yizhuo Li and Shunbo Zhao

Materials 2019, 12(12), 1891; https://doi.org/10.3390/ma12121891 - 12 Jun 2019

Cited by 18 | Viewed by 2678

Abstract

In this paper, a new recycled aggregate concrete (RAC) was produced with composite coarse aggregate and fine recycled aggregate. The composite coarse aggregate was mixed into continuous gradation by large particle natural aggregate with small particle recycled aggregate. To explore the time-dependent developments [...] Read more.

In this paper, a new recycled aggregate concrete (RAC) was produced with composite coarse aggregate and fine recycled aggregate. The composite coarse aggregate was mixed into continuous gradation by large particle natural aggregate with small particle recycled aggregate. To explore the time-dependent developments of the compressive strength and splitting tensile strength of this new RAC, 320 groups of cubic specimens were tested at different curing ages from 3 days to 360 days to measure the compressive and splitting tensile strengths. The amount of large particle natural aggregate varied from zero to 70% in mass of the total coarse aggregate. The water/cement ratio was taken as 0.60, 0.49, 0.41 and 0.36 to represent four strength grades of the RAC at about C20, C30, C40 and C50. Based on the tested results, the curves of the compressive and tensile strengths of the RAC that changed with curing age are plotted, which clearly exhibit that the amount of large particle natural aggregate had a rational range in different strength grades of the RAC which had better aging strength. When the RAC was no larger than C30 with a water/cement ratio of 0.60 and 0.49, the amount of large particle natural aggregate should be no more than 30%; when the RAC was no less than C40 with a water/cement ratio of 0.41 and 0.36, the amount of large particle natural aggregate should be no less than 50%. Along with the general prediction of the strength development of all the tested RAC, the optimal predictive formulas are proposed for the strength development of RAC with a rational amount of natural aggregate. Meanwhile, the strength developments of RAC with a rational amount of natural aggregate are assessed by the time-dependent models proposed by the ACI Committee 209 and CEB-FIP MC 2010. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 3798 KiB

Open AccessArticle

Study on Mix Proportion Optimization of Manufactured Sand RPC and Design Method of Steel Fiber Content under Different Curing Methods

by Chunling Zhong, Mo Liu, Yunlong Zhang and Jing Wang

Materials 2019, 12(11), 1845; https://doi.org/10.3390/ma12111845 - 06 Jun 2019

Cited by 14 | Viewed by 3032

Abstract

This study investigated four factors (water/binder ratio, silica fume, fly ash, and sand/binder ratio) using the orthogonal experimental design method to prepare the mix proportions of a manufactured sand reactive powder concrete (RPC) matrix to determine the optimal matrix mix proportions. On this [...] Read more.

This study investigated four factors (water/binder ratio, silica fume, fly ash, and sand/binder ratio) using the orthogonal experimental design method to prepare the mix proportions of a manufactured sand reactive powder concrete (RPC) matrix to determine the optimal matrix mix proportions. On this basis, we assessed the compressive and splitting tensile strengths of different steel fiber contents under natural, standard, and compound curing conditions to develop an economical and reasonable RPC for various engineering requirements. A calculation method for the RPC strength of the steel fiber contents was evaluated. The results showed that the optimum steel fiber content for manufactured sand RPC is 4% under natural, standard, and compound curing conditions. Compared with standard curing, compound curing can improve the early strength of manufactured sand RPC but only has a small effect on the enhancement of late strength. Although the strength of natural curing is slightly lower than that of standard curing, it basically meets project requirements and is beneficial for practical applications. The calculation formula of 28-day compressive and splitting tensile strengths of manufactured sand RPC steel fiber at 0%–4% is proposed to meet the different engineering requirements and the flexible selection of steel fiber content. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 10906 KiB

Open AccessArticle

Internal Curing Effect and Compressive Strength Calculation of Recycled Clay Brick Aggregate Concrete

by Feng Chen, Kai Wu, Lijian Ren, Jianan Xu and Huiming Zheng

Materials 2019, 12(11), 1815; https://doi.org/10.3390/ma12111815 - 04 Jun 2019

Cited by 28 | Viewed by 3231

Abstract

In order to investigate the internal curing effect of recycled brick aggregate (RBA) in recycled aggregate concrete (RAC) and calculate its contribution to the final compressive strength, two RAC groups with different recycled aggregates and 6 replacement ratios (r) under 4 [...] Read more.

In order to investigate the internal curing effect of recycled brick aggregate (RBA) in recycled aggregate concrete (RAC) and calculate its contribution to the final compressive strength, two RAC groups with different recycled aggregates and 6 replacement ratios (r) under 4 curing ages were tested. Results show that the compressive strengths of RACI and RACII decrease steadily with the increase of r when below 40%, and that there is a significant drop once the r is higher than 60%. The internal curing effect for RAC with a low RBA ratio is mainly reflected during the curing age of 14–21 days, while for RAC with a high RBA ratio, this internal curing effect appears earlier, during 7–14 days, and becomes very obvious after 14 days. In addition, the actual tested compressive strength of RAC replaced by 100% RBA exceeds around 40% of the expected compressive strength at the age of 28 days. When the age of RAC entirely with RBA is 28 days, the compressive strength caused by the internal curing effect accounts for around 28% of the actual tested compressive strength. The most appropriate r of RBA for RAC production is between 40% to 60%. Finally, the equations for calculating the compressive strength of RAC are presented considering the curing ages, the replacement ratios and the internal curing effect of RBA. Further, a unified equation is suggested for convenience in calculation. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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10 pages, 3457 KiB

Open AccessArticle

Physical Properties of Concrete Containing Graphene Oxide Nanosheets

by Yu-You Wu, Longxin Que, Zhaoyang Cui and Paul Lambert

Materials 2019, 12(10), 1707; https://doi.org/10.3390/ma12101707 - 26 May 2019

Cited by 48 | Viewed by 6150

Abstract

Concrete made from ordinary Portland cement is one of the most widely used construction materials due to its excellent compressive strength. However, concrete lacks ductility resulting in low tensile strength and flexural strength, and poor resistance to crack formation. Studies have demonstrated that [...] Read more.

Concrete made from ordinary Portland cement is one of the most widely used construction materials due to its excellent compressive strength. However, concrete lacks ductility resulting in low tensile strength and flexural strength, and poor resistance to crack formation. Studies have demonstrated that the addition of graphene oxide (GO) nanosheet can effectively enhance the compressive and flexural properties of ordinary Portland cement paste, confirming GO nanosheet as an excellent candidate for using as nano-reinforcement in cement-based composites. To date, the majority of studies have focused on cement pastes and mortars. Only limited investigations into concretes incorporating GO nanosheets have been reported. This paper presents an experimental investigation on the slump and physical properties of concrete reinforced with GO nanosheets at additions from 0.00% to 0.08% by weight of cement and a water–cement ratio of 0.5. The study demonstrates that the addition of GO nanosheets improves the compressive strength, flexural strength, and split tensile strength of concrete, whereas the slump of concrete decreases with increasing GO nanosheet content. The results also demonstrate that 0.03% by weight of cement is the optimum value of GO nanosheet dosage for improving the split tensile strength of concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 7285 KiB

Open AccessArticle

Bonding Behavior of Repair Material Using Fly-Ash/Ground Granulated Blast Furnace Slag-Based Geopolymer

by Wen-Ten Kuo, Ming-Yao Liu and Chuen-Ul Juang

Materials 2019, 12(10), 1697; https://doi.org/10.3390/ma12101697 - 24 May 2019

Cited by 19 | Viewed by 3748

Abstract

Fly ash/ground-granulated blast-furnace slag geopolymer (FGG) contains reaction products with a high volume of Ca, hydrated CaSiO₃, and hydrated AlCaSiO₃. These compounds enable the filling of large air voids in a structure, thus increasing compactness. Therefore, FGG is a [...] Read more.

Fly ash/ground-granulated blast-furnace slag geopolymer (FGG) contains reaction products with a high volume of Ca, hydrated CaSiO₃, and hydrated AlCaSiO₃. These compounds enable the filling of large air voids in a structure, thus increasing compactness. Therefore, FGG is a more effective repair material to stabilize structures and can function as a sealing and insulating layer. This study used FGG as the repair material for concrete with ground-granulated blast-furnace slag (GGBFS) as the main cement material. The bond strength of the repair was discussed from different aspects, including for fly-ash substitution rates of 0%, 10%, 20%, and 30% and for liquid–solid ratios of 0.4 and 0.5. The slant shear test, and the split tensile test were employed in this analysis. Moreover, acoustic emission (AE) and scanning electron microscopy were used to confirm the damage modes and microstructural characteristics of these repairs. The results revealed that when the liquid–solid ratio increased from 0.4 to 0.5, the slant shear strength of the repaired material decreased from 36.9 MPa to 33.8 MPa, and the split tensile strength decreased from 1.97 MPa to 1.87 MPa. The slant shear test and split tensile test demonstrated that the repair material exhibited the highest effectiveness when the fly-ash substitution was 10%, and revealed that the repair angle directly affected the damage modes. The AE technique revealed that the damage behavior pattern of the FGG repair material was similar to that of Portland concrete. The microstructural analysis revealed that the FGG–concrete interphase contained mostly hydration products, and based on energy-dispersive X-ray spectroscopy (EDX), the compactness in the interphase and bond strength increased after the polymerization between the geopolymer and concrete. This indicated that the geopolymer damage mode was highly related to the level of polymerization. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 6506 KiB

Open AccessArticle

Experimental Study on the Preparation of Recycled Admixtures by Using Construction and Demolition Waste

by Shujun Li, Qiuyi Li, Xiaolong Zhao, Jianlin Luo, Song Gao, Gongbing Yue and Dunlei Su

Materials 2019, 12(10), 1678; https://doi.org/10.3390/ma12101678 - 23 May 2019

Cited by 28 | Viewed by 3580

Abstract

The use of construction and demolition waste (CDW) to prepare recycled admixtures is of great significance for the complete resource reutilization of CDW. In this paper, different kinds of CDW were prepared into recycled powder (RP) with a specific particle size (0–45 µm [...] Read more.

The use of construction and demolition waste (CDW) to prepare recycled admixtures is of great significance for the complete resource reutilization of CDW. In this paper, different kinds of CDW were prepared into recycled powder (RP) with a specific particle size (0–45 µm or 0–75 µm). The fineness, water requirement ratio (WRR), fluidity, loss on ignition (LOI), strength activity index (SAI) and compatibility of cement and superplasticizer (CCS) were examined. The above test results were analyzed by advanced analysis tools, such as laser particle size analysis, XRD, XRF, DSC-TGA, SEM, and BET. The properties of different types of RPs varied greatly, which was closely related to the microstructure, particle morphology and chemical composition of the RP. The experimental results showed that all kinds of RPs after grinding had a high fineness and good particle size distribution, and the mineral composition was dominated by SiO₂ with the content exceeding 50%. The WRR of various RPs was between 105% and 112%, and the SAI was between 68% and 78%, but the LOI varied greatly. Different types of RPs had a negative impact on the CCS, but the compatibility of cement and naphthalene-based superplasticizer was less affected. The content of recycled brick powder (RBP) in a hybrid recycled powder (HRP) was an important factor. When the content of RBP in HRP exceeded 50%, the HRP could meet the basic performance requirements of fly ash. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 4315 KiB

Open AccessArticle

Characterization of Titanium Nanotube Reinforced Cementitious Composites: Mechanical Properties, Microstructure, and Hydration

by Hyeonseok Jee, Jaeyeon Park, Erfan Zalnezhad, Keunhong Jeong, Seung Min Woo, Seungwook Seok and Sungchul Bae

Materials 2019, 12(10), 1617; https://doi.org/10.3390/ma12101617 - 16 May 2019

Cited by 16 | Viewed by 2917

Abstract

In recent years, nano-reinforcing technologies for cementitious materials have attracted considerable interest as a viable solution for compensating the poor cracking resistance of these materials. In this study, for the first time, titanium nanotubes (TNTs) were incorporated in cement pastes and their effect [...] Read more.

In recent years, nano-reinforcing technologies for cementitious materials have attracted considerable interest as a viable solution for compensating the poor cracking resistance of these materials. In this study, for the first time, titanium nanotubes (TNTs) were incorporated in cement pastes and their effect on the mechanical properties, microstructure, and early-age hydration kinetics was investigated. Experimental results showed that both compressive (~12%) and flexural strength (~23%) were enhanced with the addition of 0.5 wt.% of TNTs relative to plain cement paste at 28 days of curing. Moreover, it was found that, while TNTs accelerated the hydration kinetics of the pure cement clinker phase (C₃S) in the early age of the reaction (within 24 h), there was no significant effect from adding TNTs on the hydration of ordinary Portland cement. TNTs appeared to compress the microstructure by filling the cement paste pore of sizes ranging from 10 to 100 nm. Furthermore, it could be clearly observed that the TNTs bridged the microcracks of cement paste. These results suggested that TNTs could be a great potential candidate since nano-reinforcing agents complement the shortcomings of cementitious materials. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 2214 KiB

Open AccessArticle

Nonlinear Creep Damage Constitutive Model of Concrete Based on Fractional Calculus Theory

by Cong Zhang, Zhende Zhu, Shu Zhu, Zhilei He, Duan Zhu, Jinzhong Liu and Songsong Meng

Materials 2019, 12(9), 1505; https://doi.org/10.3390/ma12091505 - 08 May 2019

Cited by 33 | Viewed by 3610

Abstract

Concrete creep has become one of the major problems that threatens concrete structural development and construction. However, a reasonable and accurate calculation model for numerical analysis is the key to control and solve the creep deformation of concrete. To better describe the concrete [...] Read more.

Concrete creep has become one of the major problems that threatens concrete structural development and construction. However, a reasonable and accurate calculation model for numerical analysis is the key to control and solve the creep deformation of concrete. To better describe the concrete nonlinear creep damage evolution rule, the visco-elasticity Plasticity Rheological Theory, Riemann Liouville Theory and Combined Model Theory are quoted, and the Able dashpot is used to reconstruct fractional-order soft-body composite elements to propose the expression of the stress-strain relationship of the elastomer, visco-elasticity plasticity body, and Viscoplasticity body, considering the evolution of the concrete compression damage process. A nonlinear creep damage constitutive model of concrete, based on fractional calculus theory, is conducted, and the parameters of the specific calculation method of the model are given. The influence of stress level σ, fractional order n and material parameter α on the concrete creep process is determined by a sensitivity analysis of the model parameters. The creep process and deformation amount of concrete in practical engineering can be effectively controlled by the results of the proposed sensitivity analysis. The research results can be used to provide guidance and reference for the safe construction of concrete engineering in actual practice. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 13885 KiB

Open AccessArticle

Evaluation of Carbon Nanotube Incorporation in Cementitious Composite Materials

by Ana Catarina Jorge Evangelista, Jorge Fernandes de Morais, Vivian Tam, Mahfooz Soomro, Leandro Torres Di Gregorio and Assed N. Haddad

Materials 2019, 12(9), 1504; https://doi.org/10.3390/ma12091504 - 08 May 2019

Cited by 17 | Viewed by 3197

Abstract

Over the last decades, new materials with outstanding performance have been introduced in the construction industry. Considering these new technologies, it is worth mentioning that nanotechnology has revolutionized various areas of engineering. In the area of civil engineering and construction, cement is used [...] Read more.

Over the last decades, new materials with outstanding performance have been introduced in the construction industry. Considering these new technologies, it is worth mentioning that nanotechnology has revolutionized various areas of engineering. In the area of civil engineering and construction, cement is used for various purposes and the search to improve its performance has been receiving growing interest within the scientific community. The objective of this research was to evaluate the behavior of cement mortar produced by the addition of multi-walled carbon nanotubes (MWCNTs) in different concentrations by comparing their physical and mechanical properties with the properties of the nanotube-free composite. Motivated by the lack of consensus in the literature concerning to the optimal dosage of CNTs in cementitious matrices, three different carbon nanotube ratios, 0.20, 0.40 and 0.60 wt % Portland cement, were investigated with the aim of evaluating the mechanical properties. Destructive tests were carried out to determine the compressive strength, flexural strength and split tensile strength. Additionally, a non-destructive test was performed to determine the dynamic elastic modulus and density. Scanning electron microscopy (SEM) images showed the interaction between the MWCNTs and the hydration products of Portland cement mortar. The results indicated the potential contribution of 0.40 wt % cement CNTs to the enhancement of the mechanical properties of the cement composite as a promising construction material. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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22 pages, 4292 KiB

Open AccessArticle

Mechanical Properties and Seismic Performance of Wood-Concrete Composite Blocks for Building Construction

by David Dominguez-Santos, Daniel Mora-Melia, Gonzalo Pincheira-Orellana, Pablo Ballesteros-Pérez and Cesar Retamal-Bravo

Materials 2019, 12(9), 1500; https://doi.org/10.3390/ma12091500 - 08 May 2019

Cited by 13 | Viewed by 5378

Abstract

Recent catastrophes that occurred during seismic events suggest the importance of developing new seismic-resistant materials for use in building construction. Ordinary concrete is one of the most common materials in buildings. However, due to its low ductility and flexural strength, its seismic behavior [...] Read more.

Recent catastrophes that occurred during seismic events suggest the importance of developing new seismic-resistant materials for use in building construction. Ordinary concrete is one of the most common materials in buildings. However, due to its low ductility and flexural strength, its seismic behavior can be improved upon by different additives. In this regard, wood-concrete composites exhibit desirable structural properties not achievable by either wood or concrete alone, making it an interesting material from a seismic point of view. This work analyzes and compares the performance of blocks built with ordinary concrete versus blocks built using different wood additives (sawdust and wood shavings). This includes the construction of concrete blocks in a lab, determination of their construction and seismic-resistant properties, as well as an analysis of their performance in buildings with a different number of storeys. The results show how blocks with wood aggregates comply with current regulations for structural materials in a seismic country like Chile, while also considerably outperforming traditional concrete blocks in the event of an earthquake. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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21 pages, 1990 KiB

Open AccessArticle

Numerical Study on Concrete Pumping Behavior via Local Flow Simulation with Discrete Element Method

by Yijian Zhan, Jian Gong, Yulin Huang, Chong Shi, Zibo Zuo and Yiqun Chen

Materials 2019, 12(9), 1415; https://doi.org/10.3390/ma12091415 - 30 Apr 2019

Cited by 24 | Viewed by 4136

Abstract

The use of self-consolidating concrete and advanced pumping system enables efficient construction of super high-rise buildings; however, risks such as clogging or even bursting of pipeline still exist. To better understand the fresh concrete pumping mechanisms in detail, the discrete element method is [...] Read more.

The use of self-consolidating concrete and advanced pumping system enables efficient construction of super high-rise buildings; however, risks such as clogging or even bursting of pipeline still exist. To better understand the fresh concrete pumping mechanisms in detail, the discrete element method is employed in this paper for the numerical simulation of local pumping problems. By modeling the coarse aggregates as rigid clumps and appropriately defining the contact models, the concrete flow in representative pipeline units is well revealed. Important factors related to the pipe geometry, aggregate geometry and pumping condition were considered during a series of parametric studies. Based on the simulation results, their impact on the local pumping performance is summarized. The present work demonstrates that the discrete element simulation offers a useful way to evaluate the influence of various parameters on the pumpability of fresh concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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27 pages, 4183 KiB

Open AccessArticle

Designing the Composition of Cement Stabilized Rammed Earth Using Artificial Neural Networks

by Hubert Anysz and Piotr Narloch

Materials 2019, 12(9), 1396; https://doi.org/10.3390/ma12091396 - 29 Apr 2019

Cited by 41 | Viewed by 9201

Abstract

Cement stabilized rammed earth (CRSE) is a sustainable, low energy consuming construction technique which utilizes inorganic soil, usually taken directly from the construction site, with a small addition of Portland cement as a building material. This technology is gaining popularity in various regions [...] Read more.

Cement stabilized rammed earth (CRSE) is a sustainable, low energy consuming construction technique which utilizes inorganic soil, usually taken directly from the construction site, with a small addition of Portland cement as a building material. This technology is gaining popularity in various regions of the world, however, there are no uniform standards for designing the composition of the CSRE mixture. The main goal of this article is to propose a complete algorithm for designing CSRE with the use of subsoil obtained from the construction site. The article’s authors propose the use of artificial neural networks (ANN) to determine the proper proportions of soil, cement, and water in a CSRE mixture that provides sufficient compressive strength. The secondary purpose of the paper (supporting the main goal) is to prove that artificial neural networks are suitable for designing CSRE mixtures. For this purpose, compressive strength was tested on several hundred CSRE samples, with different particle sizes, cement content and water additions. The input database was large enough to enable the artificial neural network to produce predictions of high accuracy. The developed algorithm allows us to determine, using relatively simple soil tests, the composition of the mixture ensuring compressive strength at a level that allows the use of this material in construction. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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16 pages, 2436 KiB

Open AccessArticle

Basic Properties of Calcined Underground Ant Nest Materials and Its Influence on the Compressive Strength of Concrete

by Wei Zhou, Peng Zhu and Wenjun Qu

Materials 2019, 12(7), 1191; https://doi.org/10.3390/ma12071191 - 11 Apr 2019

Cited by 6 | Viewed by 3560

Abstract

Underground ant nests are typically made of soil and rubble mixed with dead plant bodies, ant secretions, and other organic substances. The clay content is high, and the natural clay materials show pozzolanic activity after calcination. In this study, the underground ant nest [...] Read more.

Underground ant nests are typically made of soil and rubble mixed with dead plant bodies, ant secretions, and other organic substances. The clay content is high, and the natural clay materials show pozzolanic activity after calcination. In this study, the underground ant nest materials of Iridomyrmex anceps, which is a common ant in the Shanghai area, are calcined and ground, and the material properties of calcined ant nest clay powder (CANCP) are characterized from six aspects: chemical composition, particle morphology, specific gravity, specific surface area, particle size distribution and pozzolanic activity index. The pozzolanic activity of CANCP is evaluated by the strength contribution rate of pozzolanic activity, revealing that CANCP is beneficial to the strength of the mortar system from an early age. The influence of CANCP on the compressive strength of concrete is analyzed using three aspects, namely, content, curing age and calcination temperature, and it is found that the three aspects of CANCP have a strong influence on the compressive strength of concrete. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 7505 KiB

Open AccessArticle

The Influence of Water/Cement Ratio and Air Entrainment on the Electric Resistivity of Ionically Conductive Mortar

by Ruohong Zhao, Yubin Weng, Christopher Y. Tuan and An Xu

Materials 2019, 12(7), 1125; https://doi.org/10.3390/ma12071125 - 05 Apr 2019

Cited by 12 | Viewed by 3547

Abstract

Ionically-conductive mortar can be used for indoor radiant heating partition walls. In these applications, mortar blocks are soaked in electrolyte solutions of CuSO₄. The surfaces of the block are coated with sealant and epoxy resin afterwards to prevent evaporation. The mortar [...] Read more.

Ionically-conductive mortar can be used for indoor radiant heating partition walls. In these applications, mortar blocks are soaked in electrolyte solutions of CuSO₄. The surfaces of the block are coated with sealant and epoxy resin afterwards to prevent evaporation. The mortar block becomes a heating element due to ionic conduction if a voltage is applied to the electrodes in the block. Its electrical conductivity depends on the dispersion of the electrolyte, and hence on the porosity of the mortar. The test specimens in this study were divided into four groups according to the different air entrainment agents, including aluminum powder and hydrogen peroxide as well as two air-entraining agents, SJ-2 and K12. Each group was manufactured with water/cement ratios in the range of 0.5 to 0.9. The test results showed that the conductivity of the mortar was strongly influenced by the air-entrainment and the water cement ratios. The volumetric electric resistivity and the associated microstructures of the mortar were investigated. The test results showed that the specimens made with aluminum powder and a water–cement ratio of 0.65–0.75 had high porosity. The porosity of those specimens was further increased by adding two different air-entraining agents. The specimens with aluminum powder and SJ-2, along with a water–cement ratio of 0.7 appeared to be the optimum mixture. Its resistivity was 19.37 Ω·m at 28 days under 25.31% porosity. The experimental results indicate that an ionically-conductive mortar can be produced by combining different air-entrainment agents with variable water-cement ratios to meet a specified electrical heating requirement. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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14 pages, 4335 KiB

Open AccessArticle

Use of Ladle Furnace Slag and Other Industrial By-Products to Encapsulate Chloride in Municipal Solid Waste Incineration Fly Ash

by Ying Wang, Wen Ni and Prannoy Suraneni

Materials 2019, 12(6), 925; https://doi.org/10.3390/ma12060925 - 20 Mar 2019

Cited by 10 | Viewed by 3359

Abstract

Municipal solid waste incineration fly ash (MSWIFA) is a hazardous by-product of waste incineration. The objective of this research is to encapsulate the chloride in MSWIFA and to develop a utilizable construction material using MSWIFA, ground granulated blast-furnace slag (GGBFS), ladle furnace slag [...] Read more.

Municipal solid waste incineration fly ash (MSWIFA) is a hazardous by-product of waste incineration. The objective of this research is to encapsulate the chloride in MSWIFA and to develop a utilizable construction material using MSWIFA, ground granulated blast-furnace slag (GGBFS), ladle furnace slag (LFS), and gypsum. A secondary objective of the work is to explain the hydration and encapsulation mechanisms in this material system using isothermal calorimetry (IC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and ion chromatography (IC). The predominant hydration products are ettringite, Friedel’s salt, and C-S-H gel, with Friedel’s salt and C-S-H dominating in systems high in LFS and ettringite and C-S-H gel dominating in systems low in LFS. The chloride encapsulation showed a strong correlation with the Friedel’s salt amount; however, some encapsulation was also likely due to physical binding in the C-S-H gel. In a system with 30% MSWIFA (by mass), the optimal amount of LFS for strength and chloride encapsulation is 20%–40% (by mass). Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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Review

Jump to: Research

26 pages, 11076 KiB

Open AccessReview

Effects of Graphite on Electrically Conductive Cementitious Composite Properties: A Review

by Ting Luo and Qiang Wang

Materials 2021, 14(17), 4798; https://doi.org/10.3390/ma14174798 - 24 Aug 2021

Cited by 12 | Viewed by 3098

Abstract

Electrically conductive cementitious composites (ECCCs) have been widely used to complete functional and smart construction projects. Graphite, due to its low cost and wide availability, is a promising electrically conductive filler to generate electrically conductive networks in cement matrixes. Cement-based materials provide an [...] Read more.

Electrically conductive cementitious composites (ECCCs) have been widely used to complete functional and smart construction projects. Graphite, due to its low cost and wide availability, is a promising electrically conductive filler to generate electrically conductive networks in cement matrixes. Cement-based materials provide an ideal balance of safety, environmental protection, strength, durability, and economy. Today, graphite is commonly applied in traditional cementitious materials. This paper reviews previous studies regarding the effects and correlations of the use of graphite-based materials as conductive fillers on the properties of traditional cementitious materials. The dispersion, workability, cement hydration, mechanical strength, durability, and electrically conductive mechanisms of cementitious composites modified with graphite are summarized. Graphite composite modification methods and testing methods for the electrical conductivity of ECCCs are also summarized. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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18 pages, 2422 KiB

Open AccessReview

Lateral Formwork Pressure for Self-Compacting Concrete—A Review of Prediction Models and Monitoring Technologies

by Yaser Gamil, Jonny Nilimaa, Mats Emborg and Andrzej Cwirzen

Materials 2021, 14(16), 4767; https://doi.org/10.3390/ma14164767 - 23 Aug 2021

Cited by 11 | Viewed by 2805

Abstract

The maximum amount of lateral formwork pressure exerted by self-compacting concrete is essential to design a technically correct, cost-effective, safe, and robust formwork. A common practice of designing formwork is primarily based on using the hydrostatic pressure. However, several studies have proven that [...] Read more.

The maximum amount of lateral formwork pressure exerted by self-compacting concrete is essential to design a technically correct, cost-effective, safe, and robust formwork. A common practice of designing formwork is primarily based on using the hydrostatic pressure. However, several studies have proven that the maximum pressure is lower, thus potentially enabling a reduction in the cost of formwork by, for example, optimizing the casting rate. This article reviews the current knowledge regarding formwork pressure, parameters affecting the maximum pressure, prediction models, monitoring technologies and test setups. The currently used pressure predicting models require further improvement to consider several pressures influencing parameters, including parameters related to fresh and mature material properties, mix design and casting methods. This study found that the maximum pressure is significantly affected by the concretes’ structural build-up at rest, which depends on concrete rheology, temperature, hydration rate and setting time. The review indicates a need for more in-depth studies. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 5574 KiB

Open AccessReview

Recycling of Waste Materials for Asphalt Concrete and Bitumen: A Review

by Md Tareq Rahman, Abbas Mohajerani and Filippo Giustozzi

Materials 2020, 13(7), 1495; https://doi.org/10.3390/ma13071495 - 25 Mar 2020

Cited by 98 | Viewed by 14358

Abstract

Waste management has become an issue of increasing concern worldwide. These products are filling landfills and reducing the amount of livable space. Leachate produced from landfills contaminates the surrounding environment. The conventional incineration process releases toxic airborne fumes into the atmosphere. Researchers are [...] Read more.

Waste management has become an issue of increasing concern worldwide. These products are filling landfills and reducing the amount of livable space. Leachate produced from landfills contaminates the surrounding environment. The conventional incineration process releases toxic airborne fumes into the atmosphere. Researchers are working continuously to explore sustainable ways to manage and recycle waste materials. Recycling and reuse are the most efficient methods in waste management. The pavement industry is one promising sector, as different sorts of waste are being recycled into asphalt concrete and bitumen. This paper provides an overview of some promising waste products like high-density polyethylene, marble quarry waste, building demolition waste, ground tire rubber, cooking oil, palm oil fuel ash, coconut, sisal, cellulose and polyester fiber, starch, plastic bottles, waste glass, waste brick, waste ceramic, waste fly ash, and cigarette butts, and their use in asphalt concrete and bitumen. Many experts have investigated these waste materials and tried to find ways to use this waste for asphalt concrete and bitumen. In this paper, the outcomes from some significant research have been analyzed, and the scope for further investigation is discussed. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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20 pages, 8895 KiB

Open AccessReview

Role of Polypropylene Fibres in Concrete Spalling Risk Mitigation in Fire and Test Methods of Fibres Effectiveness Evaluation

by Izabela Hager and Katarzyna Mróz

Materials 2019, 12(23), 3869; https://doi.org/10.3390/ma12233869 - 23 Nov 2019

Cited by 21 | Viewed by 3617

Abstract

The explosive behaviour of concrete in fire is observed in rapidly heated concrete. The main factors controlling the occurrence of spalling are related to the material’s low porosity and high density as well as the limited ability to transport gases and liquids. Thus, [...] Read more.

The explosive behaviour of concrete in fire is observed in rapidly heated concrete. The main factors controlling the occurrence of spalling are related to the material’s low porosity and high density as well as the limited ability to transport gases and liquids. Thus, for high-strength, ultrahigh-strength, and reactive powder concrete, the risk of spalling is much higher than for normal-strength concrete. The paper presents the discussion on the leading hypothesis concerning the occurrence of concrete spalling. Moreover, the methods for spalling prevention, such as polypropylene fibre application, which has been found to be an effective technological solution for preventing the occurrence of spalling, are presented. Various tests and testing protocols are used to screen concrete mixes propensity toward spalling and to evaluate the polypropylene fibres’ effectiveness in spalling risk mitigation. The most effective testing methods were selected and their advantages were presented in the paper. The review was based mainly on the authors’ experiences regarding high performance concrete, reactive powder concrete testing, and observations on the effect of polypropylene fibres on material behaviour at high temperature. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 3564 KiB

Open AccessReview

Impacts of Low Atmospheric Pressure on Properties of Cement Concrete in Plateau Areas: A Literature Review

by Jinyang Huo, Zhenjun Wang, Huaxin Chen and Rui He

Materials 2019, 12(9), 1384; https://doi.org/10.3390/ma12091384 - 28 Apr 2019

Cited by 30 | Viewed by 3419

Abstract

Low atmospheric pressure (LAP) can enormously affect properties of cement concrete in plateau areas. There are fewer studies and attendances on this issue than those of cement concrete in normal atmospheric pressure (AP), because of the limitations of both environmental conditions and instruments. [...] Read more.

Low atmospheric pressure (LAP) can enormously affect properties of cement concrete in plateau areas. There are fewer studies and attendances on this issue than those of cement concrete in normal atmospheric pressure (AP), because of the limitations of both environmental conditions and instruments. In order to improve properties of cement concrete under LAP, influences of LAP on properties of cement concrete were reviewed in this work. The influence rules and mechanism on properties of cement concrete were summarized. The corresponding mechanism and techniques were put forward for enhancing the properties of cement concrete. The results of researchers show that LAP can significantly reduce the air entraining ability of the air entraining agent (AEA). Air content in concrete linearly decreases with the decrease of AP when other conditions are constant. If the initial air content is high, the decrease rate of air content increases with the decrease of AP. When the initial air content in cement concretes is similar, the greater the slump of cement concrete, the stronger its resistance to the decrease of air content caused by the decrease of AP. In addition, the condition of the bubble characteristics of hardened cement concrete under LAP is worse than that under normal AP. Therefore, the change of concrete properties under LAP is mainly attributed to these bubble characteristics, such as air content, bubble spacing coefficient, bubble radius and bubble specific surface area. In this work, nano-silica (negative charges) with cationic oligomeric surfactants is recommended as a new type of AEA to optimize the bubble characteristics under LAP in plateau areas. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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