Research

20 pages, 7925 KiB

Open AccessArticle

Gray Model Study of Strength and Pore Structure of Recycled Concrete Powder (RCP) Concrete Based on Low-Field NMR Technology

by Yongli Hou, Zhengxing Yu, Jianhua Zhang, Hongrui Yang and Weiqing Song

Materials 2023, 16(17), 6058; https://doi.org/10.3390/ma16176058 - 04 Sep 2023

Cited by 2 | Viewed by 1044

Abstract

In order to improve the resource utilization of recycled concrete powder (RCP), this study aimed to investigate the effect of RCP admixture, curing age, and alkali excitation on the strength of RCP concrete. In addition, the pore structure characteristics of RCP concrete were [...] Read more.

In order to improve the resource utilization of recycled concrete powder (RCP), this study aimed to investigate the effect of RCP admixture, curing age, and alkali excitation on the strength of RCP concrete. In addition, the pore structure characteristics of RCP concrete were analyzed in combination with low-field NMR. Furthermore, a gray predictive GM (1, 4) model was established to predict the mechanical properties of the concrete based on the pore structure parameters, especially the compressive and flexural tensile strengths. The results of the study indicate that the mechanical properties, namely compressive strength and flexural strength, of RCP concrete exhibit an initial increase followed by a subsequent decrease with increasing RCP content at 3 d, 7 d, and 28 d curing ages. In particular, the concrete exhibits the highest mechanical properties when the RCP content reaches 10%. As the curing age increases, the RCP gradually achieves full hydration, resulting in further refinement of the concrete pores and a denser structure, which subsequently improves the mechanical properties. In addition, the strength growth rate of alkali-excited recycled concrete (ARC) showed a continuous increase, indicating that alkali excitation increasingly improved the mechanical properties of the concrete. Furthermore, the study accurately predicted the mechanical properties of RCP concrete by using GM (1, 4) prediction models for its compressive strength and flexural tensile strength using pore characteristic parameters. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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13 pages, 7860 KiB

Open AccessArticle

Study on the Deterioration Mechanism of Magnesium Oxychloride Cement under an Alkaline Environment

by Lingyun An, Chenggong Chang, Fengyun Yan and Jianhong Peng

Materials 2023, 16(17), 5924; https://doi.org/10.3390/ma16175924 - 30 Aug 2023

Cited by 1 | Viewed by 673

Abstract

The deterioration process and deterioration mechanism of magnesium oxychloride cement (MOC) in an alkaline environment were studied using a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a Fourier transform infrared spectrometer (FT-IR) and a micro-electro-hydraulic servo pressure testing machine to investigate the [...] Read more.

The deterioration process and deterioration mechanism of magnesium oxychloride cement (MOC) in an alkaline environment were studied using a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a Fourier transform infrared spectrometer (FT-IR) and a micro-electro-hydraulic servo pressure testing machine to investigate the effects of soaking time in 10 wt.% NaOH solution on the macro- and micro-morphology, phase composition and compressive strength of MOC samples. The results show that the deterioration of MOC samples under an alkaline environment is mainly caused by the alkaline environment providing more OH⁻ ions, which can react with 5Mg(OH)₂·MgCl₂·8H₂O (P 5) in the sample. The resulting reaction gives rise to a faster decomposition of 5Mg(OH)₂·MgCl₂·8H₂O (P 5) and a substantial reduction in the strength of the sample, and finally leads to a gradual deterioration of MOC samples. Meanwhile, immersion time exhibits a significant effect on MOC samples. The extension of immersion time coincides with more OH⁻ ions entering the sample, and the greater presence of OH ions increases the likelihood that more P 5 will produce a hydrolysis reaction, further resulting in the increased deterioration of the sample. After soaking for 6 h in alkaline media, the main phase composition of the surface layer of an MOC sample changes to MgO and Mg(OH)₂, and its microscopic morphology is also dominated by round sheets, giving rise to a sharp decrease in its compressive strength (52.2%). When the immersion time is prolonged to 72 h, OH⁻ ions have already immersed into the inner core of the sample, causing the disappearance of P 5 from the whole sample. At the same time, both the surface and inner core of the sample exhibit a disc-shaped morphology, and chalking phenomena also appear on the surface of the sample. This reduces the compressive strength of the sample to 13.5 MPa, only 20% of its compressive strength in water. The compressive strength of the sample after 120 h of immersion is as low as 8.6 MPa, which is lower than that of the sample dipped in water for 21 days (9.5 MPa). As a result, the MOC samples studied in alkaline environments exhibit a faster deterioration rate, mainly because of a faster hydrolysis reaction by P 5, caused by more OH⁻ ions. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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15 pages, 4120 KiB

Open AccessArticle

Effect of Replacing Fine Aggregate with Fly Ash on the Performance of Mortar

by Dongsheng Zhang, Shuxiang Zhang and Qiuning Yang

Materials 2023, 16(12), 4292; https://doi.org/10.3390/ma16124292 - 09 Jun 2023

Cited by 1 | Viewed by 1180

Abstract

Natural river sand resources are facing depletion, and large-scale mining pollutes the environment and harms humans. To utilize fly ash fully, this study used low-grade fly ash as a substitute for natural river sand in mortar. This has great potential to alleviate the [...] Read more.

Natural river sand resources are facing depletion, and large-scale mining pollutes the environment and harms humans. To utilize fly ash fully, this study used low-grade fly ash as a substitute for natural river sand in mortar. This has great potential to alleviate the shortage of natural river sand resources, reduce pollution, and improve the utilization of solid waste resources. Six types of green mortars were prepared by replacing different amounts of river sand (0, 20, 40, 60, 80, and 100%) with fly ash and other volumes. Their compressive strength, flexural strength, ultrasonic wave velocity, drying shrinkage, and high-temperature resistance were also investigated. Research has shown that fly ash can be used as a fine aggregate in the preparation of building mortar, thereby ensuring that green-building mortar has sufficient mechanical properties and better durability. The replacement rate for optimal strength and high-temperature performance was determined to be 80%. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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25 pages, 3903 KiB

Open AccessArticle

Optimization of Fly Ash—Slag One-Part Geopolymers with Improved Properties

by Iman Faridmehr, Mohammad Ali Sahraei, Moncef L. Nehdi and Kiyanets A. Valerievich

Materials 2023, 16(6), 2348; https://doi.org/10.3390/ma16062348 - 15 Mar 2023

Cited by 1 | Viewed by 1562

Abstract

One-part geopolymer concrete/mortar is a pre-mixed material made from industrial by-products and solid alkaline activators that only requires the addition of water for activation. Apart from being environmentally friendly, it also reduces complexity and improves consistency in the mixing process, leading to more [...] Read more.

One-part geopolymer concrete/mortar is a pre-mixed material made from industrial by-products and solid alkaline activators that only requires the addition of water for activation. Apart from being environmentally friendly, it also reduces complexity and improves consistency in the mixing process, leading to more efficient production and consistent material properties. However, developing one-part geopolymer concrete with desirable compressive strength is challenging because of the complexity of the chemical reaction involved, the variability of the raw materials used, and the need for precise control of curing conditions. Therefore, 80 different one-part geopolymer mixtures were compiled from the open literature in this study, and the effects of the constituent materials, the dosage of alkaline activators, curing condition, and water/binder ratio on the 28-day compressive strength of one-part geopolymer paste were examined in detail. An ANN model with the Levenberg–Marquardt algorithm was developed to estimate one-part geopolymer’s compressive strength and its sensitivity to binder constituents and alkaline dosage. The ANN model’s weights and biases were also used to develop a CPLEX-based optimization method for achieving maximum compressive strength. The results confirm that the compressive strength of one-part geopolymer pastes increased by increasing the Na₂O content of the alkaline source and the slag dosage; however, increasing the Na₂O content in alkaline sources beyond 6% by fly ash weight led to decreasing the compressive strength; therefore, the optimum alkaline activator dosage by weight of fly ash was to be 12% (i.e., 6% Na₂O). The proposed ANN model developed in this study can aid in the production and performance tuning of sustainable one-part geopolymer concrete and mortar for broader full-scale applications. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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19 pages, 6560 KiB

Open AccessArticle

Concrete Shrinkage Analysis with Quicklime, Microfibers, and SRA Admixtures

by Daumantas Židanavičius, Mindaugas Augonis, Nerijus Adamukaitis and Ignacio Villalon Fornes

Materials 2023, 16(5), 2061; https://doi.org/10.3390/ma16052061 - 02 Mar 2023

Cited by 1 | Viewed by 1188

Abstract

This research explores the effect of various humidity conditions and the efficiency of shrinkage-reducing admixtures on the free shrinkage strain of ordinary Portland cement (OPC) concrete and its mechanical properties. An OPC concrete C30/37 mixture was replenished with 5% of quicklime and 2% [...] Read more.

This research explores the effect of various humidity conditions and the efficiency of shrinkage-reducing admixtures on the free shrinkage strain of ordinary Portland cement (OPC) concrete and its mechanical properties. An OPC concrete C30/37 mixture was replenished with 5% of quicklime and 2% of organic-compound-based liquid shrinkage-reducing agent (SRA). The investigation revealed that a combination of quicklime and SRA led to the highest reduction in concrete shrinkage strain. Polypropylene microfiber addition was not so effective in reducing the concrete shrinkage as the previous two additives did. The prediction of concrete shrinkage without quicklime additive was performed according to EC2 and B4 model methods, and the obtained results were compared with the experimental ones. The B4 model evaluates the parameters more than the EC2 model does and, therefore, was modified to calculate the concrete shrinkage for the case of variable humidity and to evaluate the effect of quicklime additive. The experimental shrinkage curve that best coincides with the theoretical one was that obtained by the modified B4 model. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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15 pages, 7290 KiB

Open AccessArticle

Study on Deterioration Process of Magnesium Oxychloride Cement under the Environment of Dry–Wet Cycles

by Chenggong Chang, Lingyun An, Jinmei Dong, Weixin Zheng, Jing Wen, Fengyun Yan and Xueying Xiao

Materials 2023, 16(5), 1817; https://doi.org/10.3390/ma16051817 - 22 Feb 2023

Cited by 3 | Viewed by 1275

Abstract

To reveal the deterioration process of magnesium oxychloride cement (MOC) in an outdoor, alternating dry–wet service environment, the evolution of the macro- and micro-structures of the surface layer and inner core of MOC samples as well as their mechanical properties and increasing dry–wet [...] Read more.

To reveal the deterioration process of magnesium oxychloride cement (MOC) in an outdoor, alternating dry–wet service environment, the evolution of the macro- and micro-structures of the surface layer and inner core of MOC samples as well as their mechanical properties and increasing dry–wet cycle numbers were investigated by using a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a simultaneous thermal analyser (TG-DSC), a Fourier transform infrared spectrometer (FT-IR), and an microelectromechanical electrohydraulic servo pressure testing machine. The results show that as the number of dry–wet cycles increases, the water molecules gradually invade the interior of the samples, causing the hydrolysis of P 5 (5Mg(OH)₂·MgCl₂·8H₂O) and hydration reactions of unreacted active MgO. After three dry–wet cycles, there are obvious cracks on the surface of the MOC samples, and they suffer from warped deformation. The microscopic morphology of the MOC samples changes from a gel state and a short, rod-like shape to a flake shape, which is a relatively loose structure. Meanwhile, the main phase composition of the samples becomes Mg(OH)₂, and the Mg(OH)₂ contents of the surface layer and inner core of the MOC samples are 54% and 56%, respectively, while the P 5 amounts are 12% and 15%, respectively. The compressive strength of the samples decreases from 93.2 MPa to 8.1 MPa and reduces by 91.3%, and their flexural strength declines from 16.4 MPa to 1.2 MPa. However, their deterioration process is delayed compared with the samples that were dipped in water continuously for 21 days whose compressive strength is 6.5 MPa. This is primarily ascribed to the fact that during the natural drying process, the water in the immersed samples evaporates, the decomposition of P 5 and the hydration reaction of unreacted active MgO both slow down, and the dried Mg(OH)₂ may provide the partial mechanical properties, to some extent. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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16 pages, 5442 KiB

Open AccessArticle

The Basic Mechanical Properties and Shrinkage Properties of Recycled Micropowder UHPC

by Chengfang Yuan, Yang Chen, Dongxu Liu, Weiqian Lv and Zhe Zhang

Materials 2023, 16(4), 1570; https://doi.org/10.3390/ma16041570 - 13 Feb 2023

Cited by 5 | Viewed by 1248

Abstract

Using waste clay brick powder (RBP) to partially replace cement in the preparation of concrete, is one way to recycle construction waste. In order to investigate the physical and mechanical properties and volume stability of recycled micropowder ultra-high-performance concrete (UHPC), the basic mechanical [...] Read more.

Using waste clay brick powder (RBP) to partially replace cement in the preparation of concrete, is one way to recycle construction waste. In order to investigate the physical and mechanical properties and volume stability of recycled micropowder ultra-high-performance concrete (UHPC), the basic mechanical and shrinkage properties of recycled micropowder UHPC were studied at replacement rates of 10%, 20%, 30%, 40% and 50%. The results show that: (1) When the activated recycled brick powder is used to replace the cement, the compressive strength, flexural strength and splitting tensile strength of the UHPC initially increase and then decrease with the increase in the substitution rate. When the substitution rate is 10%, the 28 d compressive strength, flexural strength and splitting tensile strength of the UHPC are the highest; (2) Replacing cement with recycled brick powder can reduce the autogenous shrinkage of the UHPC, and the autogenous shrinkage rate of the UHPC decreases with the increase in the brick powder replacement rate. The drying shrinkage of the UHPC can be reduced by replacing cement with recycled brick powder. The drying shrinkage of the UHPC initially decreases, and then increases, with the increase in the replacement rate of brick powder. When the replacement rate of the brick powder was 30%, the drying shrinkage of the UHPC was the least, and this was 49.7% lower than that in the benchmark group. The prediction models of autogenous shrinkage and drying shrinkage are in good agreement with the experimental results, which can be used to predict the shrinkage development of recycled brick powder UHPC. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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14 pages, 4652 KiB

Open AccessArticle

Mechanical Characterization and Constitutive Modeling of Nano-Stabilized Soil under Uniaxial Compression

by Xingchen Zhang, Jianen Gao, Minmin Qiang, Haochen Zhang, Xinghua Li, Shaobo Long, Zhe Gao and Henghui Fan

Materials 2023, 16(4), 1488; https://doi.org/10.3390/ma16041488 - 10 Feb 2023

Viewed by 1159

Abstract

The stress–strain constitutive model under uniaxial compression is a basic element and important characterization method for determining physical and mechanical properties in cement-based materials research. In this study, a stress–strain constitutive model under uniaxial compression was established, which was based on a new [...] Read more.

The stress–strain constitutive model under uniaxial compression is a basic element and important characterization method for determining physical and mechanical properties in cement-based materials research. In this study, a stress–strain constitutive model under uniaxial compression was established, which was based on a new nano-stabilized soil (NSS) through typical mechanical tests and constitutive relationship research. The results indicate that the unconfined compressive strength (UCS) of the nano-stabilized soil was enhanced with the increase in curing period and nano-stabilizer dosage, and that the strength growth rate reaches the maximum at a 12% dosage in the tested samples. The UCS of NSS under a 12% dosage is about 10~15% higher than that of ordinary stabilized soil (SS) without nano doping, and 25~40% higher compared with grade 42.5 cement-soil. The established constitutive model could accurately describe the linear-elastic and elastic-plastic deformation characteristics of NSS under uniaxial compression, which will be conducive to revealing the curve variation law of the stress–strain process. The research results could provide scientific support for the theoretical innovation and engineering application of green environmental protection materials. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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20 pages, 7800 KiB

Open AccessArticle

Investigation of the Flexural Behavior of Preloaded and Pre-Cracked Reinforced Concrete Beams Strengthened with CFRP Plates

by S. M. Samindi M. K. Samarakoon, Bartosz Piatek and G. H. M. J. Subashi De Silva

Materials 2023, 16(1), 22; https://doi.org/10.3390/ma16010022 - 20 Dec 2022

Cited by 2 | Viewed by 1554

Abstract

This paper investigates the flexural behavior of preloaded reinforced concrete (RC) beams, strengthened with Carbon Fiber Reinforced Polymer (CFRP) plates using an experimental program, analytical procedure, and Finite Element Method (FEM) simulation. The RC beams were subjected to preloads of 30%, 50% and [...] Read more.

This paper investigates the flexural behavior of preloaded reinforced concrete (RC) beams, strengthened with Carbon Fiber Reinforced Polymer (CFRP) plates using an experimental program, analytical procedure, and Finite Element Method (FEM) simulation. The RC beams were subjected to preloads of 30%, 50% and 70% of the yielding load, prior to installation of the strengthening system. The eight RC-strengthened beams with a reinforcement configuration of 3Ø12 and two CarboDur S512 plates have been evaluated using bending tests. The failure modes of all the RC-strengthened beams were governed by the widening of flexural cracks within a constant bending zone, followed by debonding of the CFRP plates. The plates were debonding simultaneously or one plate prior to the other plate. The ultimate moment capacity is not significantly reduced while increasing preload levels from 0% to 70%. The moment capacity is increased by 70% to 80% in the CFRP strengthened beams, compared with un-strengthened beams indicating the potential of capacity enhancement that can be attained by externally bonded CFRP. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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17 pages, 2845 KiB

Open AccessArticle

Nonlinear Creep Amplification Factor Considering Damage Evolution of Concrete under Compression

by Zuanfeng Pan, Dong Cao, Bin Zeng and Yuwei Wang

Materials 2022, 15(19), 6742; https://doi.org/10.3390/ma15196742 - 28 Sep 2022

Cited by 1 | Viewed by 1362

Abstract

Creep affects the long-term deformation of concrete structures. Nonlinear creep further overestimates the safety factor of structures and affects the safety service performance. The coupling of creep and a damage model considering the rate effect is conducive to accurate prediction of nonlinear creep, [...] Read more.

Creep affects the long-term deformation of concrete structures. Nonlinear creep further overestimates the safety factor of structures and affects the safety service performance. The coupling of creep and a damage model considering the rate effect is conducive to accurate prediction of nonlinear creep, but the iterative process of strain makes the calculation method more complex. The purpose of this study is to propose a nonlinear creep explicit method that considers the damage evolution of concrete under compression. Two groups of axial compression members with compressive stresses of 0.2 fc and 0.4 fc were made. Considering the law of concrete damage evolution under uniaxial compression, coupled with elastic creep and damage incremental strain, the lower limit of the medium stress level that gives rise to nonlinear creep is analyzed. The concrete nonlinear creep amplification coefficient with a loading age of 28 days and loading duration of 360 days is studied with consideration for the uncertainty of relative humidity and the theoretical thickness of the component. On this basis, the explicit calculation formula of the nonlinear creep amplification coefficient related to the concrete axial compressive strength and stress level is given. The results indicate that the nonlinear creep amplification coefficient increases nonlinearly with an increase in the stress level, and, when the compressive stress level ratio is higher than 0.6, the nonlinear creep amplification coefficient increases significantly; when the stress level is determined, the creep amplification coefficient decreases gradually with an increase in the compressive strength of the concrete. It is suggested that a stress level range of 0.35~0.75 should be used for the study of a nonlinear creep amplification factor under the medium stress state. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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17 pages, 12950 KiB

Open AccessArticle

Experimental Investigation of Cohesion between UHPC and NSC Utilising Interface Protrusions

by Pavel Horák, Šárka Pešková, Marcel Jogl, Radoslav Sovják and Petr Vítek

Materials 2022, 15(19), 6537; https://doi.org/10.3390/ma15196537 - 21 Sep 2022

Cited by 3 | Viewed by 1227

Abstract

The interaction of ultrahigh-performance concrete (UHPC) and normal-strength concrete (NSC) is one of the main issues for strengthening conventional concrete structures or other applications where NSC and UHPC are interrelated. UHPC stands out for its strength and durability, while NSC is significantly inexpensive [...] Read more.

The interaction of ultrahigh-performance concrete (UHPC) and normal-strength concrete (NSC) is one of the main issues for strengthening conventional concrete structures or other applications where NSC and UHPC are interrelated. UHPC stands out for its strength and durability, while NSC is significantly inexpensive and easier to work with. Efficiently designed structures can exploit the advantages of both mixtures. At the interface of these materials in newly designed structures, the formwork can be modified at the interface to give the concrete surface sufficient roughness and thus cohesion as required. This improves both the tensile and shear strength of the contact resulting in the enhanced capacity of the composite structure. In this study, a button foil was inserted into the formwork for the UHPC and then a part of NSC was made. The shear strength of the interface without any stress component in the transverse direction was measured on small-scale samples. It was to justify the possibility of the use of this interface in real constructions such as beams and columns. The main objective of further research is to design a composite beam using a UHPC shell as formwork for NSC and protrusions at the interface. It is expected that the U-shaped shell made of the UHPC could significantly contribute to the load-bearing capacity of the resulting composite NSC–UHPC structure and also to its enhanced durability. In addition, if the NSC is enclosed in a shell of UHPC, it can be made from various secondary materials, therefore it can decrease cement consumption by more than 50%. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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15 pages, 4483 KiB

Open AccessArticle

Research on the Properties and Mechanism of Carbon Nanotubes Reinforced Low-Carbon Ecological Cement-Based Materials

by Kai Cui, Jixin Zhang, Jun Chang, Mohanad Muayad Sabri Sabri and Jiandong Huang

Materials 2022, 15(18), 6435; https://doi.org/10.3390/ma15186435 - 16 Sep 2022

Cited by 1 | Viewed by 1214

Abstract

SAC (sulfoaluminate cement) has become a research hotspot as a low-carbon ecological cement. In addition, multi-walled carbon nanotubes have good thermal, mechanical, and electrical properties and can serve as excellent nano-reinforced cement-based fillers. This study explored the dispersion of carbon nanotubes (CNTs) and [...] Read more.

SAC (sulfoaluminate cement) has become a research hotspot as a low-carbon ecological cement. In addition, multi-walled carbon nanotubes have good thermal, mechanical, and electrical properties and can serve as excellent nano-reinforced cement-based fillers. This study explored the dispersion of carbon nanotubes (CNTs) and researched the effect of CNTs on the mechanical properties, hydration process, hydration products, and microstructure of SAC paste, and the mechanism of CNT-enhanced SAC paste was revealed. The results showed that the mechanical properties of SAC paste were significantly improved after the addition of CNTs. When the CNT content was 0.05%, 0.1%, and 0.15%, the compressive strength after 28 d was increased by 13.2%, 18.3%, and 22.5%, respectively; compared with the C0 group (without CNTs), the flexural strength increased by 8.2%, 11.3%, and 14.4%, respectively. The addition of CNTs accelerated the hydration process of SAC paste. Due to the adsorption effect and nucleation effect of CNTs, more hydration products were generated, filling the matrix’s pores and improving its compactness. The mechanism of CNTs enhanced SAC paste was revealed. CNTs and hydration products co-filled the pores, including AFt (ettringite) and AH₃ (gibbsite). CNTs improve the mechanical properties of SAC paste through filling, bridging, crack bending, deflection, pulling out, and pulling off. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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13 pages, 2987 KiB

Open AccessArticle

Experimental Study and Analysis on Workability and Mechanical Performance of High Fluidity Recycled Concrete

by Cun Hui, Yan Liu, Ran Hai and Mingliang Liu

Materials 2022, 15(17), 6104; https://doi.org/10.3390/ma15176104 - 02 Sep 2022

Cited by 3 | Viewed by 1068

Abstract

In order to study the workability and mechanical performance of high fluidity recycled concrete, parallel tests were carried out to prepare high fluidity recycled concrete by changing the amount of recycled aggregate (20%, 30%, 40%, 50% and 60%) and the sand ratio (0.37, [...] Read more.

In order to study the workability and mechanical performance of high fluidity recycled concrete, parallel tests were carried out to prepare high fluidity recycled concrete by changing the amount of recycled aggregate (20%, 30%, 40%, 50% and 60%) and the sand ratio (0.37, 0.38, 0.39 and 0.40). The fluidity, compression strength, tensile strength and flexural strength of each mix were tested. The results show that the slump of a recycled concrete mixture is 120 mm when the content of recycled aggregate is less than 30%, and the mechanical strength satisfies the requirement of the high fluidity ordinary concrete. As the ratio of sand increases, the fluidity of the recycled concrete also improved. The best sand ratio is not consistent with the strength index. When the sand ratio is between 0.37 and 0.40 and the content of recycled aggregate is not more than 40%, the concrete of C60 can be prepared. Both the fluidity and the strength index can meet the design requirements and can be used in the practical engineering. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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18 pages, 5162 KiB

Open AccessArticle

Influence of Magnetic Water on Concrete Properties with Different Magnetic Field Exposure Times

by Malathy Ramalingam, Karuppasamy Narayanan, Arivoli Masilamani, Parthiban Kathirvel, Gunasekaran Murali and Nikolai Ivanovich Vatin

Materials 2022, 15(12), 4291; https://doi.org/10.3390/ma15124291 - 17 Jun 2022

Cited by 10 | Viewed by 2018

Abstract

The characteristics of a concrete mix are purely dependent on the hydration of cement that is carried forward by using the water quality used in the mix. Several researchers have focused on incorporating pozzolanic or nanomaterials to improve the hydration mechanisms and impart [...] Read more.

The characteristics of a concrete mix are purely dependent on the hydration of cement that is carried forward by using the water quality used in the mix. Several researchers have focused on incorporating pozzolanic or nanomaterials to improve the hydration mechanisms and impart high strength to concrete. A new technology has been introduced to improve the properties of concrete by magnetic-field-treated water (MFTW). Due to magnetization, water particles become charged and the molecules inside the water cluster decrease from 13 to 5 or 6, which eventually decreases the hardness of water, thus improving the strength of concrete when compared to the use of normal water (NW). In advanced construction techniques and practices, the application of Magnetic Water (MW) plays an important role in boosting physicochemical properties. This research work focused on evaluating the standards of water quality through physiochemical analysis, such as Electrical Conductivity (EC), Viscosity, pH, and Total Dissolved Solids (TDS) with the MW at different exposure periods (60 min (MW60), 45 min (MW45), 30 min (MW30), 15 min (MW15), and instant exposure (MWI)). Experiments were carried out to evaluate the fresh, hardened, and microstructural behavior of concrete made with magnetic water (MW) using a permanent magnet of PERMAG (N407) under a field intensity of 0.9 Tesla. In addition, optical properties such as X-ray Diffraction (XRD) and Ultraviolet (UV) absorption were considered for the MW60 mix to ensure water magnetization. Characterization methods such as Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM) were employed for NWC and MWC to quantify the hydrated products. From the results, it was observed that the magnetic effect on water characteristics showed significant improvement in the concrete properties with the increase in exposure duration. There were increments of 25.6% and 24.1% in workability and compressive strength, respectively, for the MW60 mix compared to normal water concrete (NWC). Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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13 pages, 45944 KiB

Open AccessArticle

Reactive Powder Concrete Microstructure and Particle Packing

by Evgeny Georgievich Velichko and Nikolai Ivanovich Vatin

Materials 2022, 15(6), 2220; https://doi.org/10.3390/ma15062220 - 17 Mar 2022

Cited by 1 | Viewed by 1340

Abstract

The subject of this study is the dispersed composition of multicomponent cement systems. This study aims to reduce interparticle voids, increasing the strength and concentration of the solid phase. The investigated concrete mixture contained two fine aggregate fractions, granite-gabbro crushed stone of 5–10 [...] Read more.

The subject of this study is the dispersed composition of multicomponent cement systems. This study aims to reduce interparticle voids, increasing the strength and concentration of the solid phase. The investigated concrete mixture contained two fine aggregate fractions, granite-gabbro crushed stone of 5–10 mm fraction, Portland cement of CEM I 42.5N class, finely dispersed granular blast furnace slag, microsilica, highly dispersed cement fraction, superplasticizer Glenium 430, and high-valence hardening accelerator. A laser analyzer determined the shape and size of dispersed particles of the components. The structure of the cement stone was studied by scanning microscopy, thermographic, and X-ray phase analysis methods. The strength of concrete with an optimized dispersed composition at the age of 2 days was 52, 63, and 74 MPa, while that at the age of 28 days was 128, 137, and 163 MPa. For this concrete, the consumption of multicomponent cement was 650, 700, and 750 kg/m³, respectively. The high efficiency of the application of bimodal clinker component and granulated blast-furnace slag is shown. It is established that the optimal content of nanoscale additives, including microsilica, should be insignificant and determined experimentally. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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15 pages, 15918 KiB

Open AccessArticle

Effect of Ca(OH)₂ Addition on the Engineering Properties of Sodium Sulfate Activated Slag

by Xiaodi Dai, Serdar Aydın, Mert Yücel Yardımcı, Karel Lesage and Geert De Schutter

Materials 2021, 14(15), 4266; https://doi.org/10.3390/ma14154266 - 30 Jul 2021

Cited by 22 | Viewed by 2805

Abstract

Alkali-activated slag is considered as a sustainable construction material due to its environmentally friendly nature. To further promote the sustainable nature of alkali-activated slag, a sodium sulfate activator is suggested to be used since it can be obtained naturally and generates lower greenhouse [...] Read more.

Alkali-activated slag is considered as a sustainable construction material due to its environmentally friendly nature. To further promote the sustainable nature of alkali-activated slag, a sodium sulfate activator is suggested to be used since it can be obtained naturally and generates lower greenhouse gas emissions. However, the mixtures activated by sodium sulfate exhibit low early strength and very long setting times. This study investigates the effects of calcium hydroxide (Ca(OH)₂) addition on some engineering properties such as rheology, setting time, mechanical properties, porosity, and microstructure of sodium sulfate activated ground granulated blast furnace slag (GGBFS). Furthermore, the changes of chemical groups in reaction products and phase identification have been evaluated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. Test results showed that Ca(OH)₂ addition can substantially increase the reaction rate and the compressive strength at early ages. In addition, the very long setting times of the sodium sulfate-activated mixtures were shortened by the addition of Ca(OH)₂. SEM analysis confirmed that the incorporation of excessive amounts of Ca(OH)₂ could lead to a less well-packed microstructure although the reaction degree of GGBFS remained the same at later ages as compared to the sodium sulfate mixture. It was also revealed that in case of the Ca(OH)₂ addition into sodium sulfate activator, the main reaction products are chain-structured C-A-S-H gels and ettringite. Full article

(This article belongs to the Special Issue Advances in the Mechanical Properties of Cements, Mortars and Concretes)

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