Research

13 pages, 4787 KiB

Open AccessArticle

Physical Properties and Hydration Characteristics of Low-Heat Portland Cement at High-Altitude

by Ning Wang, Qiang Liu, Yanqing Xia, Jun Li, Zhongyuan Lu, Yigang Xu, Wen Zhong and Yan Lin

Materials 2023, 16(8), 3110; https://doi.org/10.3390/ma16083110 - 14 Apr 2023

Cited by 1 | Viewed by 1107

Abstract

High-altitude environments are characterized by low air pressures and temperature variations. Low-heat Portland cement (PLH) is a more energy-efficient alternative to ordinary Portland cement (OPC); however, the hydration properties of PLH at high altitudes have not been previously investigated. Therefore, in this study, [...] Read more.

High-altitude environments are characterized by low air pressures and temperature variations. Low-heat Portland cement (PLH) is a more energy-efficient alternative to ordinary Portland cement (OPC); however, the hydration properties of PLH at high altitudes have not been previously investigated. Therefore, in this study, the mechanical strengths and levels of the drying shrinkage of PLH mortars under standard, low-air-pressure (LP), and low-air-pressure and variable-temperature (LPT) conditions were evaluated and compared. In addition, the hydration characteristics, pore size distributions, and C-S-H Ca/Si ratio of the PLH pastes under different curing conditions were explored using X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). Compared with that of the PLH mortar cured under the standard conditions, the compressive strength of the PLH mortar cured under the LPT conditions was higher at an early curing stage but lower at a later curing stage. In addition, drying shrinkage under the LPT conditions developed rapidly at an early stage but slowly at a later stage. Moreover, the characteristic peaks of ettringite (AFt) were not observed in the XRD pattern after curing for 28 d, and AFt transformed into AFm under the LPT conditions. The pore size distribution characteristics of the specimens cured under the LPT conditions deteriorated, which was related to water evaporation and micro-crack formation at low air pressures. The low pressure hindered the reaction between belite and water, which contributed to a significant change in the C-S-H Ca/Si ratio in the early curing stage in the LPT environment. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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19 pages, 7819 KiB

Open AccessArticle

Modelling the Influence of Composition on the Properties of Lightweight Plaster Mortar and Multicriteria Optimisation

by Khrystyna Moskalova, Tatiana Lyashenko, Aleksej Aniskin and Matija Orešković

Materials 2023, 16(7), 2846; https://doi.org/10.3390/ma16072846 - 03 Apr 2023

Viewed by 1472

Abstract

The influence of the components of plaster mortars on their properties is considered in a lot of studies at a qualitative level without searching for optimal compositions of these multicomponent composite materials. The purpose of this study was to obtain the experimental–statistical models [...] Read more.

The influence of the components of plaster mortars on their properties is considered in a lot of studies at a qualitative level without searching for optimal compositions of these multicomponent composite materials. The purpose of this study was to obtain the experimental–statistical models based on the results of the designed experiment, allowing the influence of light fillers and polymer admixtures on the properties of the mortars to be evaluated and analysed; the compositions complying with specified requirements and compromised optimally by a number of properties should be found. The quantities of fine limestone and perlite as well as of the hydroxyethyl methyl cellulose and dispersible polymer were varied in the experiment. The effective viscosity and thixotropy of the mix, compression, tensile, adhesive strength, frost resistance, and density of hardened mortars were determined for 18 compositions according to the experiment design. The obtained models have allowed the individual and synergetic effects of mix components to be evaluated. The fine perlite has turned out to have the greatest positive effect on the properties. This porous filler increases the strength while decreasing the density of the mortars. It is shown how the composition complying with specified requirements—and the best based on several properties—has been found. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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22 pages, 3627 KiB

Open AccessArticle

New Approach to Determine the Activity Concentration Index in Cements, Fly Ashes, and Slags on the Basis of Their Chemical Composition

by Andrés Caño, José Antonio Suárez-Navarro, Francisca Puertas, Ana Fernández-Jiménez and María del Mar Alonso

Materials 2023, 16(7), 2677; https://doi.org/10.3390/ma16072677 - 28 Mar 2023

Cited by 2 | Viewed by 1324

Abstract

The manufacture of Portland cement entails high energy and environmental costs, and various solutions have been implemented in recent years to mitigate this negative impact. These solutions include improvements in the manufacture of cement clinker or the use of supplementary cementitious materials (SCMs), [...] Read more.

The manufacture of Portland cement entails high energy and environmental costs, and various solutions have been implemented in recent years to mitigate this negative impact. These solutions include improvements in the manufacture of cement clinker or the use of supplementary cementitious materials (SCMs), such as fly ash (FA) or slag as a replacement for a portion of the clinker in cement. The incorporation of these SCMs in cement may increase its radiological content as they are naturally occurring radioactive materials (NORMs). The Activity Concentration Index (ACI) is a screening tool established in the European EURATOM Directive 2013/59 to determine the radiation protection suitability of a final construction material. The ACI is determined by the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K, usually determined by gamma spectrometry. The methodology of gamma spectrometry is accurate and appropriate, but this technique is not available in all laboratories. For this reason, and taking into account that there is a relationship between the chemical and radiological composition of these building materials, a new approach is proposed to determine the radiological content of these materials from a chemical analysis such as X-ray fluorescence (XRF). In this paper, principal component analysis (PCA) is used to establish the relationships between the chemical composition and radiological content of cements, FAs, and slags of different natures. Through PCA it was possible to group the cements based on two variables: CaO content and Fe₂O_3–Al₂O_3–TiO₂ content. A lower correlation was observed for the FAs and slags, as the sample scores were centered around the origin of the coordinates and showed greater dispersion than the cements. The clusters obtained in the HJ–Biplots allowed the determination, using multiple regression, of models relating the activity concentration of ²²⁶Ra, ²³²Th (²¹²Pb), and ⁴⁰K to the oxide percentages obtained for the three matrices studied. The models were validated using five cements, one FA and one slag with relative percentage deviations (RSD(%)) equal to or less than 30% for 89% of the activity concentrations and 100% of the ACI determined. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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11 pages, 1383 KiB

Open AccessArticle

Effects on the Properties of Self-Compacting Cement Paste (PAA) with the Addition of Superabsorbent Polymer

by Michel Henry Bacelar de Souza, Bárbara Almeida Teixeira, Paulo Cesar Gonçalves, Lucas Ramon Roque da Silva, Míriam de Lourdes Noronha Motta Melo, Vander Alkmin dos Santos Ribeiro, Daniela Sachs, Patrícia Capellato and Valquíria Claret dos Santos

Materials 2022, 15(23), 8478; https://doi.org/10.3390/ma15238478 - 28 Nov 2022

Cited by 1 | Viewed by 1018

Abstract

The addition of Superabsorbent Polymer (SAP) decreases the effect of autogenous shrinkage present in pastes, mortars, and concretes. In this study we investigated the influence of the addition of SAP in self-compacting cement paste mixtures. Eighteen 5 × 10 cylindrical specimens were molded [...] Read more.

The addition of Superabsorbent Polymer (SAP) decreases the effect of autogenous shrinkage present in pastes, mortars, and concretes. In this study we investigated the influence of the addition of SAP in self-compacting cement paste mixtures. Eighteen 5 × 10 cylindrical specimens were molded in all, three for each mixture (CPII base, CPII 0.15%SAP/600μm, CPII 0.15%SAP/800 μm, CPV base, CPV 0.15%SAP/600 μm, CPV 0.15%SAP/800 μm). Two types of cement were tested, CP II-Z and CP V-ARI with 0.15% of weight replaced per two diameters of SAP (600 μm and 800 μm). The samples followed the standards required. Mini slump tests were carried out in the fresh state, and uniaxial compressive strength, elastic modulus, specific mass, absorption, and air content in the hardened state after 28 days. The results obtained show the SAP is high indicated to replaced cement in small % of weight i/to fresh and hardened paste. Likewise, the group mix n° 3 composed of CPII 0.15% of SAP with 800 μm diameter presented the best result. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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16 pages, 5909 KiB

Open AccessArticle

Prediction of the Rheological Properties of Fresh Cementitious Suspensions Considering Microstructural Parameters

by Sam Rajadurai Rajagopalan, Bang-Yeon Lee and Su-Tae Kang

Materials 2022, 15(20), 7044; https://doi.org/10.3390/ma15207044 - 11 Oct 2022

Cited by 3 | Viewed by 1278

Abstract

Supplementary cementitious materials (SCMs) are commonly used to partially replace cements. Although it is necessary to investigate the rheological properties of the individual supplementary cementitious materials (SCMs) for understanding complex rheological behaviors of the blended mixes, the study on the investigation of rheological [...] Read more.

Supplementary cementitious materials (SCMs) are commonly used to partially replace cements. Although it is necessary to investigate the rheological properties of the individual supplementary cementitious materials (SCMs) for understanding complex rheological behaviors of the blended mixes, the study on the investigation of rheological properties of various SCMs such as fly ash, blast-furnace slag, and silica fume, according to various solid volume fractions and prediction models is fairly limited. This study investigated the rheological properties of non-blended cementitious suspensions with Portland cement (PC), fly ash (FA), blast-furnace slag (BS), and silica fume (SF) materials in the experiments and predicted using YODEL (Yield stress mODEL) and Krieger–Dougherty’s (K–D’s) equation. Experiments were designed with various solid volume fractions (

ϕ

) from 0.28 to 0.44, and the rheological properties of all cementitious suspensions were noted to increase with increasing

ϕ

, showing an improved flowability at low

ϕ

. YODEL, derived from the first principles considering particle-size distributions, interparticle forces and microstructural parameters predicted the yield stress. The YODEL predictions were consistent with the experiments with a positive correlation coefficient of above 0.96. K–D’s equation with the maximum particle fractions and intrinsic viscosity as key parameters predicted the plastic viscosity. The K–D’s equation predictions match up with the experiments with a positive correlation coefficient of above 0.94. Both models showed more quantitative predictions without any fitting parameters and could be applied to any multimodal powder suspensions. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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12 pages, 17105 KiB

Open AccessArticle

Study on an Epoxy Resin System Used to Improve the Elasticity of Oil-Well Cement-Based Composites

by Jianjian Song, Mingbiao Xu, Chunqin Tan, Fuchang You, Xiaoliang Wang and Shanshan Zhou

Materials 2022, 15(15), 5258; https://doi.org/10.3390/ma15155258 - 29 Jul 2022

Cited by 10 | Viewed by 1423

Abstract

Oil-well cement-based materials have inherent brittleness; therefore, they cannot be directly used to seal oil and gas wells for a long time. To improve the elasticity of oil-well cement-based composites, a flexible epoxy resin system was developed. The flexibility, TG, and SEM of [...] Read more.

Oil-well cement-based materials have inherent brittleness; therefore, they cannot be directly used to seal oil and gas wells for a long time. To improve the elasticity of oil-well cement-based composites, a flexible epoxy resin system was developed. The flexibility, TG, and SEM of the cured resin system were evaluated. At the same time, the resin was added to oil-well cement-based materials to improve its elasticity. The compressive strength and elastic modulus of resin cement stone were tested, and the microstructure was analyzed by XRD, TG, and SEM/EDS. The results showed that the structure of the cured resin is compact, the thermal decomposition temperature is 243.9 °C, and it can recover its original shape after compression. At the curing age of 28 days, the compressive strength of cement-based composites containing 30% resin decreased by 26.7%, while the elastic modulus significantly decreased by 63.2%, and the elasticity of cement-based composites was significantly improved. The formation of hydration products (e.g., calcium silicate hydrate, and calcium hydroxide) in the resin cement slurry is obviously lower than that of pure cement, which is the reason for the decrease in compressive strength. The flexible structure of polymer particles and polymer film formed by epoxy resin is distributed inside the cement stone, which significantly improves the elasticity of oil-well cement-based composites. The results of this paper are helpful for the design of elastic cement slurry systems. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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29 pages, 9667 KiB

Open AccessArticle

Frost Resistance Investigation of Fiber-Doped Cementitious Composites

by Yongcheng Ji, Yunfei Zou, Yulong Ma, Haoxiang Wang, Wei Li and Wenyuan Xu

Materials 2022, 15(6), 2226; https://doi.org/10.3390/ma15062226 - 17 Mar 2022

Cited by 9 | Viewed by 1637

Abstract

Fibers used as reinforcement can increase the mechanical characteristics of engineering cementitious composites (ECC), but their frost resistance has received less attention. The mechanical properties of various fiber cementitious materials under the dual factors of freeze-thaw action and fiber dose are yet to [...] Read more.

Fibers used as reinforcement can increase the mechanical characteristics of engineering cementitious composites (ECC), but their frost resistance has received less attention. The mechanical properties of various fiber cementitious materials under the dual factors of freeze-thaw action and fiber dose are yet to be determined. This study examines the performance change patterns of cementitious composites, which contain carbon fiber, glass fiber, and polyvinyl alcohol (PVA) fiber at 0%, 0.5%, and 1% volume admixture in freeze-thaw tests. Three fiber cement-based materials are selected to do the compression and bending testing, and ABAQUS finite element modeling is used to assess the performance of fiber cement-based composite materials. The microscopic observation results show that the dispersion of glass and PVA fibers is higher than that of carbon fibers. As a result, the mechanical characteristics of the fiber-doped cementitious composites increase dramatically after freeze-thaw with increasing dosage. The compression test results show the frost resistance of carbon fiber > PVA fiber > glass fiber. In addition, the bending test results show the frost resistance of carbon fiber > glass fiber > PVA fiber. The 3D surface plots of the strength changes are established to observe the mechanical property changes under the coupling effect of admixture and freeze-thaw times. ABAQUS modeling is used to predict the strength of the cementitious composites under various admixtures and freeze-thaw cycles. The bending strength numerical equation is presented, and the bending and compressive strengths of three different fiber-cement matrix materials are accurately predicted. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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21 pages, 7470 KiB

Open AccessFeature PaperArticle

Rheological Behavior of High-Performance Shotcrete Mixtures Containing Colloidal Silica and Silica Fume Using the Bingham Model

by Kyong Ku Yun, Jong Beom Kim, Chang Seok Song, Mohammad Shakhawat Hossain and Seungyeon Han

Materials 2022, 15(2), 428; https://doi.org/10.3390/ma15020428 - 06 Jan 2022

Cited by 9 | Viewed by 1674

Abstract

There have been numerous studies on shotcrete based on strength and durability. However, few studies have been conducted on rheological characteristics, which are very important parameters for evaluating the pumpability and shootability of shotcrete. In those studies, silica fume has been generally used [...] Read more.

There have been numerous studies on shotcrete based on strength and durability. However, few studies have been conducted on rheological characteristics, which are very important parameters for evaluating the pumpability and shootability of shotcrete. In those studies, silica fume has been generally used as a mineral admixture to simultaneously enhance the strength, durability, pumpability, and shootability of shotcrete. Silica fume is well-known to significantly increase the viscosity of a mixture and to prevent material sliding at the receiving surface when used in shotcrete mixtures. However, the use of silica fume in shotcrete increases the possibility of plastic shrinkage cracking owing to its very high fineness, and further, silica fume increases the cost of manufacturing the shotcrete mixture because of its cost and handling. Colloidal silica is a new material in which nano-silica is dispersed in water, and it could solve the above-mentioned problems. The purpose of this research is to develop high-performance shotcrete with appropriate levels of strength and workability as well as use colloidal silica for normal structures without a tunnel structure. Thereafter, the workability of shotcrete with colloidal silica (2, 3, and 4%) was evaluated with a particle size of 10 nm and silica fume replacement (4 and 7%) of cement. In this study, an air-entraining agent for producing high-performance shotcrete was also used. The rheological properties of fresh shotcrete mixtures were estimated using an ICAR rheometer and the measured rheological parameters such as flow resistance and torque viscosity were correlated with the workability and shootability. More appropriate results will be focusing on the Bingham model properties such that the main focus here is to compare all data using the Bingham model and its performance. The pumpability, shootability, and build-up thickness characteristics were also evaluated for the performance of the shotcrete. This research mainly focuses on the Bingham model for absolute value because it creates an exact linear line in a graphical analysis, which provides more appropriate results for measuring the shotcrete performance rather than ICAR rheometer relative data. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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15 pages, 2400 KiB

Open AccessArticle

Modelling the Relations of Rheological Characteristics with Composition of Plaster Mortar

by Khrystyna Moskalova, Tatiana Lyashenko and Aleksej Aniskin

Materials 2022, 15(1), 371; https://doi.org/10.3390/ma15010371 - 05 Jan 2022

Cited by 5 | Viewed by 1704

Abstract

The rheological properties of fresh plaster mortars, with varied contents of porous fillers and polymer admixtures, have been studied. The quantities of fine limestone and expanded perlite, and dosages of methyl hydroxy ethyl cellulose and ethylene vinyl acetate were varied in the experiment. [...] Read more.

The rheological properties of fresh plaster mortars, with varied contents of porous fillers and polymer admixtures, have been studied. The quantities of fine limestone and expanded perlite, and dosages of methyl hydroxy ethyl cellulose and ethylene vinyl acetate were varied in the experiment. Effective viscosity (at a shear rate from 0.045 to 5.705 s⁻¹) and the thixotropy of the mixes were determined with rotational viscometer for 18 compositions (according to the design of the experiment). Each of the 18 viscosity curves were described with the Ostwald–de-Waele equation. The Experimental–Statistical models describing the dependencies of the parameters of the rheological model and of mix thixotropy on the composition factors were built on the obtained data. ES-models have allowed the individual and synergetic effects of mix components on the rheological characteristics to be evaluated. The expanded perlite powder can increase the viscosity by two times, probably due to its pozzolanic effect increasing the content of the CSH phase during cement hydration. The thixotropy can be increased by the quantity of limestone. The computational experiments with ES-models have made it possible for the information set, without a noticeable interrelation between rheological characteristics, to be stratified into subsets, in which such interrelations differ significantly. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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18 pages, 15979 KiB

Open AccessArticle

In Situ Remediation of Phosphogypsum with Water-Washing Pre-Treatment Using Cemented Paste Backfill: Rheology Behavior and Damage Evolution

by Yikai Liu, Qiusong Chen, Yunmin Wang, Qinli Zhang, Hongpeng Li, Chaoyu Jiang and Chongchong Qi

Materials 2021, 14(22), 6993; https://doi.org/10.3390/ma14226993 - 18 Nov 2021

Cited by 7 | Viewed by 1701

Abstract

The accumulation of original phosphogypsum (OPG) has occupied considerable land resources, which have induced significant environmental problems worldwide. The OPG-based cemented paste backfill (OCPB) has been introduced as a promising solution. In this study, a water-washing pre-treatment was used to purify OPG, aiming [...] Read more.

The accumulation of original phosphogypsum (OPG) has occupied considerable land resources, which have induced significant environmental problems worldwide. The OPG-based cemented paste backfill (OCPB) has been introduced as a promising solution. In this study, a water-washing pre-treatment was used to purify OPG, aiming to optimize the transport performance and mechanical properties of backfills. The overall results proved that in treated phosphogypsum-based cemented paste backfill (TCPB), the altered particle size distribution can alleviate the shear-thinning characteristic. The mechanical properties were significantly optimized, of which a maximum increase of 183% of stress value was observed. With more pronounced AE signals, the TCPB samples demonstrated better residual structures after the ultimate strength values but with more unstable cracks with high amplitude generated during loading. Principal component analysis confirmed the adverse effects of fluorine and phosphorus on the damage fractal dimensions. The most voluminous hydration products observed were amorphous CSH and ettringite. The interlocked stellate clusters may be associated with the residual structure and the after-peak AE events evident in TCPB, indicate that more significant stress should be applied to break the closely interlocked stitches. Ultimately, the essential findings in this experimental work can provide a scientific reference for efficient OPG recycling. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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27 pages, 12917 KiB

Open AccessEditor’s ChoiceArticle

Durability Investigation of Carbon Fiber Reinforced Concrete under Salt-Freeze Coupling Effect

by Yongcheng Ji, Wenchao Liu, Yanmin Jia and Wei Li

Materials 2021, 14(22), 6856; https://doi.org/10.3390/ma14226856 - 13 Nov 2021

Cited by 3 | Viewed by 1687

Abstract

In order to study the durability behavior of CFRP (carbon fiber reinforced polymer) reinforced concrete, three category specimens (plain, partially reinforced, and fully reinforced) were selected to investigate its performance variation concerning chlorine salt and salt-freeze coupled environment, which included the microscopic examination, [...] Read more.

In order to study the durability behavior of CFRP (carbon fiber reinforced polymer) reinforced concrete, three category specimens (plain, partially reinforced, and fully reinforced) were selected to investigate its performance variation concerning chlorine salt and salt-freeze coupled environment, which included the microscopic examination, the distribution of chloride ion concentration, and the compressive properties. By observing the microscopic of the specimens, the surface and cross-section corrosion deterioration was examined with increasing exposure time, and the physical behavior of CFRP and core concrete were discussed. The chloride ion diffusion test exerted that the chloride ion concentration in plain specimens is at least 200 times higher than that of fully reinforced specimens. Therefore, the effectiveness of CFRP reinforcement will be proved to effectively hinder the penetration of chloride ions into the core section. The formula of the time-dependent effect of concrete diffusivity with salt-freeze coupling effect was presented and its accuracy verified. A time-varying finite element model of chloride ion distribution was established by using ABAQUS software. It can be seen from the axial compression test that the strength loss rate of three categories of specimens was varied when subjected to the corrosion environment. Therefore, it is proved that CFRP reinforcement can effectively reduce the deterioration of the specimen’s mechanical properties caused by the exposure environment. The research results can provide technical reference for applying the CFRP strengthened concrete in a severe salt-freeze environment. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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16 pages, 5190 KiB

Open AccessArticle

Study of the Properties of Blended Cements Containing Various Types of Slag Cements and Limestone Powder

by Małgorzata Gołaszewska and Zbigniew Giergiczny

Materials 2021, 14(20), 6072; https://doi.org/10.3390/ma14206072 - 14 Oct 2021

Cited by 4 | Viewed by 1549

Abstract

It is currently vital to use more environmentally friendly cementitious composites, such as blended slag-limestone cements. However, many properties of slag-limestone cements are not yet fully research, especially in regards to the effect of limestone properties on properties of mortars and concrete. In [...] Read more.

It is currently vital to use more environmentally friendly cementitious composites, such as blended slag-limestone cements. However, many properties of slag-limestone cements are not yet fully research, especially in regards to the effect of limestone properties on properties of mortars and concrete. In the research, three types of slag cements were mixed with two types of limestone to obtain multi-component slag-limestone cements. Tests of rheological properties, heat of hydration, and compressive strength were conducted to ascertain the effect of limestone on the cement properties and to check the viability of this type of cement for engineering practice. It was found that the addition of up to 10% of limestone to slag cements did not have negative effects on tested properties; however, the exact influence of limestone was dependent on limestone particle size distribution. Increasing the amount of limestone in limestone-slag cements to 15% significantly decreased the compressive strength of the mortars and decreased hydration heat but had no significant effect on rheological properties. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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19 pages, 4202 KiB

Open AccessEditor’s ChoiceArticle

Effect of Boron and Water-to-Cement Ratio on the Performances of Laboratory Prepared Belite-Ye’elimite-Ferrite (BYF) Cements

by Raquel Pérez-Bravo, Alejandro Morales-Cantero, Margherita Bruscolini, Miguel A. G. Aranda, Isabel Santacruz and Angeles G. De la Torre

Materials 2021, 14(17), 4862; https://doi.org/10.3390/ma14174862 - 26 Aug 2021

Cited by 8 | Viewed by 1643

Abstract

The effect of superplasticiser, borax and the water-to-cement ratio on BYF hydration and mechanical strengths has been studied. Two laboratory-scale BYF cements—st-BYF (with β-C₂S and orthorhombic C₄A₃

\bar{S}

) and borax-activated B-BYF (with α’_H-C₂ [...] Read more.

The effect of superplasticiser, borax and the water-to-cement ratio on BYF hydration and mechanical strengths has been studied. Two laboratory-scale BYF cements—st-BYF (with β-C₂S and orthorhombic C₄A₃

\bar{S}

) and borax-activated B-BYF (with α’_H-C₂S and pseudo-cubic C₄A₃

\bar{S}

)—have been used, and both show similar particle size distribution. The addition of superplasticiser and externally added borax to BYF pastes has been optimised through rheological measurements. Optimised superplasticiser contents (0.3, 0.4 and 0.1 wt % for st-BYF, B-BYF and st-BYF with externally added 0.25 wt % B₂O₃, respectively) result in low viscosities yielding homogeneous mortars. The calorimetric study revealed that st-BYF is more reactive than B-BYF, as the values of heat released are 300–370 J/g and 190–210 J/g, respectively, after 7 days of hydration; this fact is independent of the water-to-cement ratio. These findings agree with the higher degree of hydration at 28 days of β-C₂S in st-BYF (from 45 to 60%) than α’_H-C₂S in B-BYF (~20 to 30%). The phase assemblage evolution has been determined by LXRPD coupled with the Rietveld method and MAS-NMR. The formation of stratlingite is favoured by increasing the w/c ratio in both systems. Finally, the optimisation of fresh BYF pastes jointly with the reduction of water-to-cement ratio to 0.40 have allowed the achieving of mortars with compressive strengths over 40 MPa at 7 days in all systems. Moreover, the st-BYF mortar, where borax was externally added, achieved more than 70 MPa after 28 days. The main conclusion of this work does not support Lafarge’s approach of adding boron/borax to the raw meal of BYF cements. This procedure stabilises the alpha belite polymorph, but its reactivity, in these systems, is lower and the associated mechanical strengths poorer. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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29 pages, 10256 KiB

Open AccessArticle

Impact of Sulphate Ions Content on Performance of Maleic and Acrylic Superplasticizers in Cement Paste

by Elżbieta Janowska-Renkas

Materials 2021, 14(10), 2683; https://doi.org/10.3390/ma14102683 - 20 May 2021

Cited by 4 | Viewed by 1854

Abstract

The paper presents test results of the impact of sulphate ions from calcium sulphates: Hemihydrate, dihydrate and anhydrite, on rheological properties and hydration heat of cement pastes with, and without, superplasticizers, derivatives of maleic (SP-2) and acrylic (SP-1) acids. It is demonstrated that [...] Read more.

The paper presents test results of the impact of sulphate ions from calcium sulphates: Hemihydrate, dihydrate and anhydrite, on rheological properties and hydration heat of cement pastes with, and without, superplasticizers, derivatives of maleic (SP-2) and acrylic (SP-1) acids. It is demonstrated that cement pastes fluidity depends on superplasticizer chemical structure, and its effect is expressed by a hydrophilic coefficient. As maleic superplasticizers have flexible comb-like structure composed of a shorter backbone chain containing COO⁻ carboxylate groups and very long side chains, cement pastes showed higher fluidity than with acrylic superplasticizer with ladder-like structure, longer backbone chains with shorter side chains. SP-1 showing lower hydrophilicity coefficient and fewer COO⁻ groups was found to be less sensitive to increased sulphate ion content in pastes. However, with SP-2 with higher hydrophilicity, a gradual fluidity loss (increased paste viscosity) was observed. Plastic viscosity was approximately at the same level in SP-1-containing pastes. Tests showed that sulphates definitely changed polycarboxylate superplasticizers performance. A high concentration of sulphate ions reduced maleic superplasticizer efficiency. Under these conditions, SP-1 is more effective and therefore more suitable for fluidity of pastes containing higher SO₄²⁻ ions content. Thus, sulphate ions concentration in the paste should be considered when selecting superplasticizer. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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19 pages, 5413 KiB

Open AccessArticle

Experimental Study on the Mechanical Properties and Compression Size Effect of Recycled Aggregate Concrete

by Yubing Du, Zhiqing Zhao, Qiang Xiao, Feiting Shi, Jianming Yang and Peiwei Gao

Materials 2021, 14(9), 2323; https://doi.org/10.3390/ma14092323 - 29 Apr 2021

Cited by 14 | Viewed by 1903

Abstract

To explore the basic mechanical properties and size effects of recycled aggregate concrete (RAC) with different substitution ratios of coarse recycled concrete aggregates (CRCAs) to replace natural coarse aggregates (NCA), the failure modes and mechanical parameters of RAC under different loading conditions including [...] Read more.

To explore the basic mechanical properties and size effects of recycled aggregate concrete (RAC) with different substitution ratios of coarse recycled concrete aggregates (CRCAs) to replace natural coarse aggregates (NCA), the failure modes and mechanical parameters of RAC under different loading conditions including compression, splitting tensile resistance and direct shear were compared and analyzed. The conclusions drawn are as follows: the failure mechanisms of concrete with different substitution ratios of CRCAs are similar; with the increase in substitution ratio, the peak compressive stress and peak tensile stress of RAC decrease gradually, the splitting limit displacement decreases, and the splitting tensile modulus slightly increases; with the increase in the concrete cube’s side length, the peak compressive stress of RAC declines gradually, but the integrity after compression is gradually improved; and the increase in the substitution ratio of the recycled aggregate reduces the impact of the size effect on the peak compressive stress of RAC. Furthermore, an influence equation of the coupling effect of the substitution ratio and size effect on the peak compressive stress of RAC was quantitatively established. The research results are of great significance for the engineering application of RAC and the strength selection of RAC structure design. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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21 pages, 4139 KiB

Open AccessEditor’s ChoiceArticle

Experimental Study on Biaxial Dynamic Compressive Properties of ECC

by Shuling Gao and Guanhua Hu

Materials 2021, 14(5), 1257; https://doi.org/10.3390/ma14051257 - 06 Mar 2021

Cited by 3 | Viewed by 1916

Abstract

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength [...] Read more.

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10⁻⁴, 10⁻³ and 10⁻² s⁻¹. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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10 pages, 1303 KiB

Open AccessArticle

The Rheometric Analysis of the Polymer Modifier’s Properties in the Environment of Hydrated Cement

by Khrystyna Moskalova, Aleksej Aniskin, Goran Kozina and Božo Soldo

Materials 2021, 14(5), 1064; https://doi.org/10.3390/ma14051064 - 24 Feb 2021

Cited by 4 | Viewed by 1774

Abstract

This paper investigates the effect of polymer modifiers (re-dispersible powder, multifunctional additives, methylhydroxyethylcellulose) on the rheological behavior of emulsions, saturated of calcium hydrosilicates to simulate a hydrating cement structure. The subjects of the study were modified emulsions which had varied concentrations of each [...] Read more.

This paper investigates the effect of polymer modifiers (re-dispersible powder, multifunctional additives, methylhydroxyethylcellulose) on the rheological behavior of emulsions, saturated of calcium hydrosilicates to simulate a hydrating cement structure. The subjects of the study were modified emulsions which had varied concentrations of each additive and they were examined comparatively to a base emulsion. Tests were performed with a CR-rheometer (“Himpribor-1”, Tula, Russia) applying the Searle measuring principle at various shear rates to characterize viscosity properties. The performance of modified mixtures within the operating period was analyzed by using two parameters—effective viscosity (η) and the proportion of structural failure (|m|). The test results showed that the most important factor influencing rheological characteristics is the addition of methylhydroxyethylcellulose additive—the higher additive amount in the emulsion, the higher the viscosity. Furthermore it was noted in the work that adding olefin sulfonate sodium salt causes reduced viscosities as well as lower shear moduli. If ethylhydroxyethylcellulose and ethylene vinyl acetate additives are used in the same mixture together, the rate of structural failure |m| can be relatively similar and low regardless of whether the mixture has large or small viscosity values. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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17 pages, 2973 KiB

Open AccessArticle

New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash

by Ana María Moreno de los Reyes, José Antonio Suárez-Navarro, Maria del Mar Alonso, Catalina Gascó, Isabel Sobrados and Francisca Puertas

Materials 2021, 14(3), 475; https://doi.org/10.3390/ma14030475 - 21 Jan 2021

Cited by 5 | Viewed by 1599

Abstract

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are [...] Read more.

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). ²²⁶Ra, ²³²Th and ⁴⁰K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for ²²⁶Ra, ²¹²Pb, ²³²Th and ⁴⁰K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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