The Experts below are selected from a list of 1110 Experts worldwide ranked by ideXlab platform
Aly Ahmed - One of the best experts on this subject based on the ideXlab platform.
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effect of cyclic loading on the compressive strength of soil stabilized with Bassanite tire mixture
Journal of Material Cycles and Waste Management, 2018Co-Authors: Aly Ahmed, Hesham El M NaggarAbstract:This study investigates the effect of static and cyclic loading on the performance of soil stabilized with recycled Bassanite, produced from gypsum wastes, mixed with waste tire shreds. Recycled Bassanite was mixed with furnace cement in different proportions to prevent the solubility of Bassanite. Different percentages by weight of this admixture were mixed with the test soil. In addition, different percentages and sizes of waste tire shreds along with a fixed content of Bassanite admixture were mixed with the tested soil. The static and cyclic strength and stiffness parameters of soil specimens treated using the different schemes were measured from cyclic triaxial tests. The results obtained showed that recycled Bassanite improved the strength of the treated soil, but the increase in compressive strength was much higher compared to the tensile strength. The strength of the treated soil increased as the admixture content and proportion of cement in the admixture increased. Shredded waste tire improved the tensile strength of the treated soil, but slightly reduced its compressive strength. Cyclic loading resulted in significant degradation of strength for samples treated with Bassanite admixture; however, incorporation of shredded tire reduced this degradation. It was also noted that the size of shredded tire had negligible effect on cyclic strength of the treated soil. The results also showed that the fatigue life of stabilized soil increased with the increase of shredded tire content and Bassanite admixture. As expected, the number of load cycles had a negative effect on the strength of treated soil: as the number of load cycles increased the strength degradation increased for both treated and untreated soil samples. The effect of number of cycles was more pronounced in the case of unreinforced soil sample while it reduced when tire shreds were incorporated in soil mixture.
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Effect of cyclic loading on the compressive strength of soil stabilized with Bassanite–tire mixture
Journal of Material Cycles and Waste Management, 2017Co-Authors: Aly Ahmed, M. Hesham El NaggarAbstract:This study investigates the effect of static and cyclic loading on the performance of soil stabilized with recycled Bassanite, produced from gypsum wastes, mixed with waste tire shreds. Recycled Bassanite was mixed with furnace cement in different proportions to prevent the solubility of Bassanite. Different percentages by weight of this admixture were mixed with the test soil. In addition, different percentages and sizes of waste tire shreds along with a fixed content of Bassanite admixture were mixed with the tested soil. The static and cyclic strength and stiffness parameters of soil specimens treated using the different schemes were measured from cyclic triaxial tests. The results obtained showed that recycled Bassanite improved the strength of the treated soil, but the increase in compressive strength was much higher compared to the tensile strength. The strength of the treated soil increased as the admixture content and proportion of cement in the admixture increased. Shredded waste tire improved the tensile strength of the treated soil, but slightly reduced its compressive strength. Cyclic loading resulted in significant degradation of strength for samples treated with Bassanite admixture; however, incorporation of shredded tire reduced this degradation. It was also noted that the size of shredded tire had negligible effect on cyclic strength of the treated soil. The results also showed that the fatigue life of stabilized soil increased with the increase of shredded tire content and Bassanite admixture. As expected, the number of load cycles had a negative effect on the strength of treated soil: as the number of load cycles increased the strength degradation increased for both treated and untreated soil samples. The effect of number of cycles was more pronounced in the case of unreinforced soil sample while it reduced when tire shreds were incorporated in soil mixture.
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Swelling and geo-environmental properties of bentonite treated with recycled Bassanite
Applied Clay Science, 2016Co-Authors: Aly Ahmed, M. Hesham El NaggarAbstract:Abstract This paper describes an investigation of the use of recycled Bassanite, which is derived from plasterboard waste, as an additive material to mitigate the swelling potential of bentonite considering its environmental impact. Recycled Bassanite was mixed with furnace cement and with lime at 2:1 ratios, and then the admixture was mixed with the tested bentonite at four different content ratios. The effects of adding Bassanite admixture on the swelling properties, mechanical properties, environmental properties, microstructure, and mineralogical composition of the tested bentonite were investigated. The test results indicated that recycled Bassanite has the potential for use as a stabiliser to mitigate swelling in expansive clay. Increasing the admixture content reduced the potential for swelling, the plasticity, the montmorillonite intensity, the percentage of sodium ions and the cation exchange capacity of the bentonite. The compressive strength, unit weight and percentage of calcium ions were increased for all admixture contents used. The different Bassanite–cement/lime admixture contents resulted in approximately the same reduction in the swelling potential of the tested bentonite. The Bassanite–cement/lime admixture had much more pronounced effects on the swelling and mechanical properties of the bentonite than Bassanite alone. The bentonite treated with 6% admixture content exhibited the greatest reduction in swelling potential; hence, this admixture content ratio is considered optimal for stabilising bentonite and mitigating its swelling. The measurements of hydrogen sulphide gas, fluorine solubility and pH of the treated bentonite were found to be within the acceptable limits, indicating that Bassanite–cement/lime admixtures used did not have any negative environmental effects. However, Bassanite is not recommended for use alone as an amendment for expansive clay because it releases fluorine at amounts that may exceed the allowable limit in some cases.
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On the compressive strength and geo-environmental properties of MC-clay soil treated with recycled Bassanite
International Journal of Civil Engineering, 2015Co-Authors: M. Kobayashi, Usama Hamed Issa, Aly AhmedAbstract:The use of recycled Bassanite, produced from gypsum wastes, in ground improvement projects is initiated recently in Japan to eliminate the huge quantities of gypsum wastes. Meanwhile the use of recycled Bassanite has a positive effect on the environment and economy, it has many challenges. These challenges are related to the release of fluorine more than the standard limits results in contaminated fluorine soil. This research investigates the effect of the amount of Bassanite, and water content on the release of fluorine from MC-clay soil stabilized with Bassanite, taking in consideration their effect on the compressive strength. Recycled Bassanite was mixed with furnace cement with a ratio of 1:1 to prevent the solubility of Bassanite. Different amounts of this admixture were mixed with the tested soil at different water contents. Unconfined compression test was used to determine the compressive strength while the solubility of fluorine was used to represent the geoenvironmental properties in term of the release of fluorine. Scan electron microscopic (SEM) test was done to identify the development of cementation compounds in the matrix of treated-Bassanite soil. Test results showed that, the addition of Bassanite had a significant effect on the improvement of compressive strength by increasing the amount of Bassanite. Curing time had a significant effect on the increase of compressive strength, the strength increases with the increase of curing time, especially in the later curing time. The release of fluorine increases with increasing the amount of Bassanite in soil mixture. The increase of water content had an indirect effect on the release of fluorine while it had a negative effect on the improvement of strength and consuming the amount of admixture. The increase of strength is associated with the decrease of the release of fluorine. Recycled Bassanite, produced from gypsum wastes, had a potential to be used as a stabilizer material for MC-clay soil and meet the standards of environment.
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Compressive strength and microstructure of soft clay soil stabilized with recycled Bassanite
Applied Clay Science, 2015Co-Authors: Aly AhmedAbstract:Abstract This paper investigates the microstructure and mineralogical compositions of soft clay soil stabilized with Bassanite that is produced from gypsum waste materials. Bassanite was mixed in different ratios with cement and lime, as a solidification agent, to prevent the solubility of Bassanite. Different amounts of these admixtures were mixed with the tested soil. Scan electron microscopic (SEM) and X-ray diffraction (XRD) were used to identify the microstructure and mineralogical compositions of stabilized soil specimens, respectively while unconfined compression test was used to examine the compressive strength. Test results showed that the addition of recycled Bassanite improves the strength of the tested soil. The improvement in the soil strength, based on compressive strength, is in agreement with the SEM and XRD results. The XRD results revealed the presence of various cementation compounds in the soil matrix when recycled Bassanite was added. Both the content and ratio of the admixture had a significant effect on the formation of the cementation compounds and the improvement of compressive strength. The formation of ettringite increased with the increase of admixture content in soil mixture for both admixtures used. The ratio of admixture had a clear effect on the reduction of the formation of ettringite in the case of Bassanite–cement admixture while it had no significant effect in the case of Bassanite–lime admixture. Curing time had a significant effect on the formation of ettringite and the improvement of compressive strength. These results support the suitability of using recycled Bassanite produced from gypsum wastes as a low cost and efficient stabilizer material in ground improvement projects.
Isabel Santacruz - One of the best experts on this subject based on the ideXlab platform.
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Tailored setting times with high compressive strengths in Bassanite calcium sulfoaluminate eco-cements
Cement and Concrete Composites, 2016Co-Authors: Marta García-maté, Enrique R Losilla, Miguel A G Aranda, Diana Londono-zuluaga, A.g. De La Torre, Aurelio Cabeza, Isabel SantacruzAbstract:Abstract This work deals with the hydration of a calcium sulfoaluminate (CSA) eco-cement prepared with Bassanite and different additives (type and content) at a fixed water/CSA ratio of 0.5. Pastes prepared with Bassanite show high water demands, high viscosity values and short initial setting times which are related to the fast dissolution rate of Bassanite and the subsequent precipitation of gypsum. These facts have a dramatic effect onto the mechanical strength values, and make necessary the addition of additives. Here, the addition of different amounts of specific retarders (polycarboxylate, tartaric acid and phosphonic acid) not only improved the workability of pastes and mortars, but also delayed the setting time by modifying the dissolution rates of the phase(s), and improved mechanical strengths. Finally, mortars with high compressive strengths (46 and 84 MPa at 1 and 7 days of hydration, respectively) and, chiefly, tailored setting times with high strengths have been prepared.
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Effect of calcium sulfate source on the hydration of calcium sulfoaluminate eco-cement
Cement & Concrete Composites, 2015Co-Authors: Marta García-maté, Enrique R Losilla, Laura Leon-reina, Angeles G. De La Torre, Miguel A G Aranda, Isabel SantacruzAbstract:Abstract The availability of cements, including eco-cements, with tailored mechanical properties is very important for special applications in the building industry. Here we report a full study of the hydration of calcium sulfoaluminate eco-cements with different sulfate sources (gypsum, Bassanite and anhydrite) and two water/cement ratios (0.50 and 0.65). These parameters have been chosen because they are known to strongly modify the mechanical properties of the resulting mortars and concretes. The applied multi-technique characterization includes: phase assemblage by Rietveld method, evolved heat, conductivity, rheology, compressive strength and expansion/retraction measurements. The dissolution rate of the sulfate sources is key to control the hydration reactions. Bassanite dissolves very fast and hence the initial setting time of the pastes and mortars is too short (20 min) to produce homogeneous samples. Anhydrite dissolves slowly so, at 1 hydration-day, the amount of ettringite formed (20 wt%) is lower than that in gypsum pastes (26 wt%) (w/c = 0.50), producing mortars with lower compressive strengths. After 3 hydration-days, anhydrite pastes showed slightly larger ettringite contents and hence, mortars with slightly higher compressive strengths. Ettringite content is the chief parameter to explain the strength development in these eco-cements.
Gui-yu Zhang - One of the best experts on this subject based on the ideXlab platform.
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increasing the early strength of high volume hwangtoh cement systems using Bassanite
Journal of building engineering, 2020Co-Authors: Run-sheng Lin, Ki-bong Park, Xiao-yong Wang, Gui-yu ZhangAbstract:Abstract Calcined Hwangtoh (HT) clay is a potentially viable supplementary cementitious material. However, using large amounts of HT significantly reduces the early strength of concrete, and this problem has yet to be addressed. We explored the effectiveness of improving the early strength of cement–HT systems by using Bassanite (calcium sulfate hemihydrate, CaSO4·0.5H2O) to activate HT. The effects of different contents (0–4 wt.%) of Bassanite on the mechanical properties, hydration reaction, and microstructure of high-volume (45 wt%) HT–cement systems were investigated. The experimental results show that the addition of Bassanite to HT–cement systems facilitates the formation of ettringite crystals in the early stage, thereby increasing the early strength. After one day, the compressive strength of the paste with a Bassanite addition of 3% increased by 82.3% compared with the paste without Bassanite, and no significant effect on the later strength was observed. However, for a Bassanite addition of >4%, excessive sulfate causes poor volume stability, leading to substantial reductions in the compressive strength at later stages.
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Increasing the early strength of high-volume Hwangtoh–cement systems using Bassanite
Journal of Building Engineering, 2020Co-Authors: Run-sheng Lin, Ki-bong Park, Xiao-yong Wang, Gui-yu ZhangAbstract:Abstract Calcined Hwangtoh (HT) clay is a potentially viable supplementary cementitious material. However, using large amounts of HT significantly reduces the early strength of concrete, and this problem has yet to be addressed. We explored the effectiveness of improving the early strength of cement–HT systems by using Bassanite (calcium sulfate hemihydrate, CaSO4·0.5H2O) to activate HT. The effects of different contents (0–4 wt.%) of Bassanite on the mechanical properties, hydration reaction, and microstructure of high-volume (45 wt%) HT–cement systems were investigated. The experimental results show that the addition of Bassanite to HT–cement systems facilitates the formation of ettringite crystals in the early stage, thereby increasing the early strength. After one day, the compressive strength of the paste with a Bassanite addition of 3% increased by 82.3% compared with the paste without Bassanite, and no significant effect on the later strength was observed. However, for a Bassanite addition of >4%, excessive sulfate causes poor volume stability, leading to substantial reductions in the compressive strength at later stages.
Wolfgang Voigt - One of the best experts on this subject based on the ideXlab platform.
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water channel structure of Bassanite at high air humidity crystal structure of caso4 0 625h2o
Acta Crystallographica Section B-structural Science, 2011Co-Authors: Horst Schmidt, Iris Paschke, Daniela Freyer, Wolfgang VoigtAbstract:Structure analysis using single-crystal diffraction was carried out as a contribution to the dispute about the nature of the water channel structure of Bassanite (CaSO4·0.5H2O). A recent result of Weiss & Brau (2009) for the crystal structure of Bassanite (monoclinic, space group C2) at ambient conditions of air humidity was confirmed. In the presence of high relative air humidity the crystal structure of Bassanite transformed due to the incorporation of additional water of hydration. The crystal structure of CaSO4·0.625H2O was solved by single-crystal diffraction at 298 K and 75% relative air humidity. The experimental results provided an insight into both crystal structures. A model explaining the phase transition from CaSO4·0.625H2O to CaSO4·0.5H2O was derived. The monoclinic cell setting of CaSO4·0.5H2O and the trigonal cell setting of CaSO4·0.625H2O were confirmed by powder diffraction.
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Water channel structure of Bassanite at high air humidity: crystal structure of CaSO4·0.625H2O.
Acta Crystallographica Section B Structural Science, 2011Co-Authors: Horst Schmidt, Iris Paschke, Daniela Freyer, Wolfgang VoigtAbstract:Structure analysis using single-crystal diffraction was carried out as a contribution to the dispute about the nature of the water channel structure of Bassanite (CaSO4·0.5H2O). A recent result of Weiss & Brau (2009) for the crystal structure of Bassanite (monoclinic, space group C2) at ambient conditions of air humidity was confirmed. In the presence of high relative air humidity the crystal structure of Bassanite transformed due to the incorporation of additional water of hydration. The crystal structure of CaSO4·0.625H2O was solved by single-crystal diffraction at 298 K and 75% relative air humidity. The experimental results provided an insight into both crystal structures. A model explaining the phase transition from CaSO4·0.625H2O to CaSO4·0.5H2O was derived. The monoclinic cell setting of CaSO4·0.5H2O and the trigonal cell setting of CaSO4·0.625H2O were confirmed by powder diffraction.
Marta García-maté - One of the best experts on this subject based on the ideXlab platform.
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Tailored setting times with high compressive strengths in Bassanite calcium sulfoaluminate eco-cements
Cement and Concrete Composites, 2016Co-Authors: Marta García-maté, Enrique R Losilla, Miguel A G Aranda, Diana Londono-zuluaga, A.g. De La Torre, Aurelio Cabeza, Isabel SantacruzAbstract:Abstract This work deals with the hydration of a calcium sulfoaluminate (CSA) eco-cement prepared with Bassanite and different additives (type and content) at a fixed water/CSA ratio of 0.5. Pastes prepared with Bassanite show high water demands, high viscosity values and short initial setting times which are related to the fast dissolution rate of Bassanite and the subsequent precipitation of gypsum. These facts have a dramatic effect onto the mechanical strength values, and make necessary the addition of additives. Here, the addition of different amounts of specific retarders (polycarboxylate, tartaric acid and phosphonic acid) not only improved the workability of pastes and mortars, but also delayed the setting time by modifying the dissolution rates of the phase(s), and improved mechanical strengths. Finally, mortars with high compressive strengths (46 and 84 MPa at 1 and 7 days of hydration, respectively) and, chiefly, tailored setting times with high strengths have been prepared.
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Effect of calcium sulfate source on the hydration of calcium sulfoaluminate eco-cement
Cement & Concrete Composites, 2015Co-Authors: Marta García-maté, Enrique R Losilla, Laura Leon-reina, Angeles G. De La Torre, Miguel A G Aranda, Isabel SantacruzAbstract:Abstract The availability of cements, including eco-cements, with tailored mechanical properties is very important for special applications in the building industry. Here we report a full study of the hydration of calcium sulfoaluminate eco-cements with different sulfate sources (gypsum, Bassanite and anhydrite) and two water/cement ratios (0.50 and 0.65). These parameters have been chosen because they are known to strongly modify the mechanical properties of the resulting mortars and concretes. The applied multi-technique characterization includes: phase assemblage by Rietveld method, evolved heat, conductivity, rheology, compressive strength and expansion/retraction measurements. The dissolution rate of the sulfate sources is key to control the hydration reactions. Bassanite dissolves very fast and hence the initial setting time of the pastes and mortars is too short (20 min) to produce homogeneous samples. Anhydrite dissolves slowly so, at 1 hydration-day, the amount of ettringite formed (20 wt%) is lower than that in gypsum pastes (26 wt%) (w/c = 0.50), producing mortars with lower compressive strengths. After 3 hydration-days, anhydrite pastes showed slightly larger ettringite contents and hence, mortars with slightly higher compressive strengths. Ettringite content is the chief parameter to explain the strength development in these eco-cements.