The Experts below are selected from a list of 78 Experts worldwide ranked by ideXlab platform
Wiesława Nocuń-wczelik - One of the best experts on this subject based on the ideXlab platform.
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Use of calorimetry and other methods in the studies of water reducers and Set Retarders interaction with hydrating cement paste
Construction and Building Materials, 2013Co-Authors: Wiesława Nocuń-wczelik, Przemysław CzapikAbstract:Abstract The calorimetric method was used as a main tool in the studies of the effect of superplasticizing and Set retarding admixtures on cement hydration. The experiments were carried out using two types of cements (neat Portland cement CEM I 42.5R and blended Portland cement type CEM II/B-M (S-V) 42.5N), at varying w/c ratio 0.5 and 0.3 respectively. The hampering of cement hydration process at early age in the presence of these admixtures was generally observed. This is in practice equivalent to the Set retardation. The dissolution, as well as the precipitation of hydration products were retarded too, as it has been proved by the DTA/TG, conductometric measurements and the evaluation of so-called chemical shrinkage. However in case of superplasticizers, after a prolonged “dormant” period the process is continued; the reactions occur at fairly good rate giving substantial heat effects – it can be concluded from the total heat evolved values after standard 41 h. At longer time a significant amounts of products are formed as well, but it seems that the crystallization of calcium oxide is disturbed; simultaneously the amount and composition of calcium silicate hydrates alters towards the “more amorphous” product. This could be observed under SEM. The Set Retarders give strong delaying effect, particularly at low amount of water and in the pastes produced from Portland cement. This can be due to the formation of insoluble layer of calcium and sugar or calcium and phosphorus containing compounds surrounding the hydrating grains; the formation of this “barrier” can be distinguished as a small peak on the calorimetric curve and it is poorly removable on further hydration. The shrinkage and conductivity measurements seem to prove not only the change of kinetics of heat evolution/hydration but also the modification of the process and resulting products.
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Application of calorimetry in studies of the immobilization of heavy metals in cementitious materials
Thermochimica Acta, 1995Co-Authors: Wiesława Nocuń-wczelik, Jan MałolepszyAbstract:Cementitious systems based on blends of normal portland cement with different materials are used for the treatment and conditioning of toxic and hazardous wastes. The addition of waste material may interfere with the hydration reaction in the cement matrix and consequently with the Setting and with hardening process. Some of the waste materials accelerate the hydration process, others act as Set Retarders. The progress of hydration can be monitored by heat evolution measurements and the calorimetric results are considered as indicators of the degree of hydration. In this study microcalorimetry was used to evaluate the heat output during the hydration of cement and of blends of cement and blast furnace slag treated with solutions of heavy metals.
Jan Małolepszy - One of the best experts on this subject based on the ideXlab platform.
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Application of calorimetry in studies of the immobilization of heavy metals in cementitious materials
Thermochimica Acta, 1995Co-Authors: Wiesława Nocuń-wczelik, Jan MałolepszyAbstract:Cementitious systems based on blends of normal portland cement with different materials are used for the treatment and conditioning of toxic and hazardous wastes. The addition of waste material may interfere with the hydration reaction in the cement matrix and consequently with the Setting and with hardening process. Some of the waste materials accelerate the hydration process, others act as Set Retarders. The progress of hydration can be monitored by heat evolution measurements and the calorimetric results are considered as indicators of the degree of hydration. In this study microcalorimetry was used to evaluate the heat output during the hydration of cement and of blends of cement and blast furnace slag treated with solutions of heavy metals.
F Fernandez - One of the best experts on this subject based on the ideXlab platform.
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Characterization of a more sustainable cement produced with recycled drywall and plasterboards as Set Retarders
Construction and Building Materials, 2016Co-Authors: Nelson Flores Medina, Xabier Arroyo, Amador Aguilera, Francisco Hernandez-olivares, F FernandezAbstract:Abstract This paper deals with the study of a process that allows the use of waste sulphates from drywalls and plasterboards in the cement chemistry without affecting the resistance of cement, since cement industry is an important sulphate consumer. The role of the recycling temperature to obtain recycled calcium sulphates (RCS) and their SO3 contents, when RCS are used as Set Retarders in cements, is also studied. Gypsum from drywalls, and plaster of Paris from plasterboards, were heated at three recycling temperatures (110 °C −150 °C −170 °C) and partially dehydrated to obtain RCS. Chemical composition and SO3 purity of these RCS and of natural gypsums were determined and compared via XRD and DSC/TG. Setting time, the compressive strengths and the microstructure of cements with RCS used as Set retarder were studied. The main products formed after cement hydration were determined by XRD and their microstructure observed by SEM/EDX. Internal porosity of different blends, area per mm2 and diameter distribution, was determined through image processing with computer-aided design (CAD) software in SEM images. Cements with RCS from plasterboards as Set retarder, with the higher SO3 content and higher amount of hemihydrates, preheated at 150–170 °C, have mechanical strengths according to cement standards. They show a denser microstructure, lower porosity and more homogeneous matrix after final Setting than cements with RCS from drywalls. The selection here suggested of waste sulphates and the preheating process will allow using recycled sulphates from debris in the cement industry, according to EU standards.
Stephen D. Kinrade - One of the best experts on this subject based on the ideXlab platform.
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Effects of saccharide Set Retarders on the hydration of ordinary portland cement and pure tricalcium silicate
Journal of the American Ceramic Society, 2010Co-Authors: Linghong Zhang, Raymond J. Balec, Andrew C. Larsen, Hassan Haji Esmaeili, Lionel J. J. Catalan, Stephen D. KinradeAbstract:The effects of aliphatic sugar alcohols (e.g., threitol, xylitol, sorbitol) on the hydration of tricalcium silicate (C3S) and ordinary portland cement (OPC) were investigated and compared with those of sucrose, a well-established cement Set retarder. Only sugar alcohols which contain threo diol functionality retarded the Setting of C3S and OPC, their efficacy increasing with the number of threo hydroxy pairs and, to a smaller extent, with the overall population of hydroxy groups. None, however, were as effective as sucrose. The initial and final Setting times increased exponentially with the concentration of saccharide, although the hydration of OPC was less inhibited than that of C3S. Saccharides function as “delayed accelerators,” that is, cement hydration is first inhibited and then proceeds faster than in saccharide-free cement. This behavior is consistent with the theory that the induction period is controlled by slow formation and/or poisoning of the stable calcium silicate hydrate (CSH) nuclei. The early inhibiting influence of saccharides on CSH precipitation is apparently stronger than on the growth of crystalline calcium hydroxide. Saccharides did not negatively affect the degree of hydration and compressive strength of fully Set OPC paste; on the contrary, sorbitol yielded modest increases.
Nelson Flores Medina - One of the best experts on this subject based on the ideXlab platform.
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Characterization of a more sustainable cement produced with recycled drywall and plasterboards as Set Retarders
Construction and Building Materials, 2016Co-Authors: Nelson Flores Medina, Xabier Arroyo, Amador Aguilera, Francisco Hernandez-olivares, F FernandezAbstract:Abstract This paper deals with the study of a process that allows the use of waste sulphates from drywalls and plasterboards in the cement chemistry without affecting the resistance of cement, since cement industry is an important sulphate consumer. The role of the recycling temperature to obtain recycled calcium sulphates (RCS) and their SO3 contents, when RCS are used as Set Retarders in cements, is also studied. Gypsum from drywalls, and plaster of Paris from plasterboards, were heated at three recycling temperatures (110 °C −150 °C −170 °C) and partially dehydrated to obtain RCS. Chemical composition and SO3 purity of these RCS and of natural gypsums were determined and compared via XRD and DSC/TG. Setting time, the compressive strengths and the microstructure of cements with RCS used as Set retarder were studied. The main products formed after cement hydration were determined by XRD and their microstructure observed by SEM/EDX. Internal porosity of different blends, area per mm2 and diameter distribution, was determined through image processing with computer-aided design (CAD) software in SEM images. Cements with RCS from plasterboards as Set retarder, with the higher SO3 content and higher amount of hemihydrates, preheated at 150–170 °C, have mechanical strengths according to cement standards. They show a denser microstructure, lower porosity and more homogeneous matrix after final Setting than cements with RCS from drywalls. The selection here suggested of waste sulphates and the preheating process will allow using recycled sulphates from debris in the cement industry, according to EU standards.