Research Institute of Binding Materials Prague Ltd.
Abstract
ISSN: 2523-935XInternational audienceIt is admitted that the cement industry contributes for about 5-7% of the total man-made CO2 emissions. A possible way for decreasing these CO2 emissions is the development of alternative clinkers with lower proportion of limestone in the raw materials. Calcium sulfoaluminate cements (CSA) are regarded as a promising low CO2 alternative to Portland cements. Generally, with a sufficient amount of calcium sulfates, the main hydration product of these cements is ettringite, which strongly affects the workability of CSA pastes. Polycarboxylate superplasticizers (PCE), combined with retarders, can be used with the aim to decrease the yield stress and the viscosity of this type of pastes. However, the multitude of components of these cements makes it difficult to understand the effect of these additives on the hydration process and on the properties of pastes. The aim of this work is to provide a better understanding of the: (i) effect of the molecular structure and the dosage of PCE on the hydration and rheology of CSA (ii) effect of citric acid on the dispersing effectiveness of PCE . Three PCEs, with the same chemical structure but different molecular structure, were investigated. Vicat tests and isothermal calorimetry were used to describe the hydration process. While, Rheological properties were characterized with mini-cone tests. Adsorption measurements were carried out with Total Organic Carbon analyzer and ion chromatography. The results reveal a competitive adsorption between citric acid and PCEs, which decreases the dispersing effectiveness of the latter
