Effect of Shrinkage-Reducing Admixtures on the Shrinkage and Hydration of Cement-Based Materials

摘要

In this paper, the effect of shrinkage reducing admixtures (SRA) on autogenous shrinkage and drying shrinkage of cement paste were studied. The results indicated that SRA could reduce the autogenous and drying shrinkage effectively, and with increasing curing age, the shrinkage-reducing ratio reduced. In order to investigate the effect of SRA on the hydration process of cement-based materials, hydration heat, chemically combined water and Ca(OH)_2 content of paste, with and without SRA, were studied by isothermal calorimeter, gravimetric analysis and XRD. The results indicated that SRA had a slight retarding effect on the hydration of cement, but the degree of hydration tended to be the same with prolonged curing, which displayed as that SRA retarded the time of the exothermic peak, and reduced the peak value and hydration heat of cement. The chemically combined water content of SRA paste was less than that of the control sample and the difference in hydration between these two pastes were shortened with hydration age. The Ca(OH)_2 content of SRA paste was clearly less than that of control paste at 3 d, but was similar at 28 d. In addition, the existence forms of SRA in pore solution were proposed, and the mechanism of retarding hydration and the part of SRA affected shrinkage was also analyzed.