Influence of Aluminum Sulfate on Hydration and Properties of Cement Pastes

Abstract

This study evaluates the influence of aluminum sulfate (AS) on hydration and properties of cement pastes. The hydration behavior of cement paste contributed by AS was identified via isothermal calorimetry, X-ray diffraction (XRD), scanning electron microscope (SEM) and helium pycnometry. Setting time, compressive strength and pore structure of accelerated cement paste were also evaluated. Results indicate that the addition of AS can reduce setting time significantly and increase compressive strength of cement paste. Moreover, hydration process of accelerated cement paste can be divided into four stages according to absolute volume change measured by helium pycnometry, which are dissolution-crystallization stage, induction stage, rapid shrinkage stage and structure compacting stage. More nano-scale pores (pore diameter smaller than 10 nm) are generated in structure compacting stage, resulting in the “fake” absolute volume expansion. The rebound rate of shotcrete can be reduced with the increase of AS.