Effects of Polymers on Workability and Early Microstructure of Gypsum-Based Materials

In this study, the effects of carboxylated styrene butadiene rubber (SBR) and polyvinyl alcohol (PVA) on fluidity and setting time of gypsum-based material (GM) pastes were investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses were applied to study the early hydration and micro-structure of GM pastes, further revealing the working mechanism of two polymers. The results show that the hydrophobic SBR is mainly absorbed on gypsum particles, breaking up the flocculation structures and simultaneously hindering the hydration, therefore increasing the fluidity and prolonging the setting time of GM pastes; the hydrophilic PVA can adsorb free water and therefore reduce the effective water-gypsum ratio (W/G), which promotes the formation of flocculent structures and accelerates the hydration. However, PVA could be also absorbed on gypsum particles and hinder the hydration. As a result, PVA decreases the fluidity and has little influence on setting time of GM pastes. Keywords: gypsum; hydration; microstructure; polymer; setting.