Early hydration and microstructure of gypsum plaster revealed by environment scanning electron microscope

Early hydration and microstructure of gypsum plaster (G) paste in different compositions and hydration time were studied by environment scanning electron microscope (ESEM) coupled with liquid nitrogen cooling. It was observed that small hemihydrate particles rapidly dissolved and hydrated, forming dihydrate crystals network around large hemihydrate particles, which makes an increasingly dense microstructure and promotes the setting of G paste. Besides, different chemical admixtures such as polycarboxylate (PC), hydroxy propyl methyl cellulose (HPMC) and starch ether (SE) would promote the flocculating or deflocculating between particles and therefore modify the fluidity of the paste. This work paves the way to the understanding the setting and rheology of hydraulic materials in the perspective of microstructure evolution.