Hydration characteristics and mechanism analysis of β-calcium sulfate hemihydrate

Abstract

Although the dissolution/precipitation mechanism for hemihydrate hydration is widely recognized, this study gives more detailed information for the hydration of hemihydrate by in-situ observation using environmental scanning electron microscope (ESEM). The hydration process was also monitored through numerous parameters, including phase, hydration degree, ion concentration, particle size, and morphology evolution with hydration time. The results indicated that the hemihydrate particles are porous containing numerous nanopores. It dissolves from the surface available to water, forming a transient flocculent intermediate with widen pores. Afterwards, large particles break to small particles due to crack connection and then continue to dissolve, leaving a few stubborn spots last to disappear. At the same time, gypsum precipitates in the first few minutes and evolves to the final crystal structure through three main stages. This work not only provides the most direct evidence for the hydration mechanism, but also gives new insights to enrich it further. It is helpful to adjust the hydration process of gypsum plaster and provide a significant reference for modeling.