Effect of particle size distribution on the hydration and compressive strength development of α-calcium sulfate hemihydrate paste

Particle size distribution (PSD) of α-calcium sulfate hemihydrate (α-HH) was quantitatively analyzed by Rosin–Rammler–Bennett (RRB) distribution function. The hydration of plaster and the compressive strength development of paste were correlated with the RRB parameters, focusing on the singular effect of particle fineness (described by the characteristic particle size, De) and distribution width (described by the uniformity coefficient, n) on the water–hemihydrate weight ratio (W/H) for standard consistency, hydration rate, compressive strength and microstructure of paste. The effect of particle fineness is more pronounced than that of distribution width. The microstructure details are in general agreement with the impact of PSD on the hydration and the compressive strength development of paste. The plaster with the optimum PSD hydrates completely without a hydration barrier at a relatively lower W/H for standard consistency. Then, homogeneous and well-grown calcium sulfate dihydrate (DH) crystals and a more compact structure are obtained, leading to a higher compressive strength. For pastes of standard consistency, an optimum PSD is characterized by De ≈ 35 μm and n ≈ 0.82.