Powder mixed with water hardens, but not because the water evaporates. The powder dissolves in the water, the dissolved material precipitates as a different solid that has taken up water (a hydrate), and these solids join up. In ①, you watch calcined gypsum (β-hemihydrate gypsum) dissolve, the liquid become supersaturated with respect to dihydrate gypsum, and needle-like crystals appear and interlock. In ②, you watch C–S–H, calcium hydroxide, and ettringite grow around the particles of Portland cement and bind the particles together, along with the course of heat release. In ③, you put two cases side by side and compare how they set and how their pores differ when the ratio of water to powder is changed.
Mochizuki Research Group, Tokyo University of Science | The inside figures are schematic, and the scale is approximate. Solubilities, heats of hydration, densities, and Powers’ equations are literature values; the coefficients of the rate equations are provisional values for teaching, chosen to match the times in the literature (gypsum: Gurgul 2019 and Darmawan 2020; cement: Jagličić 2025 and Bentz 2006). To see how this differs from sintering, in which heating joins the powder, compare it with the sintering simulator. For detailed explanations and sources, see the explanation page (in Japanese) on the hydration of gypsum and cement. Back to: Mochizuki Research Group Education — Inorganic Materials Science > Virtual Experiments, Inorganic Materials Science resources