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Gypsum
A white powdery mineral, Calcium Sulphate Dihydrate, formed through calcination by heating calcium sulphate dihydrate to evaporate water and create crystallization.
Beta-hemihydrate
Formed at 110-120°C, with large irregular shaped orthorhombic crystal particles and capillary pores.
Alpha-hemihydrate
Formed at 125-130°C, with small regularly shaped smoother and denser crystalline particles in the form of prisms and rods.
Dissolution-Precipitation Theory
The process where hemihydrate dissolves, dihydrate recrystallizes, and crystals interlock to form the set solid.
Water/Powder Ratio (W/P)
The ratio of water to powder needed for the chemical reaction of crystallization in gypsum products.
Mixing Time (MT)
The time taken from adding the powder to water until mixing is complete.
Setting Expansion
The expansion that occurs as dihydrate crystals form, grow, and interlink in gypsum products.
Wet Strength
Strength of gypsum when excess water for hydration is present.
Dry Strength
Strength of gypsum when excess water has been dried off.
Compressive Strength
The strength of gypsum due to dissolved dihydrate precipitates and interlinked crystals, influenced by factors like porosity and water/powder ratio.
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