Cement

Types

Cement normally consists of a 30:20:1 ratio of calcium oxide, silicon dioxide, and gypsum. Some aluminum oxide can be substituted for silicon dioxide.

Portland Cement

C3S / Alite	50%	3CaO•SiO2	C3S + 6H = C-S-H + 3CH Alite + 6 Water = C-S-H + 3 Portlandite 2 (CaO)3SiO2 + 6 H2O → (CaO)3(SiO)2(OH)3 + 3 Ca(OH)2ΔH=-173.6	+120cal/g	very reactive compound, high heat of hydration, high early strength
C2S / Belite	25%	2CaO•SiO2	C2S + 4W = C-S-H + CH Belite + 4 Water = C-S-H + Portlandite (CaO)2SiO2 + 4 H2O → (CaO)3(SiO)2(OH)3 + CaOH	+62cal/g	low heat of hydration, slow reaction
C3A / Celite	10%	3CaO•Al2O3	C3A + CSH2 = Ettringite Celite + Gypsum = Ettringite (CaO)3Al2O3 + CaSO4 → (CaO)3(Al2O3)(CaSO4)3·32 H2O	+300cal/g	problems with sulfate attack, high heat of hydration
C4AF	10%	4CaO•Al2O3•Fe2O3			Absorbs excess sulfate to prevent it from poisoning other reactions
Gypsum	5%	CaSO4			used to control the set of cement

These materials form at 1450°C. The C-S-H component is what drives the wet-set to completion and results in the strong cement bond in the finished product.