Tricalcium aluminate

Tricalcium Aluminate (also called C3A or Celite) (Al2O3 · 3CaO) is a chemical compound in the clinker of Portland cements (7% to 15%). Reacts very quickly with water, it is the one that possesses a reactive kinetics of greater speed between the silicate components of the clinker. The fast hydrated in the first minutes of the cement forge the aluminate crystals grow, contributing slightly to the resistance cement early in the concrete. characteristics

Aluminate crystals have a cubic structure with a = 1.5263 nm. When presented pure the proportion is 62.3% CaO, 37.7% Al2O3. The hydration rate is much higher than that of the cement clinker silicates (C3S and C2S). This capacity is lost in the presence of sodium ions, forming hydrates of hexagonal structure. Cements and concretes that exceed 10% of them are not suitable for marine environments (usually pozzolanic cement).

wiki