Abstract The hydration behavior of C 2A 7, a component of many calcium aluminate cements, has been studied over a range of temperature using conduction calorimetry, X-ray and thermal analysis techniques. At 4°C, hydration occurs about 2 hours after mixing; hydration is slower at 20°C but at 40°C a very rapid reaction is observed. The initial hydration products are C 2AH 3 together with CAH 10 or alumina gel; considerable amounts of amorphous material are always also formed. At 20°C and above these initial products slowly convert to C 3AH 6; the conversion becomes faster with increasing temperature. The enthalpies of the hydration and conversion reactions were measured by conduction calorimetry.