3CaO·3Al 2O 3·CaSO 4, also known as tricalcium aluminate trisulfate, is a phase in calcium aluminate cements and sometimes forms in Portland cements. This compound is of particular interest in the study of cement’s behavior under sulfate environments. The mechanism of its action involves its reaction with water to form ettringite, which can contribute to the early strength of concrete but might also lead to durability issues under certain conditions like sulfate attack.