Properties of cement compounds ● Tricalcium aluminate, C3A: It liberates a lot of heat during the early stages of hydration but has little strength contribution. Gypsum slows down the hydration rate of C3A. Cement low in C3A is sulfate resistant. ● Tricalcium silicate, C3 S: This compound hydrates and hardens rapidly. It is largely responsible for portland cement's initial set and early strength gain. ● Dicalcium silicate, C2S: C2 S hydrates and hardens slowly. It is largely responsible for strength gain after one week. ● Ferrite, C4AF: This is a fluxing agent which reduces the melting temperature of the raw materials in the kiln (from 3,000° F to 2,600° F). It hydrates rapidly but does not contribute much to strength of the cement paste. Hence, the major compounds in Ordinary Portland Cement responsible for its strength aretricalcium silicate and dicalcium silicate.