SSC JE Civil Engineering 25-Sep-2019 Shift 1 Solved Paper

Properties of cement compounds
● Tricalcium aluminate, C${}_3$A:
It liberates a lot of heat during the early stages of hydration but has little strength contribution. Gypsum slows down the hydration rate of C${}_3$A. Cement low in C${}_3$A is sulfate resistant.
● Tricalcium silicate, C${}_3$ S:
This compound hydrates and hardens rapidly.
It is largely responsible for portland cement's initial set and early strength gain.
● Dicalcium silicate, C${}_2$S:
C${}_2$ S hydrates and hardens slowly. It is largely responsible for strength gain after one week.
● Ferrite, C${}_4$AF:
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.