Dicalcium silicate (Ca 2SiO 4), also known as belite, is one of the major phases in Portland cement and certain calcium silicate cements. It hydrates more slowly than tricalcium silicate (C 3S), the other major component, producing calcium silicate hydrate (C-S-H) and lime (Ca(OH) 2) as byproducts over a longer period. This slower rate of hydration leads to a gradual development of strength, contributing significantly to the ultimate strength and durability of the cement. The presence of Ca 2SiO 4 is particularly important for the long-term performance of concrete, as its continued reaction helps improve strength over time, making it crucial under severe environmental conditions.