The hydration of cement is an exothermic reaction in which heat is generated as cement hydrates. This heat of hydration is critical to cement's strength development. The rate at which this heat is generated affects the temperature rise, with a majority of the heat being released early in the hydration process, half within the first three days, and about 75% within the first week.
The heat of hydration for each cement compound is significant; for instance, tricalcium aluminate (C3A) and tricalcium silicate (C3S) contribute most to this process. Table 1 summarizes the heat of hydration for cement compounds like C3S, C2S, C2A, and C4A. Adjusting the proportions of these compounds can manage the rate and total amount of heat released during cement hydration.
Table 1. Heat of Hydration for Cement Compounds
| Compound | Heat of hydration (J/kg) |
| C3A | 867 |
| C3S | 502 |
| C4AF | 419 |
| C2S | 260 |
The strength development of hydrated cement is primarily influenced by the compounds tricalcium silicate (C3S) and dicalcium silicate (C3S). C3S contributes significantly to the strength during the initial four weeks after hydration, while C2S plays a more crucial role in the long-term strength gains, especially after the first year. After one year, both compounds, when considered on a mass-for-mass basis, contribute equally to the cement's overall strength.
