Strength and Heat of Hydration

The reaction of cement with water to produce hydration products releases heat, known as the heat of hydration.

Initially, heat generation is rapid due to the hydration of aluminates and silicates in cement. A sudden drop follows as hydration products coat silicates, then a gradual increase as remaining silicates react after dissolution of the coating, followed by a decrease and eventual stabilization as hydration slows.

The compounds in the cement contribute to its heat of hydration; C3A contributes the most, and C2S contributes the least.

For Portland cement, about fifty percent of the total heat is liberated between one and three days, about seventy-five percent in seven days, and nearly ninety percent in six months.

The C-S-H formed during the hydration of silicates in cement contributes to its strength.

Considering the variation in the strength of hydrated cement with time, hydration of C3S contributes more to the strength development during the first four weeks, while the hydration of C2S contributes to the strength gained thereafter.

However, by about one year, hydration of both C3S and C2S equally contribute to the gain in strength.

In contrast, the hydration of C3A and C4AF contribute little to the strength.