How does Cement Harden

What chemistry makes cement set?

Cement is a very fine powder made from limestone and clay, heated in a kiln to form binding compounds such as tricalcium silicate.

The terms cement and concrete are often used interchangeably, but they are not the same; cement is the binding ingredient used to make concrete. Tricalcium silicate in cement reacts with water, in a process called hydration, releasing calcium and hydroxide ions and a great deal of heat.

This heat perpetuates the reaction until the mix is saturated with the ions, at which point the calcium hydroxide begins to crystallise forming a more rigid structure. Crystals of calcium hydroxide begin to thicken making it harder for the water to reach the unhydrated tricalcium silicate. Therefore the reaction slows as the mixture sets.

The less water-to-cement ratio, the stronger the concrete will be.