Why do we need Calcium hydroxide in concrete? Is it necessary there?
The calcium hydroxide is formed as the concrete hardens.
How concrete hardens
The dry concrete powder (Portland cement) is a mixture of several compounds.
The two most important ones are tricalcium silicate (
When water is added to cement, these compounds undergo hydration.
The reaction releases
Eventually, the system becomes saturated, and
You end up with a thick mass of crystals interlocked with each other and all the other substances present.
The effect of
Carbon dioxide from the air reacts with the calcium hydroxide in concrete to form calcium carbonate.
This reaction, called carbonatation, is a slow and continuous progression from the outer surface inward.
Carbonatation increases the mechanical strength of concrete, but it also decreases the pH.
Below pH 10, the passivated surface of the steel rebar dissolves, and the rebar starts to corrode.