Pozzolanic Reaction

Summary

Pozzolanic Reaction - The pozzolanic reaction occurs between pozzolans, Portland cement and water.

Technical Information

The pozzolanic reaction is between silica compounds in pozzolans and calcium hydroxide in Portland cement, to produce C-S-H. This reaction can only occur in the presence of calcium hydroxide; therefore pozzolans must be used in conjunction with Portland cement.
This reaction happens slower than the hydration of pure Portland cement, meaning concretes containing pozzolans tend to have a lower heat of hydration and lower early strength than concretes containing 100% Portland cement.

Pozzolans can also improve the concretes resistance to carbonation and sulphate attack as they reduce the calcium hydroxide available in the paste.