Fly Ash Concrete

Chemical Nature

Fly Ash

What is Fly Ash Historical Background Chemical Nature Classification
Chemical Composition Mechanical properties Benefits High Volume
Fly Ash
Need for extending Strength Specifications to beyond 28 days – Restraints on use of Fly Ash in Highway Constructions

Chemical Nature of Fly Ash

As much as 20 pounds of free lime is released during hydration of 100 pounds of cement.

This liberated lime forms the necessary ingredient for reaction with fly ash silicates to form strong and durable cementing compounds no different from those formed during hydration of ordinary portland cement.

The Hydration reactions of Ordinary Portland Cement without/with presence of Fly ash are as under:

hydration reaction of ordinary portland cement

The main benefit of fly ash in concrete is that it not only reduces the amount of non-durable calcium hydroxide (lime), but in the process converts it into calcium silicate hydrate (CSH), which is the strongest and most durable portion of the paste in concrete.

Fly ash also makes substantial contributions to workability, durability, chemical resistance and the environment.


Concrete-Techgroup thanks Headwaters Resources , USA for granting them permission to use their resources in developing this article.