Fly Ash For Readymix

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What Is Fly Ash?

Fly ash is a by-product of burning pulverized coal in an electrical generating station. Specifically, it is the unburned residue that is carried away from the burning zone in the boiler by the flue gases and then collected by either mechanical or electrostatic precipitators.

Fly ash is used as a supplementary cementitious material (SCM) in the production of portland cement. Supplementary material when used in conjunction with portland cement contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity or both.

Fly ash has a high amount of silica and alumina in a reactive form. Reactive elements complement hydration chemistry of cement. When cement reacts with water, we say that hydration of cement has began and produces C-S-H Gel.

However, one more compound is produced on hydration that is so different in behaviour. It is non other than the Calcium Hydroxide Ca(OH)2. In construction industry, it is generally referred to as Free Lime.

Aggressive environmental agents like water, sulphates, CO2 attack this free lime leading to deterioration of the concrete.

Fly ash, on itself, can not react with water. It needs free lime, produced on hydration of Portland cement, to trigger off its Pozzolanic effect. Once it is triggered, it can go on and on!

Physical Aspect

The fly ash from the boilers where mechanical collectors are used is coarser than fly ash from electrostatic precipitators.

The color varies from light to dark grey depending upon its carbon contents

The quality of fly ash varies from source to source

Fly ash particles are small, they effectively fill voids

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