The History of Fly Ash II

The team work between Fly Ash and Portland Cement

Fly Ash and Cement : A Dream Team

It is not only the chemistry provided by fly ash that compliments chemistry of cement, but also the physical properties of fly ash improve the rheology and microstructure of concrete by a great extent.

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!

Fly Ash + Cement = Space Shuttle

Here is a little parallel to illustrate the point. The hydration of Portland cement is like a rocket and Fly Ash is like a space shuttle.

The rocket of cement is required to pushg our Fly Ash shuttle up to a certain latitude. Once the fly Ash reaches that point, i can go on and on and on.....

What Does All This Mean?

In simple words, all this means a much longer life for our concrete structure.

Specific benchmarks have been set up to evaluate the performance of concrete with respect to durability?mainly Strength and Permeability. This means to produce a durable and long lasting concrete, it must posses: -

High strength
And
Low permeability

Fly ash makes concrete denser, and hence less permeable, mainly by : -

Reducing water demand in concrete
Improving microstructure of concrete

At the same time, fly ash improves long term strength of concrete due to the continued Pozzolanic reaction as discussed earlier. Following graph typically depicts the strength development with fly ash.

Ghatghar Dam : Maximum Impact

This is a first concrete dam of India built with roller compaction technology. Now, for a concrete dam, it is vital that the heat of hydration be reduced to the minimum. Who else could do this magic except fly ash?

The Bureau of Indian Standards restricts the replacement of cement to maximum 35% with fly ash. That means, Portland Cement always remains the Big Brother.

Look Who is Carrying Cement!!

...But the Ghatghar Roller Compacted Concrete Dam was a unique project in all respects. For the upper dam, 65% fly ash was used with 35% Portland cement. The result was much better than expected.

So Fly Ash was increased to 70% with only 30% of Portland cement!! Off corse, this was possible due to the roller compacting technology employed and definitely not be advised for other regular structures. Though, it is amazing to see how the younger one turns into the Big Brother and carries the elder one in his arms!!!