Fly ash in concrete

           Fly ash is a fine powder which is a by-product of coal-fired electric generating plants which is considered to have a small environmental footprint, as no energy is required to manufacture it, which can be replaced in place of concrete. Fly ash is a pozzolan material & during the hydration of cement it forms cementitious material by reacting with lime in presence of moisture.

        Introduction of fly ash in concrete reduces the cement consumption as it acts as a cementitious material resulting in more economic mix design as it is a by-product. It also increases long-term strength, workability, flowability (The ability of concrete to flow freely) of the concrete.

Some advantages of using fly ash :-

1.    Produces various set times of Concrete:

The use of fly ash in concrete enables us to control of setting time of concrete, from 0- 10% fly ash content by weight of cementitious material doesn’t have any effect on initial & final setting time of concrete, however when the percentage of fly ash is more than 10% there is a rapid increase in initial setting time of concrete.

2.    Reduces heat of Hydration:

From total amount of cementitious material, a certain amount of cement replaced by fly ash reduces the heat of hydration & thus becomes necessary when doing mass concreting, as high heat of hydration can cause cracking & other defects in concrete. Concrete durability as well as long-term strength (I.e. greater than 56 days) is not affected the loss of heat.

3.    Produces high strength gains:

Fly ash enhances the strength of concrete but depending upon the percentage of use. The rate of effect of strength gain in concrete due to the addition of fly ash is slower than ordinary concrete without fly ash, however the long-term strength is higher.

4.    Fly ash is considered as a non-shrink material:

The use of fly ash in concrete also enhances the microstructure of cement paste due to the pozzolanic reaction which in turn decrease the chances of cracks, permeability & bleeding of concrete. Due to this fact the concrete protect against corrosion of reinforcement steel by making it less likely to let water flow through it.

5.    Produces dense concrete with a smooth surface and sharp detail:

Use of fly ash produces dense concrete which gives a smooth finish & sharp edges which give a better aesthetic view of the structure.

6.    Increases workability with lower water cement ratio than concrete without fly ash:

Use of fly ash in concrete increases workability with lower water cement ratio, fly ash particles are spherically shaped, giving the concrete a lubricating effect and lesser water demand, 25% fly ash in a concrete can reduce water demand by 6-10%. Due to these the pumpability of the concrete is greatly increased & reducing frictional loss during pumping.

             Use of admixture in normal concrete also increases the workability of the concrete, however after a certain amount the increase in admixture it is observed that the concrete starts bleeding. Use of fly ash will increase the workability of concrete additionally to the use of admixture. Practically project’s quality laboratory during conduction of concrete trials the difference in workability is clearly visible between concrete with & without the use of fly ash.