Fly Ash: An Important Green Construction Resource

Most of the coal is carbon. It contains some quantities of non combustible minerals. When the coal is used as a fuel to generate the electricity in coal fired power plants. End products in the form of ash are obtained. These minerals remain in ash. Thus fly ash is a very fine powdery material that would fly out of plant, if not contained. This ash material is very valuable resource on one side on the contrary if not used or disposed properly become a nuisance for environment.

Technically speaking fly ash particles are glassy, spherical shaped even finer than cement particles. Cement particles are finer and are finely ground in order to get higher strength. The fly ash particles are naturally finer, microscopically viewing appears very spherical, whereas the cement particles are uneven when compared with fly ash particles.

Fly ash is most commonly used pozzolan in the world. The earliest forms of pozzolan were made with volcanic ashes near Pozzouli in Italy which later gave rise to the term pozzolan.

ACI, American Concrete Institute, defines fly ash as the finely divided residue resulting from the combustion of ground or powdered coal which is transported from the firebox through the boiler by flue gas.

The use of fly ash as construction material is not new. Long before the Portland cement was invented. 2000 years ago Roman people used volcanic ash to built Pantheon. Roman knew the cementing property of ash products.

Largest use of fly as is done in producing concrete. Conventionally concrete is a mixture of cement sand and aggregates. This conventional concrete gains strength when a chemical reaction is performed in the presence of water. A cementing material is produced, which is known as silica gel. It is coated around every particle, which hardens to gain strength. In this process whole quantity of cement is not fully utilized in reaction, some free lime still remains in concrete. This free lime erupts in the form of efflorescence and the durability of concrete is reduced.

In the presences of fly ash (when some part of the cement is replaced with fly ash) the free lime is fully converted into cementing material. This result in gaining of full strength in concrete and durability of concrete is increased.

The fly ash particles acting like lubricating balls, a perfect mix is obtained and concrete becomes highly workable. Fly ash being lighter in weight, reduced unit weight of the concrete helps it to be pumped easier over a longer distance.

Fly ash is a material can be recycled, its use has a very positive impact on the environment. Fly ash use decreases the land fill disposal. Fly ash use decreases the use of cement. As the production of cement releases Co2 gas in the atmosphere (One ton of cement produced releases one ton of co2 in the atmosphere). By replacing the cement with fly ash helps in maintaining the atmosphere positive because cement production is a major energy user and source of “green house gas”

Fly ash is also used in producing very strong high power concrete. Which is called self compacting concrete (SCC), requiring no vibrators to compact it. In turn avoiding use of labors (also called green concrete due to lesser operations and noise level).

Other uses of fly ash are, for increasing the strength of soil to be used for soil stabilization, fly ash fills roads, precast products like tiles and blocks, fly ash bricks also called green bricks , agricultural use , raising of dykes, mine filling etc.

Fly ash would play a major role due to its universal availability. Being a useful resource and making the world greener. Fly ash disposal shall continue to be an important area of national concern for all countries. Fly ash disposal management has undergone a considerable improvement over past few years.

Due to increasing environmental concern, it is very important to manage fly ash in a more efficient way, as fly ash has tremendous potential to be utilized.