If the merits of fly ash are so well established and if it is available at about one fifth the cost of cement, then why are we consuming only about 38 per cent of the fly ash available in the country? ICR interacts with leaders in construction world to understand the benefits and finer points of using fly ash.
As much as 60 per cent of power in India is generated by burning coal. And looking at the vast reserves of coal available, it will continue to be the primary source of power in the country.
But coal-fired power stations make more than just power. In a way they are also making cement called "Fly Ash." You could also call a power station, a cement factory, having steam as its by-product. Unfortunately, rather than being seen as a resource, fly ash has been considered as industrial waste. Till about a decade ago it was being disposed of in ash ponds. The cement consumer industry still sees fly ash as a pollutant, which it is using for blending in cement/concrete and contributing to the betterment of environment while improving the strength of the construction material.
Fly ash is neither free nor is it cheap. At least not the good quality fly ash. Good quality fly ash is produced by passing the fly ash generated at the power stations through electrostatic precipitators. Here fly ash is screened and classified. Only 15-20 per cent of the fly ash screened is retained back and is considered as a superior quality material. The process, and the low yield of high quality fly ash, adds to cost.
Merits of fly ash are well known in the industry and it is being used as a partial cement replacement (on average 30 per cent) in structural concrete. Thus, today fly ash has become the fourth ingredient in concrete, next to cement, aggregate and water. Despite this realisation though, fly ash is still under utilised in the construction sector. One of the prime reasons is the lack of properly detailed standards pertaining to use of fly ash. Though there are various Indian Standards published by the Bureau of Indian Standards (BIS) that specify the use of fly ash as part replacement of cement in concrete, in actual practice the guidelines are still in nascent stage. During mid seventies and early eighties, the quality of fly ash was not that good due to high content of unburnt carbon and negligible awareness. The eighties ushered in the era of super thermal power stations. Equipped with high-efficiency boilers and coal mills, the quality of fly ash produced in these power stations was good. These improvements, however, were not communicated adequately. The doubts regarding using fly ash in cement probably have lingered too long, and even today it is not odd to find engineers hesitant to use fly ash in their mix. Besides, fly ash being a high volume low value product, transportation adds severe restrictions to its reach and use. It is not economically viable to use fly ash beyond a radius of 100 km from the point of production.
Considering the tremendous growth required in the power sector for the development of Indian economy, it is expected that ash generation will reach 225 million tonnes by 2017. The quality of fly ash produced in India is superior due to low sulphur and unburnt carbon content. Growth in infrastructure will create huge cement demand. And if encouraged properly, fly ash can provide for at least 30 per cent of this demand. Using fly ash is economical too. Shailesh Puranik, Managing Director, Puranik Builders, puts it in numbers stating that, "Fly ash reduces 20 per cent of cement cost in a project. Today fly ash costs about Rs 50 to Rs 60 per bag, while cement on an average is sold at Rs 250-300 per bag. Fly ash reduces the construction cost by about Rs 10-15 per sq.ft. On top of that projects based on fly ash utilisation receive green credits that could be traded." That leaves us with no reason not to use fly ash when available.
Today utilisation of fly ash is limited mainly due to lack of required information to actual users like State/Central Governments, construction departments, builders, developers, etc. There is a need to communicate these benefits to todays nation builders. In a series of interviews that follow, we look at the benefits of using fly ash and the parameters to examine while picking up the right product.
Benefits of using fly ash
- Reduced permeability of the structure to water and aggressive chemicals
- Reduction in the amount of water needed for mixing
- Consumes fly ash, which is other wise dumped in fly ash ponds leading to pollution
- Serves as a substitute to cement which is about five times costlier than fly ash.