The utilisation of fly ash in cement and concrete is gaining immense importance today, mainly on account of the ecological benefits and the improvements in the long-term durability of concrete. The authors, while explaining the production process and characteristics of fly ash, have highlighted the use of fly ash in bricks,  concrete, high volume flyash concrete, roads and embankments, etc. An overview of the Indian scenario as well as the role of the fly ash in the clean development mechanism are also presented.

India is a resourceful country for fly ash generation with an annual output of over 100 million tonnes, registering almost 50 percent escalation over the last decade. Though utilisation of fly ash has been a subject of great concern in India for the past two and half decades, its use has picked up during the last five to six years, recording 15 to 18 percent use.Nevertheless, targets are very high against the generation that may touch 120 million tonnes per annum in the coming decade.

Of all the applications, the role of fly ash as a value-added complement to cement is the holistic approach and more tangible for durability enhancement of structures, leading to a voluminous consumption. This feature is tapped by FaL-G (Fly ash-lime-gypsum) technology for the proliferation of fly ash brick plants all over the country. The success lies in realising that Indian fly ashes are one of the best lots in the world to manufacture high strength concretes. 

Technologically, the performance of fly ash has been established way back in 1948 in the construction of Hungry Horse dam in the United States. Utilisation was upto 32 percent and fly ash was used for two phenomena, namely, reduced water demand to achieve the required workability and reduced heat of hydration of the concrete. Thereafter, these intricate properties were availed to address the durability problems of concrete which resulted out of high early strength cements, developed and used during post-II World War period. Fly ash has become an imminent input of concrete in many high-profile structures. 

When fly ash utilisation in India is analysed, an altogether different scenario emerges for the peculiar conditions prevailing in India,  such as:

• brick market is traditionally attached to the age-old clay bricks, vetoing chances for any alternate walling materials to penetrate on price logistics

• till the advent of FaL-G technology, autoclaved curing being the predominantly known art, no approach was economical to manufacture walling material with fly ash

• the poor quality of fly ash during the 70’s and the unscientific use of such fly ash in  a few pockets of cement industry had affected the credibility of pozzolanic cements with regard to durability that is haunting the confidence level in certain segments even today

• the ban on the use of pozzolana cement for structural applications, imposed by the Central Public Works Departments (CPWD) during the fall of 80’s, and reiterated in 1999, has given more room for consumers’ apprehensions, making the task tough forthe cement and concrete industry in promoting the product.

Since the beginning of the 90’s utilisation of fly ash attained new thrust from all segments of the country buttressed by many positive developments. Though India has to go a long way, the stage, set in the country, is poised to accomplish the target of putting to use over 100 million tonnes in the near future.