Fly Ash is a supplementary cementitious material (because of its pozzolanic character) for cement concrete. It is widely available and technically highly useful product. The cement contents, Fly Ash Concrete are more durable; actually durability level of Fly Ash Concretes can not de achieved in cement concretes. These aspects, besides, various benefits of usage of fly ash in cement concrete are discussed in this paper. It is concluded, based on the available information, that there is no need for any apprehension for use of fly ash and the Fly Ash Concretes are more eco-friendly and hence ‘greener’, due to their reduced energy contents, higher efficient use of Portland cement, lower cost per unit volume, and longer period of service life.
The current rapid development in India has created a large demand for construction for years to come, requiring increased production of cast-in-place concrete and concrete products. These will be essential to major infrastructure construction projects such as transportation (roads, bridges, airports), water distribution (embankments and water channels), energy development (nuclear power generation), and for buildings in general. Typically, conventional concrete is made of fine and coarse aggregates, water, Portland cement and chemical admixtures. Portland cement based composites have high potential for strength which are not utilized gainfully in the actual practice. Moreover, it has been conceded that the concrete is the largest man-made material of construction. To make the concrete more eco-friendly, its energy content should be reduced, its long-term durability superior and the ingredients environment-friendly. Therefore, it is essential to introduce new technologies and practices for alternative cement and concrete compositions in order to curtail the rising environmental problems caused by increased Portland cement production. Furthermore, these new technologies will slow down the depletion of raw material (mainly limestone) used for cement production. All these objectives can be easily achieved if the fly ash is used appropriately to partially replace Portland cement in concretes.
2.0. NECESSITY TO MAKE CONCRETE ECO-FRIENDLY
2.1. Under utilization
Concrete industry in the world is the largest consumer of natural resources, such as rock and sand (8 billion tones), and also one of the largest consumer of water (600 to 700 billion gallons). Cement forming binder of the concrete has very high energy content (1.3 kwH/kg) and its usage in concrete has to be as less as possible so that the final energy content of concrete is less. Portland cement being a very high-tech material can produce strength up to 800 MPa as against the conventional strength levels of about 30 to 60 MPa in construction. Thus, Portland cement is grossly under-utilized in normal constructions. Current Scenario
The cement industry is the India’s second highest payer of Central excise and major contributor to GDP. With infrastructure development growing and the housing sector booming, the demand for cement is likely to increase. The industry is extremely energy intensive - after thermal power plants and the iron and steel sector, the Indian cement industry is the third largest user of coal in the country. In 2003-04, 11,400 million kWh of power was consumed by the Indian cement industry. India is the second largest producer of cement in the world. In 2003, India produced 115 million metric tons (Mt) of cement, behind China (750 Mt), but ahead of the U.S. (93 Mt) and Japan (72 Mt). India’s cement industry – both installed capacity and actual production – has grown significantly over the past three decades, with production increasing at an average rate of 8.1% per year between 1981 and 2003. 2.2. Environmental Impacts of Cement production
Producing one tonne of cement requires about 2 tonnes of raw materials (shale and limestone) and releases approximately 1 tonne of CO2,...
References: 1. Annie J Peter, M. Neelamegam, J. K. Dattatreya, N. P. Rajamane and S. Gopalakrishnan, [Feb,1998], Utilisation of Fly ash as Cement Replacement Material to Produce High Performance Concrete, Proceeding of the National Seminar on Fly ash Utilisation for Metallurgical Laboratory, Jamshedpur, India.
2. BIS, Handbook on Concrete Mixes (Based on Indian Standards), Bureau of Indian Standards (BIS) Value Added Products, New Delhi.
3. Gopalakrishnan, S., Rajamane, N. P., Dattatreya, J. K., Neelamegam, M, and Annie Peter, J, [May, 2001], Effect of partial replacement of cement with fly ash on the strength and durability of HPC, The Indian Concrete Journal.
4. N. P. Rajamane, Scientist, Making Concrete 'Green ' Through Use of Fly Ash, Concrete Composites Laboratory Structural Engineering Research Centre, CSIR,Chennai.
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