Energy is the major backbone of modern world and the electric power generated from thermal power stations is a major source of energy, in the form of electricity. In India, more than 70% of electricity generated is by the combustion of fossil fuels, out of which nearly 61% is produced by coal-fired thermal power plants. This results in the production of roughly 100 ton of ash. Most of these ashes disposed off either dry, or wet to an open area available near the plant or by grounding both the fly ash and bottom ash and mixing it with water and pumping into artificial lagoon or dumping yards or in the mines itself. This leads to the pollution of water bodies and loss of productive land.
The continuous reduction of natural resources and the environmental hazards posed by the disposal of coal ash has reached alarming proportion such that the use of coal ash in concrete manufacture is a necessity than a desire. The use of coal ash in normal strength concrete is a new dimension in concrete mix design and if applied on large scale would revolutionize the construction industry, by economizing the construction cost and decreasing the ash content. This paper presents the experimental investigation carried out to study the effect of use of fly ash as a replacement of cement and bottom ash as a replacement of fine aggregates. Although, fly ash is being generally used as replacement of cement concrete, the study on the use of bottom ash (the coarser material, which falls into furnace bottom in modern large thermal power plants and constitute about 20% of total ash content of the coal fed in the boilers) has been very limited.
The use of by-products or wastes from coal-fired thermoelectric plants has evolved into a reality in the production of concrete, resulting in good mechanical performance, good compatibility with raw materials in the concrete and durability [1â€"3].
The most important properties of BA are the size and shape of the particles and the porosity. Such properties depend on the burning efficiency, the method in which the BA is obtained and the type of combustion. When very small molten and well vitrified particles around 30 μm are formed, this satisfies the basic requirements of a fine aggregate for concrete and mortar, even if grain size distribution varies. There is also pozzolanic potential, although this is low due to the grain size [4]. Bottom ash (BA) has also been targeted in some publications for its use in concrete and mortar [4â€"8].
The compressive strength data observed at various ages (1, 3 and 7 days) are shown in Table 4. At age of 1 day, control mixture showed the highest value of compressive strength of the mixes tested and all the other mixes shows lower value of the compressive strength at the age of 1 day. The poorest performance among the mixture is the one with high content of bottom ash, which did not contribute sufficient strength at this very early age because of its relatively low reactivity. At the age of 3 days, there was continuous improvement in the performance of the mixtures. When curing extended to 7 days, a steady increase in the performance of the mixtures was noticed. Most of the compressive strength values of the cement mixes are satisfactory when compared to the control mix. This was probably due to large pozzolanic contribution of the fly ash and bottom ash [10].
