03-05-2013, 02:28 PM
Effect of fine aggregate replacement with fly ash on the mechanical properties of concrete
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ABSTRACT
The utility of flyash as partial replacement in concrete mixes is on rise these days. Flyash is a waste product which is generated in thermal power stations. The quantity of fly ash produced from thermal power plants in India is approximately 105 million tons each year, and its percentage utilization is less than 13%. Majority of fly ash produced is of Class F type. The use of these materials would reduce the disposal problems now faced by the thermal power stations and industrial plants. During the last few years, some cement companies have started using fly ash in manufacturing cement, known as 'Pozzolana Portland cement', but the overall percentage utilization remains very low, and most of the fly ash is dumped at landfills.
Fly ash is generally used as replacement of cement, as an admixture in concrete, and in manufacturing of cement. Whereas concrete containing fly ash as partial replacement of cement poses problems of delayed early strength development, concrete containing fly ash as partial replacement of fine aggregate will have no delayed early strength development, but rather will enhance its strength on long-term basis. In this investigation flyash is used as sand replacement material. The material mix of proportion 1:1.45:2.46:0.5. Each category comprises of various percentages of sand replacement material in increasing order i.e. 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, and 55%. The workability is maintained constant for all mixes. Strength characteristics such as compressive strength flexural strength split tensile strength of concrete mixes are found out for seven and twenty eight days curing period and results are analyzed
INTRODUCTION
The demand for cement as well as other primary building material is increasing in the country because of growth in economy, population and living standards. Cement production in the country is estimated to be around 90 million tonnes per annum and is expected to be growing at 10% per annum (1)
Cement concrete has established itself as the most preferred material of construction owing to its versatility, ease in production and use (1). However, three aspects are gaining emphasis in the use of concrete. The first one is the durability aspect. The importance of durability is amply reflected in the revised code of practice on concrete IS 456-2000. The second aspect is the economy in construction by improved design and cost reduction in cost of materials. The third aspect relates to energy conservation and environment protection. These three factors can be uniquely addressed by the use of fly ash in concrete.
The present production of fly ash in our country is around 100 million tonnes per annum of which about 20% is being gainfully utilized. The utilization of fly ash in concrete making, though, is negligible. Concrete owes its unique position as the structural material to the fact, that it is economically highly resistant to fire, wind, water and earthquakes. The demand is likely to increase in the future to match the growing population, housing, transportation and other amenities. However, on many occasions individual materials as such may not serve the specific purpose. Concrete can be called as a composite material. For reducing the cost of concrete, greater use of pozzolonic materials like flyash and blast furnace slag was suggested. The use of these materials as the substitute material in concrete would reduce the disposal problems now faced by thermal power plants and industrial plants and at the same time achieving the required strength of concrete.
CONCLUSIONS
1. It has been observed that as the percentage of flyash increases the compressive strength increases initially, on further increase in its percentage reduces its compressive strength. It can be seen that when sand is partially replaced by flyash by 52% (52P) the compressive strength reaches its maximum for both 7 & 28 days curing period. The maximum compressive strength of flyash concrete (52P) is increased by 71.58% and 45.32% when compared to plain concrete (P) for 7 and 28 days curing period.
2. It has been observed that as the percentage of flyash increases the tensile strength increases initially, on further increase in its percentage reduces its tensile strength.
It can be seen that when sand is partially replaced by flyash by 52% (52P) the tensile strength reaches its maximum for both 7 and 28 days curing period. The maximum tensile strength of flyash concrete (52P) is increased by 57.4% and 13.23%, when compared to plain concrete (P) for 7 & 28 days curing period.
3. It has been observed that as the percentage of flyash increases the flexural strength increases initially, on further increase in its percentage reduces its flexural strength. It can be seen that when sand is partially replaced by flyash by 52% (52P) the flexural strength reaches its maximum for both 7 and 28 days curing period. The maximum flexural strength of flyash concrete (52P) is increased by 34.61% and 35.81% when compared to plain concrete (P) for 7 & 28 days curing period.