Mechanical Properties of High Volume Fly Ash(HVFA) Concrete Subjected to Evaluated Temperatuers up to 120 Deg Celcius.

Abstract

Waste disposal is one of the major problems being faced by all the nations across the globe. Fly ash is an industrial by-product, generated from combustion of coal in the thermal power plants. The increasing scarcity of raw materials and an urgent need to protect the environment against pollution has accentuated the significance of developing new building materials based on industrial waste generated from coal fired thermal power station and is creating unmanageable disposal problems due to its potential to pollute the environment. Pozzolanic concretes are used extensively throughout the world where oil, gas, nuclear and power industries are among the major users. The applications of such concretes are increasing day by day due to their superior structural performance, environmental friendliness, and energy conserving implications. Apart from the usual risk of fire, these concretes are exposed to high temperatures for considerable periods of time in the above-mentioned industries. Although concrete is generally believed to be an excellent fireproofing material, but there is extensive damage or even catastrophic failure at high temperatures. At high temperatures, chemical transformation of the gel weakened the matrix bonding, which brought about a loss of strength of fly ash concrete. Fly ash is used as a mineral addition in concrete to improve its strength and durability characteristics. Fly ash can be used either as an admixture or as a partial replacement of cement or as a partial replacement of fine aggregates or total replacement of fine aggregate and as supplementary addition to achieve different properties of concrete. In the present study, the compressive strength, split tensile strength and modulus of elasticity of fly ash concrete at elevated temperature up to 120˚C with mix proportions of 1:1.45:2.2:1.103 with a water cement ratio of 0.5 by weight was determined. Cement was replaced with three percentages of fly ash. The percentages of replacements were 30, 40 and 50 % by weight of cement. Tests were performed for compressive strength, split tensile strength and modulus of elasticity. Compressive strength, split tensile strength and modulus of elasticity were performed at room temperature, 80˚C, 100˚C, and 120˚C for all types of fly ash concrete at different curing periods (28 and 56 days). Reference concrete without fly ash has also been used. Test results showed that the compressive strength, split tensile strength and modulus of elasticity of concrete having cement replacement up to 30% was comparable to the reference concrete without fly ash. Compressive strength, split tensile strength and modulus of elasticity of concrete mixtures with 30%, 40% and 50 % of fly ash as cement replacement was lower than the control mixture at all ages and that the strength of all mixtures continued to increase with the age. With the increase in temperature, compressive strength of concrete mixes with 30%, 40% and 50 % of fly ash as cement replacement decreases by 11.4%, 30.1%, 28.9%, and 27.5% at 120˚C when compared to room temperature.