Flyash is the by-product of the combustion of pulverized coal and is collected by mechanical and electrostatic separators from the fuel gases of power plants where coal is used as a fuel and the disposal of flyash is one of the major issues for environmentalists as dumping of flyash as a waste material may cause severe environmental problems/hazards. The use of high volume class F flyash as a partial replacement of cement in concrete decreased its mechanical properties, modulus of elasticity and abrasion resistance of the concrete. The utilization of flyash instead of dumping it as a waste material can be partly used on economic grounds as pozzolana for partial replacement of cement and partly because of its beneficial effects such as lower water demand for similar workability, reduced bleeding, and lower evolution of heat and has been used particularly in mass concrete applications and large volume placement to control expansion due to heat of hydration and also helps in reducing cracking at early ages.
High volume Fly Ash Concrete
80% of Class F flyash can be suitably used as cement replacement in concrete by using a rational mixture proportions. The compressive and flexural strength of the high volume flyash concrete mixtures demonstrated continuous and significant improvement at late ages of 91 and 365 days.
Class F flyash may replace 50% of the portland cement and could result in improving resistance to chloride initiated corrosion but such replacement however may significantly reduce the values of the mechanical properties.
High-performance concrete with moderate and high strength and low temperature rise could be produced using high volumes of flyash as cement replacement resulting in a reduction in the maximum temperature rise and also increasing the replacement level of flyash caused lower temperature rise in concrete.