Effect of coal bottom ash on strength and durability properties of concrete

Abstract

In India, about 35 million tons of coal bottom ash is produced annually. It is dumped on land adjoining sites of thermal power plants and is becoming environmental hazard to surrounding community. The productive use of coal bottom ash is the best way to alleviate the problems associated with its disposal. The present research work has been carried out to evaluate the feasibility of utilization of coal bottom ash as fine aggregate in concrete. Concrete A made with sands having fineness modulus of 1.97 and concrete B made with sands having fineness modulus of 2.58 were designed to achieve 28-day compressive strength of 38 and 34 N/mm2, respectively. In both concretes, river sand was replaced with coal bottom ash at 20, 30, 40, 50, 75 and 100% levels. Properties such as workability, bleeding and air content of fresh concrete were evaluated. Tests for compressive strength, splitting tensile strength, modulus of elasticity, water absorption and water absorption, pulse velocity, chloride permeability, abrasion resistance, sulphate resistance, acid resistance and drying shrinkage were performed up to the age of 365 days. Test results show that workability and water loss through bleeding decreased whereas entrained air content increased on inclusion of coal bottom ash as replacement of sand in both concretes tested. For concrete A and B , unit density decreased almost linearly with increase in coal bottom ash content. At early curing age of 7 days, bottom ash concrete mixtures achieved lower compressive strength. 28-day compressive strength of bottom ash concrete mixtures varied between 35.0 and 37.5 N/mm2 for concrete A and between 26.7 and 32.2 N/mm2 for concrete B as compared to 38.20 and 34.0 N/mm2, respectively, of control concrete mixtures. With age, compressive strength of bottom ash concrete mixtures increased at a faster rate than that of control concrete mixtures.