Strength properties and micro-structural properties of concrete containing coal bottom ash as partial replacement of fine aggregate

• Utilization of coal bottom ash (CBA) as fine aggregate in concrete.
• River sand replaced with 0%, 20%, 30%, 40%, 50%, 75% and 100% CBA.
• Relations between splitting-tensile and compressive strength presented.
• Relation between density and modulus of elasticity presented.

The coal fired thermal power plants are the main source of production of coal ash. The coal ash collected at the bottom of the furnace is called coal bottom ash (CBA). The objective of the present research work was to explore the possibility of utilization of coal bottom ash as partial replacement of fine aggregate (sand) in concrete. Experimental tests were performed to evaluate the properties of fresh and hardened concrete containing coal bottom ash. The properties such as unit weight, compressive strength, and splitting tensile strength, modulus of elasticity and microstructure of concrete incorporating coal bottom ash in partial or full replacement of river sand were examined and compared with those of conventional concrete. Water loss by bleeding and workability of fresh concrete after replacing river sand with coal bottom ash were also examined. The test results of this research work indicate that at fixed water cement ratio, workability and loss of water from bleeding decreased with the use of coal bottom ash as a replacement of river sand in concrete. Compressive strength of bottom ash concrete at the curing age of 28 days was not strongly affected. However, after 90 days of curing age, compressive strength of bottom ash concrete surpassed that of conventional concrete. Splitting tensile strength of concrete improved at all the curing ages. The modulus of elasticity decreased with the use of coal bottom ash at all the curing ages. SEM and XRD studies indicated that the C–S–H gel structure was slightly less monolithic than that of control concrete and total intensity of ettringite was not changed with the addition of coal bottom ash in concrete.