Effect of Low-Calcium Coal Bottom Ash as Fine Aggregate on Microstructure and Properties of Concrete

This study evaluates the strength and durability properties of concrete incorporating low-calcium coal bottom ash as partial or total replacement of fine aggregate. The test results indicate that at a fixed water-cement ratio (w/c), workability, 28-day compressive strength, splitting tensile strength, and pulse velocity through concrete decreased with the increase in coal bottom ash content. With age, the compressive strength of bottom ash concrete improved at a faster rate compared to that of a control concrete. Bottom ash concrete achieved compressive and splitting tensile strengths comparable to that of the control concrete at 180 days and 90 days, respectively. At 28 days and up to 75% sand replacement level, chloride ion penetration increased with increase in coal bottom ash content in concrete. However, with age, opposite results in respect of chloride ion penetration were observed Bottom ash concrete and the control concrete showed almost identical performance under external sulfate and acid attack. Microstructural analysis revealed that pozzolanic activity of coal bottom ash in concrete started after 28 days. X-ray diffraction spectrums indicate that the phase composition of powder concrete paste was not changed qualitatively; however, the change in phase proportions was observed on use of coal bottom ash in concrete. Bottom ash concrete displayed slightly lower resistance to abrasion as compared to control concrete.