The Effect of Utilising Coal Ash as Substitutes for Cement and Sand on Compressive Strength and Water Permeability of Concrete

Abstract The extensive use of concrete in construction significantly impacts the environment, primarily due to the extraction of natural sand and the high CO 2 emissions associated with its production. To mitigate these effects, sustainable concrete alternatives involve replacing cement with fly ash (FA) and sand with coal bottom ash (CBA). This study aims to evaluate the compressive strength and permeability of concrete mixtures incorporating FA and CBA. Six series of mixtures were designed, including a control series and mixtures with 10% FA and varying CBA substitutions of 10%, 20%, 30%, and 40%. The physical properties of the materials, such as specific gravity and water absorption, were assessed and utilized to formulate six mixture series. The control specimen was targeted to achieve a compressive strength of 60 MPa at 28 days. These mixtures were rigorously tested for water permeability and compressive strength at 7 and 28 days. The compression tests employed 100 x 100 x 100 mm specimens, while water permeability was assessed using 150 x 150 x 150 mm specimens. The results indicated a strong correlation between compressive strength and permeability (R 2 > 0.85). The optimal substitution levels were found to be 10% FA and 30% CBA, which enhanced the strength and permeability of concrete, making it suitable for construction applications.