Analysis of chloride resistance in light weight concrete made from fly ash and bottom Ash

The combustion process of coal in a steam power plant produces about 5% of fly ash and bottom ash (FA-BA) waste, which is a solid waste material that cannot be burned and can cause environmental pollution. This research aimed to modify lightweight concrete by using fly ash waste as a substitute for Portland cement and bottom ash waste as a substitute for fine aggregate. The lightweight concrete was tested for resistance to hydrochloric acid (HCl) with a potential of hydrogen (pH) range of 6-8 under three test conditions. The percentage of fly ash waste used as a substitute for cement ranged from 10% to 40% of the total weight of cement, while the percentage of bottom ash waste used as a substitute for fine aggregate ranged from 30% to 50% of the total weight of fine aggregate. The test results showed that the lightweight concrete composition with the lightest specific gravity was found in the FL40BO50 mixture with a density of 1.70 gr/cm3 and a minimum compressive strength of 15.92 MPa. However, the most optimal specific gravity was found in the FL20BO30 mixture. The lightweight concrete with a specific gravity of 1.84 gr/cm3 and the most optimal compressive strength of 25.17 MPa was obtained. In the test results for HCl resistance, the lightweight concrete with the FL20BO30 mixture experienced the minimum mass loss, while the FL40BO50 mixture experienced the maximum decrease in mass. Under testing conditions 1, the lightweight concrete experienced a mass decrease ranging from 0.36% to 1.61% of the initial mass. Under testing conditions 2, the lightweight concrete decreased in mass by 0.65% to 3.50% of the initial mass. Under testing condition 3, the lightweight concrete experienced a mass decrease ranging from 1.03% to 4.81% of the initial mass. The decrease in mass was due to the formation of microcracks in the lightweight concrete caused by the chloride content in the HCl solution, which attacked the bonding mechanism in the lightweight concrete.