Valorization of bottom ash in concrete: serviceability, microstructural and sustainability characterization

The present study investigated the synergistic influence of bottom ash as a Portland cement (PC) and natural fine aggregate (NFA) replacement in concrete. Coal bottom ash (CBA) is a heavy ash that settles at bottom of combustion chamber of a thermal power plant and was grinded (GCBA) for two hours prior to replacing 10-30% PC whereas CBA was used in raw form to replace 25% and 50% NFA. The mechanical properties along with durability properties (accelerated carbonation and chloride penetration) were studied after 28 day and 90 days curing. Non-destructive tests were also performed to check the quality of CBA based concrete. Microstructural characterization was conducted using various techniques like XRD, SEM and FTIR. The concrete with 20% GCBA and 25% CBA (G20C25) reported best performance in terms of parameters studied owing to pozzolanic reactivity of GCBA and filler effect of fine CBA. The microstructural investigations also validated the findings and trends observed of experimental results. Well fitted mathematical models were derived and optimisation was carried out using desirability function approach. Multi-objective optimization recommended 21.80% GCBA and 24.17% CBA as the optimum amount resulting in significant reduction of 19.19% and 18.19% in carbon footprints and eco-costs compared to control mix.