An investigation on optimizing the carbonation resistance of coal bottom ash concrete with its carbon footprints and eco-costs

Abstract

Energy from coal-fed thermal power plants is provided at the cost of the generation of coal ash. Coal bottom ash (CBA) is an ash generated in coal-fed power plants which is landfilled. Existing literature reports the potential of CBA as a replacement for Portland cement (PC) and natural fine aggregates (NFA) in concrete. Carbonation is an important durability parameter of concrete having fatal consequences at later ages if not estimated and controlled as it leads to corrosion in reinforcement. In the present study, experimental, microstructural, and statistical analysis along with life cycle assessment was performed to investigate the combined effect of two-hour grinded CBA (GCBA) as PC (10-30%) and raw CBA as NFA replacement (0-50%) on compressive strength and carbonation resistance. Accelerated carbonation tests were performed at an exposure of four weeks after 28 and 90 days of curing. Among CBA-based concrete mixes, concrete with 20% GCBA and 25% CBA (G20C25) reported higher compressive strength and carbonation depth owing to pozzolanic reactivity and filler effect of fine CBA particles. However, G20C25 resulted in comparable performance in comparison with the control mix in terms of strength and carbonation resistance. The findings of X-ray diffraction spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy also validate the trends. The mathematical models derived for the carbonation resistance and strength were well-fitted. Multi-objective optimization recommended 21.5% GCBA and 29.8% CBA as the optimum amount that resulted in 20.08% and 19.40% lower carbon footprints and eco-costs compared to control mix.