Determining Optimum Coal Bottom Ash/Slag Content for Sustainable Concrete Infrastructure

Concrete usage is increasing rapidly; subsequently, the industry’s carbon footprint is increasing and impacting the environment significantly. Large amounts of fine and coarse aggregate, including cement, are needed to fulfill the increased demand, leading to increased natural aggregate usage. Therefore, finding a fine aggregate replacement in concrete is essential. Coal bottom ash (CBA) and coal boiler slag (CBS), byproducts of coal-burning power plants with pozzolanic properties, can replace fine aggregate in concrete to reduce global natural material depletion, health hazards, and technical and economic problems associated with power plants’ solid waste. This study was conducted to determine the optimum fine aggregate replacement amount of CBA and CBS in concrete while improving concrete performance. The optimum CBA and CBS content is 50%, which reduces fine aggregate usage in a concrete mix by 50% while maintaining equivalent or better concrete strength than the control. The optimum CBA content has a unit weight lower than the control for all mixes tested in this study, which makes the CBA mix lightweight concrete. The optimum CBA concrete has 15%, 43%, and 42% higher compressive strength than the control after 7 days, 28 days, and 56 days of curing, respectively. On the other hand, the optimum CBS concrete has 12%,16%, and 16% increased compressive strength than the control after 7, 28, and 56 days of curing, respectively. The compressive strength of optimum CBA concrete was higher than the optimum CBS, indicating that CBA concrete yields higher compressive strength than CBS, possibly due to the difference in physical properties, water absorption capacity, and bulk density. Nanoclay increased CBA concrete compressive strength at an early stage and increased the optimum content to 80% CBA. Therefore, using CBA and CBS can significantly reduce natural material usage and environmental harm by reducing CBA waste disposal and improving concrete performance.