Permeation, Toxicity, and Sustainability Assessment of Thermal Coal-Residue Concrete

The permeation properties and leachability of waste-based sustainable concrete are essential for its strength, durability, and resistance to harsh environments. This study explored the combined effects of using coal bottom ash (CBA) as a substitute for both portland cement (PC) and natural fine aggregate (NFA) in concrete. CBA, a dense ash byproduct from thermal power plants, was ground (GCBA) for 2, 6, and 10 h to replace 10%–30% of PC, while raw CBA replaced 25% and 50% of NFA. The study assessed compressive strength and permeation properties, such as capillary suction, initial surface absorption, and water impermeability, after 28 and 90 days of curing. The toxicity characteristic leaching procedure (TCLP) was performed to evaluate the leaching behavior of both raw and ground CBA, as well as CBA-based concrete mixes. Additional tests, such as ultrasonic pulse velocity (UPV) and apparent electrical resistivity, were also conducted. Microstructural investigations comprising X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) supported the experimental results. The mix containing 20% GCBA ground for 6 h and 25% CBA (P6G20C25) showed the best performance, attributed to the pozzolanic reactivity of GCBA and the filler effect of fine CBA. Mathematical models and multiobjective optimization indicated that a grinding time of 6.72 h, with 21.98% GCBA and 27.24% CBA, resulted in a 17.68% reduction in carbon footprints and a 16.62% reduction in eco-costs compared to the control mix.