ENVIRONMENTAL AND COMPRESSIVE STRENGTH EFFECTS OF COAL BOTTOM ASH AS PARTIAL SAND REPLACEMENT IN CONCRETE: A LEACHING ASSESSMENT STUDY

Abstract

One coal waste is coal bottom ash (CBA), which has an environmental impact due to its heavy metal content. This study reveals the dual role of CBA as a partial sand replacement in concrete through leaching ability analysis to assess mechanical performance and environmental safety. The concrete mixture was prepared by placing CBA at 0%, 30%, 40%, 50%, and 60%, and then a compressive strength test was carried out at the periods of 7 and 28 days. Using the Synthetic Precipitation Leaching Procedure and ICP-MS analysis, the leaching behavior was evaluated. The results showed that adding CBA up to 50% increased the 28-day compressive strength by 6.42% compared to the control concrete. In comparison, higher replacement (60%) caused a decrease in strength due to increased porosity and unburned carbon, which prevented hydration. Leaching tests showed that adding CBA reduced the mobility of Cr, Pb, Zn, and Cd in concrete by combining physical encapsulation in the cement matrix and chemical stabilization by forming calcium silicate hydrate (C–S–H) gel. The maximum reduction was observed at 50% CBA: Cr (27.9%), Pb (67.9%), Zn (1.5%), and Cd (10.2%) compared to control concrete. However, using CBA in concrete needs to be controlled because the concentrations of Cr and Pb in some mixtures exceed the USEPA threshold, indicating potential risks for soil and groundwater. This study is beneficial for sustainable construction.