Evaluation of alkali-silica reactivity behavior and mitigation in waste-to-energy bottom ash for sustainable aggregate use in concrete

Abstract

The beneficial use of waste-to-energy (WTE) bottom ash (BA) as a recycled aggregate in concrete enhances sustainability by reducing reliance on virgin aggregates and diverting industrial waste from landfills. One of the most limiting challenges for this reuse opportunity includes the potential for alkali-silica reactivity (ASR) caused by elevated silica inherent to WTE BA glass and ceramic particles interacting with hydroxides introduced by cement. Two WTE BA-derived aggregates were investigated, and in both cases the test material demonstrated elevated ASR-induced expansion compared to control specimens. Beneficiation of the WTE BA through advanced metals recovery reduced ferrous and nonferrous metals and metallic slag compared to the unprocessed BA. Total element concentration between the two BA-amended aggregates demonstrated a decrease in trace elements such as Al, As, Pb, and Sb. Despite these techniques, specimens containing the processed BA still exhibited elevated ASR compared to control specimens. The addition of coal fly ash reduced ASR severity, although reactivity remained present. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) identified siliceous particles, including glass, ceramics, and slag, as primary contributors to ASR. This suggests that methods for targeted removal of reactive particles of these materials would be useful in reducing ASR and increasing WTE BA recycling.