Use of municipal solid waste incineration bottom ash as a supplementary cementitious material in dry-cast concrete

Abstract

This study evaluates the feasibility of partially replacing Portland cement in concrete with bottom ash (BA) from municipal solid waste incineration (MSWI). The challenge with this ash lies in its susceptibility to react expansively in alkaline conditions, leading to cracking when used in conventional high-slump concrete. This expansive behavior was confirmed to be the result of the dissolution of the ash’s aluminum metal content and consequent formation of hydrogen gas. The aim of this study was to explore the suitability of BA as a cementitious additive in zero-slump dry-cast concrete instead. The premise was that dry-cast could better diffuse the generated gas and avoid internal pressure build-up. Results from isothermal calorimetry and thermal gravimetric analysis (TGA) clearly correlate enhancements in early-age cement hydration and pozzolanic reactivity. Scanning electron microscope (SEM) images revealed voids channels and larger aggregation formation in the BA applied concrete paste. Dry-cast concrete containing 20% BA replacement of cement exhibited higher strengths than ordinary Portland cement (OPC) reference samples at every test age up to 90 days, with the ultimate strength of BA concrete being 18% higher than that of OPC concrete. The addition of BA also improved resistance to freeze–thaw damage. The study found that MSWI-BA can impart enhancements to dry-cast concrete, qualifying it as a potentially suitable supplementary cementitious material. Use of this otherwise landfilled ash as raw feedstock in concrete-making demonstrates a greener approach to building – scoring favorably in environmental performance for being relevant to resource conservation, landfill diversion, and waste-recycling.