Assessing the performance and sustainability of ecological mortar with municipal solid waste incineration fly ash solidified by sulphoaluminate cement

Abstract

Municipal Solid Waste Incineration Fly Ash (MSWI-FA) contains heavy metals, dioxins, and hazardous substances, making it a hazardous waste. The application of solidification/stabilization (S/S) treatment using chelating agents is widespread due to its high efficiency. However, this treatment is associated with high solidification costs. In this study, an attempt was made to solidify MSWI-FA using sulphoaluminate cement (SAC). Firstly, the effects of varying substitution rates of MSWI-FA on the workability, mechanical properties, durability and heat of hydration of ecological cement mortar (EM) were investigated. Secondly, the microstructure of the EM was investigated in order to ascertain the mechanism of solidification of the MSWI-FA via the SAC. Finally, the economic and environmental benefits of MSWI-FA as an alternative to SAC for the production of EM were evaluated using the material sustainability index. Results show that adding MSWI-FA decreases EM’s workability and mechanical properties, with compressive and flexural strength reductions between 6.87 % and 26.16 % and 5.74–36.74 %, respectively. Durability also declines, evidenced by increased drying shrinkage and chloride migration by 26.79–46.41 % and 11.05–48.19 %, respectively. A slower hydration rate reduces the total heat of hydration by 1.82–7.22 %, indicating lower cement hydration. The porosity and pore size increase, deteriorating the pore structure. However, SAC effectively solidifies heavy metals, with leaching rates for lead and zinc significantly below national standards. A 15 % substitution rate of MSWI-FA reduces energy consumption, carbon emissions, and production costs by 14.90 %, 14.63 %, and 4.03 %, respectively, demonstrating notable economic and environmental advantages.