The performance and microstructure of alkali-activated artificial aggregates prepared from municipal solid waste incineration bottom ash

In order to reduce the negative environmental impact of municipal domestic waste incineration bottom ash (MSWIBA), it is converted into lightweight aggregates by cold bonding technology. To enhance the utilization of waste materials, minimize cement consumption, and fabricate artificial aggregates with superior comprehensive performance, we designed and synthesized alkali-activated aggregates (AAAs) in this study. This study used MSWIBA and ground granulated blast furnace slag (GGBFS) as precursors for alkali-activated aggregates (AAAs), activated by a mixture of sodium hydroxide solutions and sodium silicate. The physical and mechanical properties of AAAs, including water absorption, apparent density, crushing strength and carbon-resistance, were investigated at different NaOH concentrations. In addition, the microstructure, mineral composition, aggregation, porosity and heavy metal leaching behavior of AAAs were analyzed by SEM, XRD, FTIR, TGA, MIP and ICP techniques. All AAAs exhibited a consistent particle size distribution, characterized by apparent densities spanning the range of 1633-1940 kg/m3. The leaching levels of heavy metals align with the standards established by Chinese regulations. Among the different activator concentrations tested, aggregate (M4) displayed superior single-particle crushing strength (3.90 MPa) and better carbonization resistance. It also used a lower concentration of NaOH, which enabled more cost-effective and eco-friendly production. Overall, the findings suggest that MSWIBA can be a viable precursor for producing sustainable lightweight concrete, with 4 M NaOH being the optimal activator concentration for achieving the best performance.

Automated summary

The municipal domestic waste incineration bottom ash (MSWIBA) is transformed into lightweight aggregates by cold bonding technology to reduce its negative environmental impact. Alkali-activated aggregates (AAAs) are designed and synthesized using MSWIBA and ground granulated blast furnace slag (GGBFS) as precursors, activated by a mixture of sodium hydroxide solutions and sodium silicate. The physical and mechanical properties, as well as the microstructure and heavy metal leaching behavior, of the AAAs are investigated. The findings suggest that MSWIBA can be a potential precursor for producing sustainable lightweight concrete, with 4 M NaOH being the optimal activator concentration for achieving the best performance.