Chloride leaching and strength development of alkali-activated materials with municipal solid waste incineration fly ash, red mud and carbide slag.

Abstract

Using as an alkaline activator to produce alkali-activated materials (AAMs) for construction and buildings provides an economic strategy for the treatment of hazardous municipal solid waste incineration fly ash (MSWI FA). In this study, Al₂O₃-rich red mud (RM) and CaO-rich carbide slag (CS) were used to tackle the chloride leaching issue of AAMs with MSWI FA arising from the Cl in MSWI FA. The optimal content of RM and CS for achieving higher compressive strength and less chloride leaching was determined. FTIR, XRD and TGA were employed to reveal the variation in phase assemblage with the raw materials and carbonation treatment. The results showed that the system with 10 % CS, 20 %RM, 20 % MSWI FA and 50 % GGBS achieved the maximum compressive strength at 56 days (27.5 MPa) and the minimal water-soluble chloride concentration (3.5 %). RM provided alkalis to activate GGBS also Si and Al to generate additional gels; the calcium from CS facilitated the precipitation of Friedel's salt, thereby reducing the chloride leaching, but more CS than 10 % negatively impacted the compressive strength due to excessive alkalinity. Whilst an appropriate carbonation treatment densified the matrix, it increased the chloride leaching as a consequence of the replacement of Cl^- by CO₃^2- in the chloride binding phases. The results obtained offer technical assistance for better management of solid wastes.