Improving the high temperature resistance of alkali-activated slag paste using municipal solid waste incineration bottom ash

In order to further enhance the high temperature resistance of alkali-activated slag (AAS) and promote the consumption of municipal solid waste incineration bottom ash (MSWI-BA), 0–12 wt% of slag was replaced by MSWI-BA, and the influence of MSWI-BA content on the high temperature resistance of AAS paste was studied. The performance of AAS paste containing MSWI-BA after high temperature was investigated, including weight loss, thermal shrinkage and strength. Meanwhile, the microstructure of AAS was investigated to unravel the high temperature resistance mechanism. Results show that, for the same temperature, the flexural and compressive strengths of AAS rise initially, and then fall as MSWI-BA content rises, reaching their highest value in AAS with 6% MSWI-BA. The flexural and compressive strength of AAS with 6% MSWI-BA at 400 °C are 31.3% and 17.9% higher than that of AAS without MSWI-BA, respectively. When MSWI-BA content is less than 6%, the presence of portlandite and hydrotalcite in MSWI-BA increases the alkali concentration and accelerates the hydration reaction, which promotes the formation of C-A-S-H gel with high degree of polymerization. Besides, the hydrogen generated by the reaction of elemental aluminum in MSWI-BA and OH− can improve the pores connectivity of matrix, and reduce the water vapor pressure and shrinkage, thus inhibiting matrix cracking. However, due to its low activity and porous characteristics, an excessive amount of MSWI-BA (>6%) leads to a decrease in the amount of C-A-S-H and a significant increase in porosity, thus reducing the strength of AAS.