Effect of Alkali Content on the High-Temperature Behavior of Alkali-Activated Slag Paste Containing MSWI Bottom Ash

Abstract

The accumulation of municipal solid waste incineration bottom ash (MSWI-BA) not only occupies land, but also leads to severe environmental pollution. In order to improve the utilization of MSWI-BA and reduce carbon emissions, the effect of alkali content on alkali-activated slag (AAS) paste containing 12% MSWI-BA under high-temperature exposure was studied. The alkali contents, i.e., the mass of Na2O in the water glass, were 2%–6% of the total mass of the precursors. The weight loss, thermal shrinkage, and strength of AAS were investigated. The results show that at the same heat treatment temperature, as the alkali content increases, the flexural and compressive strengths of AAS increase and then decrease, reaching the maximum at AAS with 4% alkali content (NS4). As the alkali content increases from 2% to 4%, the higher OH− concentration reduces the Ca dissolution of portlandite in MSWI-BA, resulting in a lower increase in Ca concentration than Si concentration. This leads to a decrease in Ca/Si and an increase in Al/Si of C─ A─ S─ H, which is beneficial for improving the structural stability of C─ S─ H after high temperature. When the alkaline content increases from 4% to 6%, excessive matrix shrinkage leads to an increase in microcracks. It was found that NS4 has the best high-temperature resistance and has good application prospects in engineering.