Use of pretreatment to prevent expansion and foaming in high-performance MSWI bottom ash alkali-activated mortars

Abstract

This study has investigated the impact of foaming and expansion of municipal solid waste incinerator (MSWI) bottom ash (BA) during alkali reaction. Furthermore, the activity enhancement of the BA has been investigated. Based on the microanalytic appearance and compressive strength of the samples, the results show that the reaction between the metallic aluminium in the BA and alkali in the activator, which produced large quantities of hydrogen, is the primary cause for both foaming and expansion. The residual organic matter and unburnt substances in the BA are the main factors that affect the activity. However, the alkali defoaming and calcination-melting pretreatments completely prevented the expansion and calcining further improved the BA activity. The alkali activated materials prepared with the BA calcined at 700 °C, granulated blast furnace slag, and slaked lime followed by alkali defoaming pretreatment produced the best mechanical properties.