Use of Coal Fly Ash or Glass Pozzolan Addition as a Mitigation Tool for Alkali-Silica Reactivity in Cement Mortars Amended with Recycled Municipal Solid Waste Incinerator Bottom Ash

Abstract

Municipal solid waste incinerator bottom ash was evaluated for its alkali aggregate reactivity in cement mortars. Subsequently, two wastes were evaluated as supplementary cementitious materials for their efficacy in mitigating expansive alkali-silica reactions in cement mortars amended with bottom ash. Three bottom ashes were incorporated into mortar bars as 15, 30 and 50% replacements of non-reactive sand. Control MSWI amended mortars were compared to those containing coal fly ash and glass pozzolan (synthetic glass). Dimensional expansion of the mortars was measured over 14 days to quantify the extent to which the recycled coal fly ash and glass pozzolan mitigated the alkali reactivity of the ash-amended mortar specimens. Average expansions of the ash-amended mortars ranged from 0.10 to 0.40%, suggesting that ash components reacted expansively in an alkaline environment. Microscopic analysis was used to complement the data and confirm the presence of silica-rich gel within glass fragments of the ash, as well as cracking of the aggregates. Supplementary cementitious materials (class F coal fly ash, glass pozzolan) mitigated expansion of the mortars by 90% on average, likely through consumption of the alkalis in the paste pore water.