The use of fly ashes from waste-to-energy processes as mineral CO2 sequesters and supplementary cementitious materials

This study explores the simultaneous application of fly ash (FA) generated from the thermal treatment of municipal solid waste as a CO2 sequester through aqueous mineral carbonation and as a supplementary cementitious material (SCM) for the development of green construction materials. Two types of FAs are tested, namely an incineration fly ash (IFA) collected from electrostatic precipitator of an incineration plant and a gasification fly ash (GFA) collected from air pollution control unit of a high temperature slagging gasification waste-to energy (WTE) plant. Ground waste glass (GWG) is used as a tertiary SCM. GFA demonstrates favorable sequestration capacity (87.5 mg/g) and high carbonation degree (74.1 %) while the IFA is found to be inactive during carbonation (3.1 mg/g, 4.6 %). Mortars blended with the wastes have shown delay in the cement hydration but eventually achieve compressive strength comparable to the control specimen. The mixing of GWG and GFA synergistically improves the performance of mortars which highlights the importance of strategic coupling of different waste streams. Most of the hazardous heavy metals, chloride and sulfate in FAs were stabilized in the mortars suggesting the potential for safe re-utilization of carbonated FAs as sustainable SCMs to concurrently close the waste loop and combat climate change.