Study on preparing sustainable limestone calcined clay cement (LC3) through CO2-active treatment of municipal solid waste incineration fly ash (IFA)

Abstract

Municipal solid waste incineration fly ash (IFA) is theoretically more suitable for forming a composite cementitious system with cement and calcined clay compared to inert limestone due to its pozzolanic activity. In addition, IFA contains high levels of alkaline calcium compounds that have the potential for carbonation. The study examined the improvement of CaCO3 content within IFA facilitated by CO2-active (CIFA), replacing limestone in limestone calcined clay cement (LC3), and creating sustainable cementitious materials. The hydration behavior, heavy metal morphologies and mechanical properties of (C)FC3 were studied. The research indicates that introducing IFA adversely affects the initial hydration process of the system, but this inhibition is alleviated by using CIFA. This is facilitated by the reduction in sulfate dissolution rate attributed to the formation of carbonate shells. The incorporation of IFA into the system leads to the effective utilization of Ca(OH)2, thereby enhancing the pozzolanic reaction of the calcined clay. Consequently, (C)FC3 show higher compressive strength than LC3 at 56 d, with L15, F15 and CF15 achieving 29.9 MPa, 39.6 MPa and 46.8 MPa, respectively. While there is an increase in the exchangeable and acid-soluble states in CFC3, the elevation of oxidizable and residual states contributes to a reduced potential for total leaching in harsh environments. The excellent mechanical properties and environmental stability confirm the feasibility of using (C)IFA for LC3.