Activation of municipal solid waste incineration ashes for green concrete

Abstract

Due to the variable characteristics of municipal solid waste incineration (MSWI) ashes and the lack of coherent standards and regulations, a majority of MSWI ashes is landfilled currently. It is an urgent issue that the significant amount of residue MSWI ashes need to be better handled and reused as a renewable source. MSWI ashes have great potential to be utilized as a cementitious replacement material in concrete mixing, which is beneficial for both promoting MSWI ash reuse and reducing cement consumption. However, there are major challenges associated with MSWI ash reuse, including the presence of lack of efficient approach to restore the reactivity of MSWI ashes as a binding agent, because such ashes are usually low in reactivity or even inert. This study aims to develop an effective and reliable activation method to enable the pozzolanic and hydraulic properties of MSWI ashes. A novel activation methodology by means of physiochemical treatments, including particle size reduction and high pH activator was proposed to increase the reactivity of such bottom ashes. A rapid test method, namely solution test, was developed to test the potential reactivity after the activation. Thermogravimetric analysis (TGA) and ion chromatography (IC) were employed to evaluate the degree of reactivity. The results showed that the physicochemical treatment can indeed increase the reactivity of MSWI ashes. Compared to the existing test protocols using normal activator the new solution test can more effectively examine the latent pozzolanic activities of MSWI ashes. The successful application of the proposed activation methodology together with the developed solution test could turn those “inert or low reactivity” to-be-landfilled ashes into an active binding agent as a cement replacement material, which would contribute greatly to recycle and reuse of waste materials and reduce CO2 emission.