Utilization of municipal solid waste incineration fly ash with coal fly ash/metakaolin for geopolymer composites preparation

The geopolymer technique is a promising method for the solidification/stabilization (S/S) treatment of municipal solid waste incineration fly ash (MSWIFA). To investigate the feasibility of resource utilization in MSWIFA by geopolymerization process, the macroscopic and microscopic properties of the coal fly ash/metakaolin-based geopolymer composites containing MSWIFA were studied. The leaching test was conducted to evaluate the S/ S effect of geopolymer. Results showed that CFA/MK-based geopolymer demonstrated effective stabilization of heavy metals in MSWIFA. The flowability of geopolymer composites increased with the MSWIFA content, where 40% replacement ratio of MSWIFA significantly improved the slump and consistency of geopolymer mortar by 86.3% and 80.4%. However, 40% content of MSWIFA reduced the compressive strength and splitting tensile strength of geopolymer composites by 80% and 62%. The strength development rate in early ages of geopolymer composites was accelerated by mixing less than 15% MSWIFA. Whereas, the strength development at 7-28 days was almost unaffected by MSWIFA. The addition of MSWIFA decreased the amount of sodium-(calcium) aluminosilicate hydrate and sodium aluminosilicate hydrate gels. Although the addition of MSWIFA refined the gel pores in geopolymer, the pore volume and porosity increased and the compactness of microstructure decreased with the increment of the MSWIFA content in geopolymer composites. Based on these results, it is feasible to realize resource utilization of MSWIFA using geopolymer composites with low content of MSWIFA (less than 15% was recommended in this study).