Working performance and microscopic mechanistic analyses of municipal solid waste incineration (MSWI) fly ash-based self-foaming filling materials

Abstract

To solve the problems of MSWI fly ash with no place stacking and the lack of filling materials in goaf, a scheme using MSWI fly ash for goaf filling is proposed. Using MSWI fly ash and slag as the main raw materials, geopolymer foaming materials with different proportions were prepared after alkali excitation to meet the differential filling requirements of goafs with different depths. The effects of curing temperature, activator dosage and MSWI fly ash content on the indexes of filling materials were investigated. The results showed that when the curing temperature was increased from 20 °C to 40 °C, the 28 d compressive strength of the material increased by approximately 31.9 %. The increase in curing temperature significantly improved the degree of polymerization and heavy metal curing rate of the material, resulting in more polymerization products in the system and promoting the conversion of calcium silicate hydrate (CSH) to calcium aluminosilicate hydrate (C-ASH) with a higher degree of polymerization. The pore structure of the material was mainly affected by the amount of activator used and the MSWI fly ash content. The higher the MSWI fly ash content was, the less round the pores and the more complex the spatial distribution. Scanning electron microscopy (SEM) showed that increasing the curing temperature and activator dosage made the raw material particles more compact and improved the integrity of the polymeric materials. Finally, three proportions involving an activator dosage of 20 % and a fly ash content of 40 %, an activator dosage of 15 % and a fly ash content of 40 % and an activator dosage of 10 % and a fly ash content of 60 % were selected for goaf filling at 20 °C, 30 °C and 40 °C, respectively.