Utilization of municipal solid waste incineration fly ash to produce autoclaved and modified wall blocks

Municipal solid waste incineration fly ash (MSWI) as hazardous solid wastes, its growing generation has become a great burden to the society and thus its proper management is greatly necessary. In this work, MSWI and fly ash (FA) were used as raw materials to prepare solid wastes-based autoclaved wall blocks (SW-AWBs). To further improve the durability of SW-AWBs, three admixtures (NaCl, NaNO3 and NaOH) were separately incorporated and their effects on drying shrinkage, frost resistance, water absorption and thermal conductivity of SW-AWBs were intensively studied. XRD, BET and SEM were combined to comprehensively investigate the microscopic mechanism. The experimental results indicate that as drying for 40 d and 140 d, the drying shrinkage of SW-AWBs with NaCl decreases by 69.5% and 14.4%, respectively. Conversely, NaNO3 and NaOH both increase the drying shrinkage, which is unfavourable to durability of SW-AWBs. In terms of frost resistance, NaCl significantly reduces the loss of mass and strength, because Cl- promotes the synthesis of Al-substituted tobermorite that refines the pore struc- ture of the system. The pore structure of SW-AWBs mixing with NaNO3 and NaOH are similar, mainly consisting of a single distribution of mesopores, therefore the water absorption is relatively large and frost resistance is poor. As for thermal conductivity, NaCl is more beneficial to the heat preservation of SW-AWBs relative to NaNO3 and NaOH. This paper provides a good reference to effectively reuse MSWI and further improve the durability of SW-AWBs prepared by MSWI and FA. (C) 2019 Elsevier Ltd. All rights reserved.