Effects of curing methods on microstructure, mechanical properties, and heavy metal immobilization in non-sintered MSWIFA-based lightweight aggregates

Abstract

With the rapid economic growth and accelerated urbanization, solid waste recycling has become a critical priority for eco-friendly urban development. Although some studies have investigated cold-bonded aggregates using MSWIFA, the effect of curing environments on heavy metal immobilization and mechanical behavior remains poorly understood. This study utilizes solid wastes such as municipal solid waste incineration fly ash (MSWIFA) and carbide slag to produce environmentally friendly non-sintered lightweight aggregates, and the effect of curing temperature and solution on the properties, reaction products as well as heavy metal leaching was investigated. The results show that under steam curing at 60 °C for 12 h, using calcium carbide slag supernatant as the granulation solution, the mechanical strength of the aggregates reached more than 7.02 MPa, meeting the Chinese standards for lightweight aggregates. Steam curing promotes the formation of hydrocalumite minerals, but the peak gradually weakens when the curing temperature reaches 75 °C. Microstructural analysis through XRD, FTIR, SEM, and XPS revealed that high temperatures activated the latent reactivity of slag, accelerating the reactions and promoting the generation of more C-S-H gel and hydrated calcium aluminates. This study proposes an innovative use of MSWIFA and carbide slag to produce non-sintered aggregates and systematically evaluates their performance under various curing conditions. The results are validated by detailed characterization, confirming both the originality and reliability of the work. In conclusion, the non-sintered lightweight aggregates prepared from MSWIFA demonstrate good mechanical performance and environmental adaptability, providing a sustainable alternative to natural aggregates and a useful reference for eco-friendly construction materials.