Recycling of waste glass in lightweight geopolymer using incineration bottom ash as a foaming agent: Towards energy conservation

A large amount of waste glass and municipal solid waste incineration bottom ash (IBA) generated in municipalities is a serious environmental issue. For energy conservation purpose, this study aimed to develop a novel thermal insulating lightweight self-foaming geopolymer (SFG) material using waste glass as the main precursor and IBA as a foaming agent. The microstructure was investigated by XRD, FTIR, NMR, MIP and SEM-BSE techniques to reveal the mechanisms of the foaming process and geopolymerization reaction. The results showed that the use of 100% waste glass powder (WGP) as the precursor led to a connecting-cracked matrix due to silica gel shrinkage. However, the cracking was significantly alleviated when 50% IBA was incorporated as IBA contributed to more stable C-(N)-A-S-H (calcium silicate hydrate substituted with Al and Na) production as well as spherical pores formation to mitigate crack propagation. The SFG prepared with 50% IBA exhibited a geopolymer matrix with more regular and independent pores than that prepared with 100% IBA. This was because the high metallic Al content in IBA generated an excessive amount of hydrogen gas, resulting in the development of irregular and interconnected pores. Given the stability of the reaction products with fewer cracks and a uniform pore structure, the SFG prepared with 50% IBA and 50% WGP exhibited satisfactory functional properties (low density and thermal conductivity as well as desirable compressive strength), indicating a great potential for energy saving and environmental protection.