The influences of MSWI fly ash washing and blast furnace slag/bottom ash ratio on low-carbon cementitious materials

The heavy metal and soluble salt content in municipal solid waste incineration fly ash (MSWI FA) negatively affects the leaching safety of cementitious material, thereby impacting their corrosion resistance and durability. In this study, an MSWI FA washing pretreatment was conducted to obtain WFA1, and a low-carbon, low-cost cementitious material (FBM) was prepared in combination with bottom ash (BA). The optimal ratio parameters determined through orthogonal experiments were a mass ratio of 51% blast furnace slag (BFS), 17% BA, 20% WFA1, and 12% flue gas desulfurized gypsum (FGDG). The FBM containing WFA1 exhibited strong macroscopic performance, with a compressive strength of 37.42 MPa for FB2 at 28 days. The leaching concentrations of Pb, Zn, As, and Cd met the standards for underground Class II water quality. The leaching concentrations of Cl- and SO42- were in the ranges of 90-200 mg/L and 20-100 mg/L, respectively. The reduction in the BFS/BA ratio led to decreased polymerization degree (RBO = 0.310) and chain length (MCL = 2.627) of C-(A)-S-H gel, along with a decrease in Al [VI] content in ettringite (22.63%). Furthermore, Cl- played a stronger role than SO42- in the generation of Friedel's salt. The economic benefit of producing one ton of FB2 was calculated to be 38.60 USD, with CO2 emission of only 10.97 kg. The ultimate aim of this study was for waste-generating enterprises to achieve internal synergy in the disposal of solid and hazardous waste, thereby creating a "zero-waste company and group."