Optimization formulation of low carbon MSWIFA cement-based composites modified by nano SiO2

The cementitious technique shows great potential as a solidification/stabilization treatment in the disposal of municipal solid waste incineration fly ash (MSWIFA). The utilization of MSWIFA as a supplementary cementitious material (SCM) offers the potential to substitute cement, thereby mitigating greenhouse gas emissions associated with conventional cement production. However, the lower active silicon content in MSWIFA diminishes its pozzolanic properties as an SCM. This paper explores a green and efficient pre-treatment approach for raw MSWIFA, and the treated MSWIFA was utilized as a SCM. The nano SiO2-modified MSWIFA cement-based composite (NMCC) was prepared by incorporating silicon-rich nano SiO2 (NS) to enhance the properties of the cementitious composite containing MSWIFA. The effects of MSWIFA content, water-to-binder ratio, and NS content on the NMCC were investigated in regards to its mechanical properties (compressive and flexural strength), fresh properties (fluidity and dynamic yield stress), and greenhouse gas emission (embodied carbon). The proportion and performance of NMCC were optimized by orthogonal experimental design. Range and variance analysis were applied to obtain the optimal formulation of NMCC. The findings suggest that NS can serve as an additional source of silicon to insufficient strength of cement-MSWIFA composites, which is attributed to the inadequate presence of silicon elements in MSWIFA. The comprehensive index analysis identified the NMCC with 15 wt% MSWIFA, 0.45 water-to-binder ratio, and 1.0 wt% NS as the optimal proportion. The optimal NMCC reduces embodied carbon by 38.91 kg CO2e/m3 compared to the cement control group, and can be effectively utilized in low-carbon buildings and engineering applications.