Pore structure control of self-foamed geopolymers incorporating municipal solid waste incineration fly ash via metal stearates

Pore structure control is a key factor governing the mechanical and thermal performance of self-foamed geopolymers. In this study, calcium stearate (CS), sodium stearate (SS), and zinc stearate (ZS) were incorporated into MSWIFA-based self-foamed geopolymers to improve the foam stability, and the effects on the engineering properties were investigated. The stearates increased the viscosity through hydrophobic particle agglomeration and formed stabilizing hydrophobic films around the bubbles, which reduced bubble coalescence and escape. With 0.5 wt% ZS, the expansion ratio and porosity increased by 5.5 and 6.9 pp, respectively, compared with those of the control, whereas the thermal conductivity decreased by approximately 29%. Although higher porosity generally reduced compressive strength, CS and SS supplied additional ions that increased geopolymerization and compressive strength as the dosage increased. In contrast, ZS supplied zinc ions that inhibited alkaline activation, thereby reducing compressive strength. All the mixtures satisfied the heavy metal leaching limits defined by the United States Environmental Protection Agency (USEPA), even with 10 wt% MSWIFA.