Sustainable conversion of low-grade industrial solid wastes into low-density foamed concrete via synergistic activation and cascade utilization

In the global effort to reduce pollution and carbon emissions, the valorization of low-grade solid waste and the decarbonization of construction materials remain significant challenges. This study proposed a sustainable conversion pathway from low-grade solid waste→composite cementitious materials (CCMs)→high-performance foamed concrete (FC) through synergistic activation and cascading utilization. The findings indicated that the hydration processes of solid waste-based iron-rich calcium sulfoaluminate (IR-CSA) clinker, phosphogypsum (PG), and low-reactivity slag exhibited notable synergistic effects and asynchronous characteristics. The hydration of clinker and excess PG mainly occurred in the early stages, while slag was slowly activated under low alkalinity and persulfate conditions, continuously forming C-(A)-S-H gel and new AFt in the later stages. Slag substitution enhanced the long-term performance stability of CCM while causing changes in porosity, hydration phase proportions, and microstructural morphology. CCM containing only 15% clinker achieved a 180-day compressive strength of 74.3 MPa. During FC preparation, the setting characteristics of the composite pastes effectively accommodated the expansion behavior induced by H₂O₂ foaming. All FC samples exhibited a specific compressive strength exceeding 4.77 N m/kg, with the lowest thermal conductivity recorded at 0.136 W/m·K. The sustainability assessment demonstrated that FC was safe and environmentally friendly. Furthermore, the life-cycle carbon footprint per unit of specific strength for FC was reduced by 15.41%–61.29% compared to autoclaved aerated concrete. These results highlight the potential of this technology in advancing sustainable construction practices and promoting the valorization of industrial waste.