Experimental investigation on thermal and mechanical performance of alkali-activated coal gangue foam materials doped with phosphogypsum

Using low-grade solid wastes to prepare building foam insulation materials can effectively reduce environmental pollution and building energy consumption. However, their poor gelling activity results in poor mechanical and thermal insulation properties. In this study, alkali activated foam material was successfully prepared using coal gangue (CG) as the main component, with phosphogypsum (PG) added to improve activation and pore quality. An orthogonal experiment with six factors and five levels was designed to comprehensively explore the influence mechanism and optimal dosage of polypropylene fibers (PPF), expandable polystyrene (EPS) particles, and alkali activators. The results show that: (I) An appropriate amount of PG can effectively promote the reaction and assist in the formation of pores in the foam, which is attributed to the fact that PG can preferentially and rapidly dissolve and participate in the reaction to generate ettringite under strong alkaline environment. (II) An alkali activator with a modulus of 1.1 and a Na₂O content ranging from 10 to 12% optimizes both the mechanical and thermal insulation properties. It enables foam materials with a density of 536 kg/m³ to achieve a compressive strength of 3.68 MPa while maintaining a thermal conductivity of 0.1033 W/(m·K). (III) EPS particles and PPF further enhance compressive strength and thermal insulation by stabilizing the foam and maximizing PPF tensile properties utilization. These results indicate that the combination of EPS particles with PPF and PG can effectively improve the performance of alkali-activated solid waste foam materials.