Foam concrete with untreated phosphogypsum and fly ash: strength and microstructure

Expanding the application scope of phosphogypsum (PG) is critically important for improving its utilization. In this study, a PG-based foam concrete was prepared using untreated PG, fly ash (FA), cement, and a foaming agent. The effects of foam content, FA content, water-to-binder (W/B) ratio, and PG content on the properties of PG–FA foam concrete were systematically investigated. Key performance parameters, including dry bulk density, water absorption, compressive strength, and frost resistance, were evaluated. Microstructural characteristics were examined using FTIR and SEM. The experimental results showed that the mixture containing 9% PG, 20% FA, and a W/B ratio of 0.35 exhibited optimal performance, achieving a compressive strength of 8.15 MPa and a dry bulk density of 860.06 kg/m³. An optimal amount of PG promotes ettringite formation through hydration reactions, thereby refining the pore structure and enhancing the mechanical properties of the foam concrete.