Performance Control and Synergistic Modification Mechanism of Phosphogypsum-Based Cementitious Materials

This paper focuses on the resource utilization of phosphogypsum, a major industrial by-product from phosphate fertilizer production, in highway engineering materials, exploring its performance optimization and collaborative modification mechanisms. Phosphogypsum, primarily composed of CaSO4·2H2O, faces challenges such as acidity (pH ≈ 3.56), poor water resistance, and strength limitations, which hinder its engineering application. This study investigates pretreatment methods (e.g., lime neutralization, physical grinding) and the synergistic effects of additives like metakaolin, steel slag, slag powder, and stone powder. The results show that adjusting phosphogypsum’s pH to 10 via lime neutralization significantly improves its mechanical properties, with its 28-day compressive strength increasing by 21%. The optimal dosage of cement as an alkaline activator is 4%, while steel slag performs best at 10%. Metakaolin (11% dosage) enhances the 28-day strength of 30% phosphogypsum-containing systems by 89–114% through pozzolanic reactions, forming a high-strength aluminosilicate network, enabling the preparation of C35 concrete with a 28-day strength of 44.5 MPa. Additionally, stone powder exhibits the most effective strength improvement, with the 56-day strength increasing by 12.5 MPa compared with the reference group. Economically, utilizing 30% phosphogypsum and 11% metakaolin reduces C35 concrete costs by 15–20%. This research provides theoretical and technical support for the large-scale application of phosphogypsum in highway engineering, addressing environmental and economic challenges.