Research on Performance Optimization and Microstructure of Composite Cementitious Material System Incorporating Recycled Fine Powder

As a typical solid waste, recycled fine powder from waste concrete holds significant potential for enhanced resource utilization when used in the preparation of cementitious materials through multi-solid-waste synergistic composite activation. In this study, a recycled fine powder-based multi-component composite cementitious system was established by incorporating ground granulated blast furnace slag, calcium carbide residue, and phosphogypsum. The influence of each component on the mechanical properties and microstructure of the system was systematically investigated, followed by an interaction analysis using the response surface methodology. The results indicate that the alkalinity provided by calcium carbide residue forms the foundational guarantee for activating the system’s reactivity. The ettringite formed during the hydration of phosphogypsum effectively enhances the later-age strength and structural densification. Recycled fine powder can compensate for the strength development when the dosage of ground granulated blast furnace slag is reduced. The optimized composite system achieved a maximum 28-day compressive strength of 35.2 MPa, with optimal formulation ranges of Pc = 50–70%, Ps = 50–60%, and Pp = 8–12%. The synergistic effect between Pc and Ps is the dominant factor governing compressive strength, while the phosphogypsum dosage should be controlled within a suitable range through its interaction with Ps. This work provides a novel understanding of the synergistic activation mechanism among multiple solid wastes and offers a statistically optimized mix-design guideline for practical applications.