Study on Multi-Solid Waste Alkali-Activated Material Concrete via RSM

This study prepares solid-waste-based alkali-activated material (AAM) concrete using ground granulated blast furnace slag (GGBFS), fly ash (FA), steel slag (SS), and desulfurized gypsum (DG) as primary raw materials, with Na2SiO3 as the activator. Taking the GGBFS content (X1), Na2SiO3 content (X2), and water-to-binder ratio (X3) as independent variables and the 3-day, 7-day, and 28-day compressive strengths and slump as response values, it investigates the influence of each factor and their interactions, constructs a response surface prediction model, screens for the optimal mix proportion with comprehensive performance, and explores the microstructural characterization and strength formation mechanism of the AAM concrete via SEM and EDS. The results indicate the following: (1) compared with binary and ternary mixtures, the use of the quaternary solid waste mixture not only enhances strength and optimizes the microstructure but also increases the utilization rate of low-quality solid wastes; (2) the regression coefficients (R2) of the response surface models are all greater than 0.98, exhibiting good goodness of fit and rationality. Experimental validation confirms that each model shows excellent predictive capability; (3) AAM concrete exhibits comprehensively superior mechanical properties to ordinary cement, with leading early- and late-stage compressive strengths and splitting strengths, albeit with a slightly lower slump; (4) the performance synergy is prominent. Combined with microscopic analysis (highly polymerized C-S-H gels and a dense structure), the superiority of its macroscopic mechanical properties stems from the optimization of the microstructure, reflecting the intrinsic correlation of the “microscopic densification-macroscopic high strength.