Combined Valorization of Engineering Waste Soil and Recycled Aggregates for Cement-Based Bricks: Freeze-Thaw Behavior, Multifactorial Optimization, and Quantitative Strength Modeling

This study addresses the freeze-thaw durability challenge of sustainable cement-based bricks in cold regions by investigating the compressive strength and mass loss behavior of recycled construction waste cement-based bricks (RCWCB) prepared by combining engineering waste soil (EWS) and recycled aggregates (RA). A four-factor, three-level orthogonal experimental design was conducted considering water-cement ratio, cement-EWS ratio, recycled fine aggregate-EWS ratio, and compound admixture-to-total raw materials ratio. A total of 180 specimens were tested after 0, 15, 30, and 45 freeze-thaw cycles to characterize the degradation process. The results show that cement-EWS ratio (primary) and compound admixture dosage (secondary) are the dominant factors affecting freeze-thaw resistance: increasing these two parameters reduced the 45-cycle strength loss by up to 25% and mass loss by 0.73%. Through regression modeling and response surface analysis, a model-predicted durability-optimized mix proportion was obtained: water-cement ratio of 0.6, cement-EWS ratio of 0.35, recycled fine aggregate-EWS ratio of 0.4, and compound admixture dosage of 10%. Under this optimum, the 28-day compressive strength reached 16.5 MPa, and the strength loss rate after 45 freeze-thaw cycles was only 12.4%. Furthermore, a unified nonlinear prediction model integrating mix parameters and freeze-thaw cycle times was established, with predicted-to-measured ratios ranging from 0.98 to 1.02. This study verifies the technical feasibility of synergistic valorization of EWS and RA for frost-resistant bricks, and provides a quantitative design tool for durability-oriented mixture optimization and strength prediction of sustainable masonry materials in cold regions.