Durability analysis of alkali-activated steel slag-GGBS-coal gangue composite mixtures

This study developed a low-carbon pavement base material utilizing steel slag, GGBS, and coal gangue activated by sodium silicate. The mixture proportions were optimized using the uniform design method, and the mechanical properties and durability were systematically evaluated. The results indicate that the system achieves optimal performance when the mass percentages of coal gangue, steel slag, GGBS, and sodium silicate are 52.6%, 36.8%, 6.3%, and 4.3%, respectively. Microscopic analysis (XRD, SEM, and FTIR) reveals that the alkali-activation process dissolves active components to generate substantial C-A-S-H gels and a dense three-dimensional network. Specifically, FTIR spectra confirm the depolymerization and subsequent reorganization of the aluminosilicate framework, providing the fundamental mechanism for the material's macroscopic performance. The optimal mixture achieved a 7-day unconfined compressive strength of 6.52 MPa, satisfying the requirements for high-grade highway bases. After five freeze-thaw cycles, the specimens maintained a strength retention rate exceeding 85% with a mass loss of less than 2%. Furthermore, due to sustained hydration, the strength increased by up to 37.5% after ten wet-dry cycles, demonstrating exceptional durability. This work provides a feasible and sustainable approach for the large-scale utilization of industrial solid wastes in green road engineering.