Development and performance evaluation of silty sand eco-concrete: alkalinity regulation and vegetation compatibility

Valorizing waste silty sand for ecological slope protection offers a sustainable waste management solution. This study developed a Silty Sand Eco-Concrete (SSEC) optimized via orthogonal experiments. The effects of key parameters, including silty sand ratio, water-to-binder ratio, and mineral admixtures, on mechanical strength, hydraulic permeability, and pore alkalinity were elucidated. Results indicated that the silty sand ratio dominated mechanical and hydraulic properties, while silica fume regulated pore pH via the pozzolanic effect. A strong porosity-permeability correlation was also established. To ensure vegetative compatibility, a synergistic “chemical-agronomic” strategy was implemented. Combining 0.2 mol/L FeSO 4 surface modification with 0.5% FeSO 4 substrate amendment maintained substrate pH < 7.5 for over 42 days. Post-vegetation assessment revealed that root-matrix interactions inevitably compromised mechanical integrity. Consequently, mixtures S-1 and S-2 were disqualified due to insufficient residual strength and porosity, respectively. The S-3 formulation (water-to-binder ratio 0.30, sand 5%, fly ash 10%, silica fume 7%) proved optimal, achieving a residual compressive strength of 9.2 MPa and maintaining the substrate pH < 7.5 for over 42 days, successfully balancing structural stability, hydraulic performance, and robust vegetation growth. These findings demonstrate the feasibility of upcycling waste silty sand into functional green infrastructure materials.