Unraveling pH evolution driven by multi-component synergy and plant feedback in cement-based vegetation substrate

Cement-based vegetation substrate (CBVS) provides dual benefits for ecological restoration and slope engineering stabilization, yet its alkaline environment poses a major challenge to plant survival. This study investigates the evolution of pH in a vegetation-compatible cementitious system incorporating silica fume and a composite ecological regulator (CER). Through SEM and vegetation experiments, we reveal multi-component alkaline-regulation mechanisms and demonstrate bidirectional feedback between plant growth and substrate pH. Cement content was identified as the primary factor controlling initial alkalinity. The CER effectively reduced alkalinity via acidic ion neutralization, humate complexation, and microbially induced precipitation, achieving a maximum pH reduction of 11.2% at a 0.3% dosage. Concurrently, a 2% silica fume content consumed portlandite to form low-alkalinity C-S-H gels, decreasing pH by 5.2% while improving matrix strength. Notably, Tall fescue exhibited the strongest adaptability and further reduced the system pH by 15.7% after 100 days, confirming a significant plant-material feedback loop.