Reconciling strength and alkalinity in cast-in-place ecological concrete via spray-induced phosphate mineralization

ABSTRACT Conventional ecological concrete (EC) struggles to balance mechanical strength with low alkalinity for plant growth. This study proposes a spray-mediated phosphate mineralization strategy using diammonium hydrogen phosphate (DAP) and dipotassium hydrogen phosphate (DPP) to induce in-situ calcium phosphate precipitation in cast-in-place EC. The treatment effectively reduced pore alkalinity and maintained excellent pH stability, with long-term fluctuations below 0.3 units. Phosphate-induced mineralization refined the pore structure and enhanced compressive strength while preserving ecological functionality. A gradient mineralization pattern was observed, with greater hydroxyapatite coverage and phosphorus enrichment near the treated surface. Under the optimal condition, specimens achieved a 17.1% pH reduction to 8.7, a 13.7% increase in compressive strength, and only a 1.1% decrease in continuous porosity. Vegetation compatibility improved markedly, with 45% higher seed germination and 48.5% greater shoot elongation. These results demonstrate the field applicability of spray-induced phosphate mineralization for cast-in-place EC.