Watermelon vine as dual-functional additive in ecological porous concrete

Abstract

Ecological porous concrete (EPC) is constrained by a persistent trade-off: the dense cementitious matrix required for strength reduces porosity and generates a highly alkaline pore environment (pH > 11) inimical to plant growth. To address this, the present study investigates watermelon vine (WV), an abundant agricultural waste, as a dual-functional additive that simultaneously provides physical reinforcement and chemical alkalinity regulation. An integrated orthogonal array–response surface methodology–entropy-weighted TOPSIS framework was established for multi-objective mix optimisation. WV content was identified as the dominant factor governing pore pH, reducing it to 7.6 at an optimal dosage of 3 wt% within 14 days. The optimised mix—comprising 16–20 mm coarse aggregate, 20 wt% fly ash, a water-to-binder ratio of 0.26, and 3 wt% WV—achieved a compressive strength of 10.4 MPa and an effective porosity of 27.7%, with compressive strength remaining stable at 60 d. Scanning electron microscopy revealed a dense interfacial transition zone containing crystalline products morphologically consistent with calcium oxalate, and plant germination tests confirmed vegetation establishment exceeding 80% coverage within 60 days. These converging lines of evidence support an in-situ acid–base neutralisation mechanism, positioning WV as a viable, low-cost functional resource for sustainable construction.