Experimental study on the physical-mechanical properties and vegetation performance of ecological concrete made with volcanic rock aggregates

Ecological concrete is a sustainable material that supports vegetation growth and promotes ecosystem restoration. However, its development is constrained by material limitations and insufficient understanding of vegetation-concrete interactions. Although the preparation process and water purification performance of ecological concrete made with volcanic rock aggregate have been preliminarily reported, key properties such as microstructure, porosity, pH, and long-term vegetation adaptability remain insufficiently investigated. In this study, ecological concrete using volcanic rock aggregate was prepared. The mix design and preparation process were optimized, and compressive strength, porosity, pH, microstructure, alkalinity reduction, and vegetation performance were systematically evaluated. The results showed that ecological concrete made with volcanic rock aggregate exhibited favorable physical-mechanical properties, with a 28-day compressive strength of 5.5–9.1 MPa, an effective porosity of 23.0–27.4%, and a reducible pH of 8.3. Optimal performance (24.4% porosity and 9.1 MPa strength) was achieved at an aggregate-to-cement ratio of 3.5. The compressive strength and porosity were jointly affected by the mix proportion, preparation method, and internal pore structure of the volcanic rock aggregate. The combination of low-alkalinity sulfoaluminate cement and a 2% oxalic acid solution effectively reduced alkalinity; however, the oxalic acid concentration, spraying volume, and treatment frequency must be carefully controlled to minimize adverse effects on microscopic morphology. In addition, the concrete demonstrated satisfactory vegetation performance. After nine months, the average grass height reached 52.0 cm. Roots extensively penetrated specimens with thicknesses of 6 cm, 8 cm, and 10 cm, with penetration resistance gradually increasing; penetration was markedly inhibited in 15 cm thick specimens. Therefore, a concrete thickness of 6–10 cm is recommended.