A novel struvite-modified planting concrete for sustainable slope protection and environmental restoration

Conventional dense concrete for slope protection enhances physical stability but impedes water-soil exchange and degrades ecological functions. Planting concrete offers a sustainable alternative, yet challenges remain in nutrient regulation and long-term plant support. Although nutrient-rich solid waste minerals hold great potential, their multifunctional roles in planting concrete have been rarely explored. Herein, a novel struvite-modified planting concrete (SPC) with balanced mechanical and vegetation performance was developed for sustainable slope protection and environmental restoration. Among the samples, SPC-6 exhibited optimal physical properties with a compressive strength of 13.1 MPa, splitting tensile strength of 2.1 MPa and porosity of 31.4 %, ensuring both structural strength and permeability (lowest coefficient: 4.5 mm/s). Struvite incorporation improved water absorption, alkalinity regulation and freeze-thaw resistance, with SPC-6 showing the lowest mass and strength loss after 50 cycles. Hydration heat and thermogravimetric analysis indicated enhanced hydration activity, with SPC-6 exhibiting the highest cumulative heat (97.3 J/g after 77 h) and the lowest residual mass (72.3 %). Correspondingly, SPC-6 was superior in vegetation performance with the highest recorded dry weight (0.087 g), protein content (5.3 mg/g), and chlorophyll content (2.3 mg/g), along with the highest 30-d nutrient accumulation (6.0 % total nitrogen and 9.4 mg/g total phosphorus) in the ryegrass plant. Nutrient leaching tests showed sustained N and P release, with SPC-6 reaching 22.2 mg NO₃^--N and 1.1 mg PO₄^3--P at 28 days, supporting improved plant growth. This study offers insights into multifunctional eco-concrete design, promoting physical stabilization and ecological restoration in environmental applications.