High-porosity vegetated concrete with dredged silt for sustainable slope protection: mechanical properties and anti-scouring performance evaluation

To address the challenge of achieving a balance among mechanical strength, vegetation performance, and anti-scouring capacity in traditional eco-revetment engineering, this study introduces a novel high-porosity vegetated concrete that incorporates dredged silt for effective resource management. For the first time, dredged silt has been employed as an alkali-reducing substrate within the mix design, which was developed by optimizing the gradation of coarse aggregates to mitigate soil erosion and ecological degradation along riverbanks. Extensive investigations were conducted to evaluate the effects of coarse aggregate size, water-to-cement ratio, and mineral admixtures on porosity, compressive strength, and permeability. In addition, comparative alkali-reduction experiments, combined with XRD, XRF, and SEM analyses, were conducted to clarify the respective roles of dredged silt and FeSO₄ and to further reveal the microstructural mechanisms of the substrate–concrete system. Furthermore, the alkaline environment was regulated using the optimally proportioned dredged silt mix to perform planting experiments, and its anti-scouring performance was subsequently assessed. The results indicated that under optimal conditions with a coarse aggregate size between 25 and 30 mm, the 28-day compressive strength reached 6.23 MPa, with a porosity of 33% and a permeability coefficient of 3.3 mm/s. When compared to conventional mixtures, the proposed mix exhibited an increase in compressive strength by approximately 40% to 60% at similar porosity levels, along with a 30% increase in porosity at equivalent strength levels. The incorporation of dredged silt effectively reduced alkalinity, lowering the pore environment pH from 8.7 to 7.3, which significantly enhanced the ecological environment and promoted vigorous vegetation growth. The comparative pH test showed that FeSO₄ mainly contributed to the reduction in pH at the early stage, whereas dredged silt provided a sustained buffering effect during the later curing period; the combined treatment exhibited the best long-term performance. XRD and XRF results indicated that the principal mineral framework of the dredged silt remained generally stable after vegetation growth. SEM observations further revealed that typical hydration products, such as AFt and C–S–H gel, were present in the original concrete, whereas the amount of AFt decreased after vegetation growth, suggesting continued microstructural evolution of the cementitious matrix. Anti-scouring tests revealed that the soil-covered planted concrete group experienced the least erosion, with a reduction of 32.6% compared to the soil-covered unplanted concrete group and a 78.1% reduction compared to the virgin soil group at a flow velocity of 1.0 m/s. The developed material exhibited synergistic protection among soil, concrete, and vegetation, demonstrating excellent soil and water conservation as well as effective ecological slope protection performance. This article introduces a reliable and sustainable material for riverbank protection and offers a new pathway for the high-value utilization of dredged silt resources.