Effect of root growth on the key properties of recycled vegetated concrete

In recent years, vegetated concrete has been widely applied in the ecological restoration and landscape construction of river and lake embankments. To investigate the influence of plant root growth on the key properties of recycled vegetated concrete (RVC), this study systematically analyzed the evolution of the physical and mechanical properties of RVC before and after the growth of ryegrass roots. Sixteen groups of RVC test blocks with different mix proportions were prepared. After reducing the pH of the test blocks to 8.4 using ferrous sulfate solution, an 80-day ryegrass planting experiment was conducted to comprehensively evaluate plant growth performance. The effects of root growth on the continuous porosity, permeability coefficient, compressive strength, and pH of RVC were measured, and the microscopic mechanisms were revealed using XRD and SEM. The results showed that natural aggregate concrete was most conducive to ryegrass growth, but test blocks incorporating 10% recycled aggregate and 15% fly ash achieved similar ecological benefits, demonstrating potential as a substitute. Root growth reduced RVC continuous porosity by 2.95%–6.94% and permeability coefficient by 0.84%–4.88%; compressive strength varied from −2.07% to 2.93%, while pH increased by 5.92%–12.58%. Microscopic analysis revealed that the humid root environment promoted continued hydration of unreacted materials, consuming Ca(OH)₂ to form CaCO₃ and C-S-H gel, which repaired microcracks. This primarily explains the strength increase in some blocks and the porosity and permeability reduction. Meanwhile, CO₃²⁻ hydrolysis from CaCO₃ dissolution caused weak alkalinity, leading to pH rebound. This study elucidates root growth's bidirectional regulation on RVC performance and clarifies the synergistic effects of recycled aggregates and admixtures, providing a theoretical basis for RVC application in ecological slope protection.