Biochar-based stabilised dredged sediment substrates: strength and vegetation performance

Dredged sediments present significant disposal challenges due to poor mechanical properties, high salinity, and limited nutrient availability, restricting their reuse in ecological restoration. This study evaluates the synergistic effects of biochar, ground-granulated blast furnace slag (GGBFS), and gypsum on the geotechnical, biochemical, and ecological performance of dredged sediment substrates. Four treatments were investigated: CK (100% dredged sediment), T1 (15% biochar, 10% GGBFS, 15% gypsum), T2 (10% biochar, 20% GGBFS, 10% gypsum), and T3 (7.5% biochar, 25% GGBFS, 7.5% gypsum), all with 60% sediment. Performance was assessed using unconfined compressive strength (UCS), X-ray diffraction (XRD), scanning electron microscopy (SEM), plant growth trials using Lolium perenne (ryegrass), and biochemical analyses. UCS increased markedly from 40.2 kPa (CK) to 3057.2 kPa (T3) at 60 days, with XRD and SEM indicating enhanced cementitious bonding. Durability was evaluated using controlled dry–wet cycling, with T3 showing the lowest strength loss (10.6%) and T2 showing moderate loss (20%), indicating improved resistance to cyclic environmental conditions. However, plant trials revealed stress and necrosis under T2 and T3, whereas T1 supported healthy growth, improved chlorophyll content, reduced electrical conductivity, enhanced nutrient availability, and increased microbial enzyme activity. Overall, T1 represents a balanced and promising option under laboratory conditions, although further validation under field conditions is required for practical application.