Study on the crushing properties of channel dredged sludge for rapid drying and reclamation utilization

To ensure the efficient operation of navigable waterways and protect water resources, numerous river dredging and regulation projects are carried out annually in China. These projects generate large quantities of dredged sludge, characterized by high water content, low strength, and high compressibility. Traditional natural air-drying methods for this sludge require extensive land areas and are highly susceptible to unpredictable weather conditions. Consequently, rapid drying and soil improvement are essential for its subsequent resource utilization. Furthermore, the subsequent crushing process is critical; neglecting it not only increases labor and time costs and raises the risk of machinery damage, but also severely compromises the final construction quality. Thus, there is an urgent need to quantitatively evaluate the impact of rapid drying and improvement processes on the mechanical crushing performance of the sludge. Addressing this gap, and considering the specific strength range and plastic state characteristics of solidified sludge, this study proposes a novel testing apparatus and a quantitative evaluation method based on the impact crushing tests. Currently, there are no standardized testing protocols or dedicated devices available for evaluating the crushing performance of dried and improved dredged sludge. Drawing on agricultural soil crushing studies and standard specimen dimensions from geotechnical direct shear tests, a specialized testing apparatus was developed. Based on the definition of soil aggregates, a critical size limit of 10 mm was adopted to represent a stable clod structure; particles smaller than this threshold were considered to meet the crushing criterion. This setup enabled the accurate determination of the sludge's surface binding energy before and after treatment. Using the self-developed device alongside a conventional direct shear apparatus, the effects of initial water content, drying material types (Ordinary Portland Cement, sulphoaluminate cement, lime, fly ash, and S95 slag powder), and their dosages on the macroscopic cohesion and microscopic surface binding energy of the improved sludge were systematically examined. The results indicate that: (1) regardless of the addition of drying materials, the internal cohesion of the sludge consistently increases as water content decreases; (2) Ordinary Portland Cement and sulphoaluminate cement significantly increase the maximum achievable cohesion; (3) lime and fly ash have a limited effect on cohesion; and (4) when the S95 slag powder dosage exceeds 10%, cohesion decreases slightly before stabilizing. Furthermore, as cohesion increases and water content decreases, the variation in minimum surface binding energy generally corresponds to the optimal water content for practical soil drying and crushing operations. Compared with traditional cohesion indices, surface binding energy serves as a more effective parameter for quantitatively evaluating the crushing difficulty of treated soil. The minimum surface binding energy notably increases with higher dosages of Ordinary Portland Cement and sulphoaluminate cement. Conversely, for lime, fly ash, and S95 slag powder, this minimum value decreases as the dosage increases. Specifically, when the lime dosage exceeds 30%, the minimum surface binding energy of the soil mass can be drastically reduced to 200 J/m². This study provides a feasible and scientifically grounded approach for the quantitative evaluation of the drying and crushing performance of dredged sludge, facilitating its large-scale sustainable resource utilization.