Sustainable utilization of waste carbon black for self-sensing cement-soil composites in silty soil ground improvement

To achieve industrial waste utilization and address the challenges of silty soil ground improvement and monitoring, this study investigates the effects of carbon black (CB) from petrochemical waste on the mechanical, electrical, and self-sensing properties of cement-soil (CS). Using polyethylene oxide (PEO) as a dispersant in combination with physical techniques for dispersing CB, a comprehensive evaluation was conducted to quantify the impacts of CB properties, dosage, and curing period on key properties of cement-soil, including fluidity, density, unconfined compressive strength (UCS), and electrical resistivity (ER), self-sensing. Microscopic analysis techniques and mechanistic modeling were used to reveal the improvement and self-sensing mechanisms of 254CB (specific surface area (SSA) of 254 m 2 /g)-reinforced cement-soil. The results show the selection of reasonable CB types can significantly improve cement-soil properties: 0.62CB enhanced UCS, while 254CB reduced ER. The incorporation of 0.62CB (SSA of 0.62 m 2 /g) improved the fluidity, density and UCS of CS, and the addition of 5.0 wt% 0.62CB exhibited UCS values of 2.1, 3.1, and 3.8 MPa at 7, 28, and 90 days, corresponding to increases of 31.3%, 29.2%, and 22.6%, respectively, compared to CS. The pretreated 254CB-reinforced CS (7.0 wt%) achieved an ultralow ER of 195 Ω·cm at 14-day, a two-orders reduction than CS. The 254CB-reinforced CS composite demonstrated significantly improved stress sensitivity (up to 41.3), enabling real-time monitoring. Microstructural refinement via pretreated 254CB suppressed agglomeration and enhanced percolation networks, directly correlating with mechanical, electrical, and self-sensing enhancements. These findings indicate that the pretreated waste CB-reinforced cement-soil holds significant potential as a conductive material for real-time monitoring of the construction quality of soft ground improvement.