Strength characteristics and microscopic mechanism of polypropylene fiber and cement-stabilized dredged soil with foaming agent

This study explores the strength performance and microstructural evolution of dredged clay stabilized with cement, polypropylene (PP) fibers, and a protein-based foaming agent. Direct shear and unconfined compressive strength tests were conducted to evaluate the effects of PP fiber dosage (0–0.9%) and curing duration (3 h, 7 days, 28 days). Results indicate that fiber inclusion markedly improves both shear and compressive strengths, with optimal reinforcement observed at 0.6% fiber content. Increased curing time significantly enhanced strength, particularly during the first week, due to accelerated cement hydration. After 28 days of curing, the unconfined compressive strength rose from 950.4 kPa for the fiber-free sample to 1145.3 kPa at the optimal fiber content. However, excessive fiber addition led to agglomeration and weakened interfacial bonding. SEM observations revealed that cement hydration products formed a cohesive matrix by binding soil particles and filling pores, while PP fibers bridged microcracks and established a spatial load-transfer skeleton. This synergistic mechanism improved ductility and mitigated brittle failure. The protein-based foaming agent created a controlled porous structure that improves workability, supports hydration, and lowers material density. The integrated use of cement, proteinbased foaming agent, and PP fibers provides a balanced approach for strengthening and stabilizing dredged soils.