Synergistic effects on the geomechanical properties and microstructural mechanisms of nano-CaCO3 stabilized clay reinforced with recycled polypropylene fibers

This study examines the influence of nano-CaCO3 powder as a stabilizing additive and recycled polypropylene (PP) fibers as a reinforcing agent on the undrained shear strength of clay. A series of laboratory experiments were conducted on clayey soil samples both with and without these additives. The fiber content varied between 0.2% and 1% of the soil’s dry weight, while the nano-CaCO3 content ranged from 0.2% to 1.2%. Unconfined compressive strength (UCS) tests were performed under controlled conditions. The findings demonstrate that nano-CaCO3 significantly enhances clay stiffness and increases undrained cohesion through ion exchange, pozzolanic reactions, and the formation of calcium silicates and aluminates. The highest strength improvement in non-reinforced samples was observed at a nano-CaCO3 content of 0.8%, resulting in a 28% increase in undrained cohesion. However, further increases in nanomaterial content led to a diminishing rate of strength enhancement. Additionally, incorporating recycled PP fibers improved soil stiffness, enhanced ductility, and increased the strain at failure. The combined application of nano-CaCO3 and recycled PP fibers yielded a substantial improvement, leading to an 85% increase in undrained cohesion compared to untreated clay. These results highlight the synergistic effects of chemical stabilization and fiber reinforcement in enhancing the mechanical properties of clayey soils.