Preliminary study on recycled plastic in shotcrete: mechanical properties and engineering application

This study examines the performance of shotcrete incorporating recycled plastic aggregate and polyacrylamide (PAM) for the Fenghuangshan Tunnel Project, via laboratory tests and field validations on slump, compressive strength, rebound rate and microstructures. Plastic aggregate reduces slump, yet optimal PAM dosage enhances cement paste cohesion and uniform plastic particle distribution. While higher plastic content lowers compressive strength, PAM mitigates this by densifying the interfacial transition zone, yielding a 15% rise in 28-day strength for mixtures with 10% plastic aggregate. Microstructural analyses show PAM promotes homogeneous hydration product formation on plastic surfaces and reduces pores and microcracks. Field trials of the optimised mix (10% plastic aggregate + 0.03 kg/m³ PAM) cut rebound rate by 1.04% and achieved a 28-day compressive strength of 32.7 MPa (8.6% higher than conventional mixtures). These findings confirm the engineering feasibility of this approach and the sustainable application of recycled plastics in shotcrete while meeting required construction performance.