Waste-Plastic Strips for Reinforcing Pavement Subgrade Soil: Mechanisms, Performance, Sustainability and Research Needs

Abstract

Randomly distributed strips cut from post-consumer plastic offer a potential method to improve weak pavement subgrades while creating an engineered reuse route for difficult-to-recycle films, pouches, and bottles. This review critically synthesizes the mechanisms, material variables, laboratory performance, pavement implications, and environmental safeguards associated with strip-reinforced soil. The evidence shows that improvement arises from interface friction, edge bearing, pull-out resistance, tensile bridging, lateral confinement, and crack interception. These mechanisms are not activated uniformly; their contribution depends on polymer stiffness and surface condition, strip length, width, thickness and aspect ratio, dosage by dry soil mass, soil gradation and plasticity, moisture state, compaction energy, and mixing quality. Across published studies, moderate plastic contents commonly increase California bearing ratio (CBR), unconfined compressive strength, shear strength, stiffness, and post-peak ductility. However, the response is usually non-monotonic because excessive strip content displaces mineral particles, lowers dry density, encourages folding and clustering, and creates locally weak or poorly compacted zones. In the benchmark dataset examined in this review, cleaned low-density polyethene strips measuring 5 mm × 30 mm (aspect ratio 6) at 3% of dry soil mass produced the best common laboratory condition for three soils. Soaked CBR increased from 4.25%, 5.82% and 3.40% to 8.46%, 12.74% and 6.28%, respectively, while maximum dry density remained largely retained. Nevertheless, this optimum is material- and process-specific and should not be generalized without replicate statistics and complete geometry–dosage matrices. A practical design framework is therefore proposed that treats strength, compactability, constructability, durability, and environmental containment as simultaneous acceptance criteria. Before routine field adoption, the technology requires repeated-load and rutting tests, wet–dry and temperature cycling, abrasion and leaching assessment, microplastic-release controls, quality-controlled mixing procedures, and monitored trial pavement sections.