Impact of using recycled plastic particles as a partial replacement of aggregates on the mechanical performance of the eco-friendly concrete

The current work contributes to the protection of natural raw resources and reduces environmental effects by recycling plastic in sustainable construction techniques. By investigating the exact transition point from a strength reducer to a functional benefit of plastic waste in the production of lightweight concrete, using coarse aggregates versus fine aggregates separately under the same curing conditions. Recycled polyethene (PE) waste, produced through thermomechanical extrusion and pelletizing, was used as a partial replacement of coarse and fine aggregates at 2.5%, 7.5% and 15% by weight. Seven concrete mixes of M25 were cast and tested for compressive strength, splitting tensile strength, and absorption rate after 7 and 28 days of curing. Findings indicated that the highest workability was achieved by replacing 15% of plastic particles with coarse aggregate (about 135 mm), while 2.5% PW had the lowest workability (about 45 mm) by replacing fine aggregate. While the highest compressive strength was obtained with a 2.5% replacement of fine aggregate, reaching about 26.22 MPa. In contrast, it decreased more severely when reaching 15% by about 21.11 MPa, compared to replacing coarse aggregates with plastic particles by about 22.44 MPa. Furthermore, substituting sand with recycled plastic particles at 2.5% replacement level resulted in the best splitting tensile strength of 1.69 MPa. It is noted that substituting coarse aggregates reduced the density more than fine aggregates, with the peak reduction rate being 3.66% for cube specimens after replacing 15% of coarse aggregates at 28 days, making it the most efficient replacement for producing lightweight concrete. All replacement levels of sand increase absorption rates by 10.4% over coarse aggregate. Therefore, these results are highly transferable to field conditions for non-structural applications such as pedestrian pathways and paving blocks, provided that workability is optimized.