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Synergistic impact of recycled PET microparticles on the mechanical performance of high-strength and conventional concretes
Summary
This paper isn't about human health directly—it's about turning recycled plastic bottles (PET) into an ingredient for concrete instead of sending them to landfills. Researchers found that replacing more than 5% of the sand in concrete with crushed plastic makes the concrete noticeably weaker, so they recommend keeping plastic content low and reserving this approach for non-load-bearing uses like sidewalks or decorative structures rather than buildings or bridges.
The global plastic waste crisis demands innovative recycling, such as using recycled polyethylene terephthalate (PET) microparticles as a replacement for natural fine aggregate in concrete. In this study, the volumetric substitution of PET particles (0%, 5%, 10% and 15% by sand weight) on the mechanical properties of conventional concrete (CC) (target compressive strength fc′ = 33 MPa) and high-strength concrete (HSC with 5% microsilica gel + 1% superplasticiser (target fc′ = 45 MPa) was examined, using 144 specimens tested at 7 and 28 days. PET incorporation consistently reduced the compressive strength, splitting tensile strength and modulus of elasticity (MoE). At 10% substitution, fc′ decreased by 24% in CC (from 33 MPa to 25 MPa) and by 22% in HSC (from 45 MPa to 35 MPa). At 15% PET, the reductions were 45% and 31%, respectively. The HSC showed better compressive strength retention but a greater loss in MoE (up to 34% at 15% PET). Unlike studies on PET fibres or macro-recycled aggregates, this work provides the first simultaneous multi-property quantification (here termed ‘synergistic’) of PET microparticle effects across both CC and admixture-optimised HSC, revealing matrix-dependent divergent degradation patterns through volumetric substitution. A practical 5% upper limit is recommended for non- and semi-structural applications, balancing waste utilisation with performance.