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Mechanical, Thermal, and Non-Destructive Evaluation of Concrete Incorporating Recycled PET Bottle Aggregates
Summary
Researchers incorporated recycled PET bottle aggregates into concrete at up to 30% replacement of natural aggregate, finding that 10% fine PET slightly improves compressive strength while higher substitutions reduce strength by up to 31%, though thermal conductivity drops by up to 42%, making PET-based concrete promising for lightweight insulating applications.
Abstract The valorization of post-consumer polyethylene terephthalate (PET) bottle waste in concrete represents a promising approach toward more sustainable construction materials. This study investigates the influence of recycled PET aggregates, used as partial volumetric replacements for natural sand and gravel, on the fresh, physical, mechanical, thermal, ultrasonic pulse velocity (UPV), and microstructural properties of concrete. Recycled PET bottles were processed into fine (FPET) and coarse (CPET) aggregates and incorporated at replacement levels of 10%, 20%, and 30%. The results indicated that PET incorporation reduces workability and density while increasing entrapped air content. Mechanical performance strongly depends on PET size and replacement level: a slight increase in the 28-day compressive strength was observed at 10% fine PET replacement, whereas higher substitution levels led to strength reductions of up to 31% and elastic modulus losses ranging from 4.5% to 34%, with more pronounced effects for coarse PET aggregates. In contrast, bulk density and thermal conductivity were significantly reduced by up to 15% and 42%, respectively, highlighting the potential of PET-based concretes for lightweight and thermally insulating applications. Microstructural analyses revealed a more porous and wider interfacial transition zone (ITZ) between PET aggregates and the cementitious matrix, which explains the strength degradation at higher replacement levels. In addition, strong correlations were established between physical and mechanical properties and UPV measurements, with R² ≈ 0.8-0.92 and low root mean square errors, enabling reliable nondestructive prediction of PET-based concrete performance. Overall, recycled PET aggregates provide a viable solution for producing lightweight concrete with improved thermal performance while contributing to plastic waste valorization, with PET particle size identified as a governing parameter controlling the balance between mechanical performance and functional properties.