Effect of Recycled Pet-GFRP Hybrid Laminates on the Ultimate Moment Capacity of Reinforced Concrete Beams
DOI:
https://doi.org/10.63746/njtd.v23i2.4716Keywords:
PET-GFRP hybrid laminates, moment capacity, stacking sequence, recycled PET-FRP, ductility index, sustainable retrofittingAbstract
Reinforced concrete (RC) structures increasingly require strengthening due to ageing, deterioration, and higher service demands. Conventional glass fibre-reinforced polymer (GFRP) strengthening systems effectively improve flexural strength but exhibit brittle failure and limited deformation capacity, while sustainable alternatives capable of balancing strength and ductility remain insufficiently investigated. The objective of this study was to evaluate the influence of recycled polyethylene terephthalate fibre-reinforced polymer (PET-FRP) and GFRP hybrid laminate configurations and stacking sequence on the flexural performance of RC beams. Ten under-reinforced RC beams (150 × 250 × 1200 mm) were cast using C30 concrete and divided into five groups comprising an unstrengthen control, PET-FRP, GFRP, PET-GFRP-PET, and GFRP-PET-GFRP strengthening configurations. Tensile coupon tests were conducted to determine the mechanical properties of the laminates before they were externally bonded to the beam soffits using Sikadur®-30 epoxy through the wet lay-up technique. All specimens were tested under four-point monotonic bending, and load-deflection response, ultimate moment capacity, displacement ductility, strain development, and failure modes were evaluated. The GFRP-PET-GFRP hybrid configuration achieved the highest ultimate moment capacity of 38.57 kN·m, representing a 57.6% increase over the control beam, while the PET-GFRP-PET hybrid attained 36.67 kN·m with superior hybrid ductility (? = 3.36). PET-FRP-only beams exhibited the greatest ductility (? = 3.96), whereas GFRP-only beams showed the lowest ductility because of brittle fibre rupture. Both hybrid laminates exhibited progressive failure mechanisms that enhanced structural performance compared with the single-material systems. These findings demonstrate that recycled PET-GFRP hybrid laminates provide an effective and sustainable strengthening solution for RC beams. The GFRP-PET-GFRP configuration is recommended where maximum flexural strength is required, whereas the PET-GFRP-PET configuration is more suitable for applications requiring greater deformation capacity.
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