A comparative study on the mechanical properties of sandwich beams made with PET FRP facings and varied recycled PET cores

The objective of this paper is to assess the mechanical performance of new forms of sandwich beams predominantly comprised of recycled plastic polymers. These beams feature two types of polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) facings: one with a bio-resin matrix and the other with a partial bio-resin matrix. The core of the beams is a focal point of the study as well, comprised of recycled PET (R-PET). Fifteen different types of sandwich beams were tested, with three identical specimens from each type, totaling 45 beams. Each beam, measuring 240 mm in length, was fabricated and categorized based on its core composition: either an R-PET honeycomb or an R-PET foam core. The study investigated key parameters including the core type (honeycomb or foam), core thickness (12 mm or 15 mm), core orientation, and facing thicknesses (1 mm or 2 mm). The mechanical testing of these beams involved a four-point bending setup to assess their flexural performance. This included analyzing mid-span load-deflection, moment-curvature behaviours, and changes in tension and compression strains in the facings during bending. The results demonstrated that core density, type, and facing thickness significantly impact the beams' stability and failure modes. High-density foam cores primarily failed through core shear, while lower density cores showed both core shear and wrinkling, dependent on facing thickness and core type, highlighting the complex influence of material properties on structural behaviour. A finite element (FE) model was developed to verify the experimental findings, effectively corroborating the test results. The research data is intended as a reference for structural designers seeking to incorporate sustainable alternatives into traditional building materials, thereby promoting a more environmentally conscious approach within the construction industry.