Structural Behavior of Adhesively Bonded High Density Polyethylene Composite Beams

Finding a sustainable and structural material for the civil infrastructure domain, while remaining financially feasible, is a challenge for engineers. Recycled Plastic Lumber (RPL) is identified as an excellent sustainable material used by the construction industry in non-load bearing applications. There is a demand and an opportunity to resolve the aforementioned challenge by migrating RPL into structural applications. Although RPL has significant sustainable and structural advantages, such as light weight, low cost and high resistance to environmental degradation, its usability in the civil infrastructure applications is still at its early stages due to a lack of design guidelines. Furthermore, due to the brittleness of the RPL material, joining RPL components impose another challenge for engineers. Recently, however, many structural industries have considered adhesive binding as an excellent candidate for replacing the traditional joining methods (e.g. bolting and riveting) for joining load-bearing components, especially for scenarios involving joining brittle materials such RPL. The attractiveness of adhesives stems from their unique combinations of properties, which include: high strength, light weight, dimensional stability, high resistance to environmental degradation and ease of use. Due to these unique characteristics and advantages, the use of adhesive joints is on the rise in structural applications. On the other hand, the traditional bolted joint methods have gone a long way in creating appropriate technologies and gained years of design experience, which cannot be easily replaced. Accordingly, switching from traditional joining methods to adhesive bonding in civil infrastructure applications requires a large investment to establish a level of understanding comparable to that associated with traditional joining methods. In particular, it is crucial to characterize and fully understand bonded joint behaviors, strength and failure properties, and to be able to predict them for given geometries and loads. This research addresses both challenges by providing design guidelines for utilizing RPL in load-bearing structural application and by fully characterizing the behavior of adhesively bonded RPL joints. For addressing the first challenge, this research covers structural and sustainability assessments of an RPL beam. Experimental and numerical results of the four-point bending structural assessment of RPL beams reinforced with Glass Fiber Reinforced Polymer (GFRP) indicate that as the amount of GFRP reinforcement area increases, the stiffness of the RPL increases up to four times linearly The results also indicate that optimizing the beam section by using an I-shape beam or a hollow beam can reduce the weight and increase the surface area, improving the heat treatment process while maintaining 90%-95% of the beam stiffness. Results of the three pillars of the sustainability assessment (environmental, economic and social) show that reinforced recycled plastic beams have great environmental benefits compared to other structural materials, such as the reinforced concrete and the wood beams. For addressing the second challenge, this research covers the following: i) investigating the behavior of structural adhesives by characterizing their mechanical properties, ii) investigating the failure limits and failure modes of structural adhesives and iii) establishing a representative material model that can mimic their behavior and can be used in numerical models for computational studies. Comparison between experimental results and numerical results obtained from 3D finite element analysis show that the produced material model does mimic the actual behavior of the adhesive material at the bulk level and the interface level.