Experimental investigation of the flexural and compressive behavior of LVL beams manufactured from poplar veneer waste reinforced with GFRP fabrics and rebars

Introduction: In recent decades, engineered wood products such as Laminated Veneer Lumber (LVL) have gained significant prominence in the construction industry owing to their uniform mechanical properties, engineered design capability, and reduced influence of natural wood defects. Despite these technical advantages, the production of LVL and other engineered laminated beams is associated with challenges including high consumption of premium raw materials and the generation of substantial volumes of wood waste during peeling, layering, and edging operations. Studies have indicated that between 15% and 30% of the initial wood volume remains as unusable waste. This waste holds particular significance in fast-growing species such as poplar due to their low density, limited dimensional stability, and susceptibility to natural defects. Accordingly, the present study was conducted to evaluate the feasibility of manufacturing large cross-section LVL beams from poplar veneer edging and layering waste, and to investigate the effect of reinforcement with fabric and GFRP rebars on the mechanical properties and failure modes of these beams. It is anticipated that the findings of this research will provide a practical solution for wood waste recycling while contributing to the advancement of technical knowledge in the field of reinforced engineered wood beams and promoting their broader application in sustainable structures.
Method: The layers of poplar wood (Populus deltoides) were supplied from the waste of a veneer and plywood factory in Neyshabur, Iran. The layers were cut to dimensions of 500 x 2 mm (length and thickness, respectively) and a minimum width of 250 mm. In the process of manufacturing LVL panels, urea-formaldehyde adhesive with 60% solids (Samad Company) was used. After telescoping, LVL panels of dimensions of 450 x 2 mm and different widths (minimum width 250 mm) were prepared. In order to produce beams with larger dimensions, four LVL blocks with a cross-section of 20 x 20 mm and a length of 450 mm were placed next to each other, and beams with a square cross-section of 40 x 40 mm and a length of 450 mm were made. The connection of the four small beams was such that in each treatment, adjacent beams were connected to each other from the sides only with epoxy adhesive, while on the facing surfaces of the beams, in addition to epoxy adhesive, a reinforcing agent was also used. In the glass fiber reinforcement treatment, a layer of GFRP fabric was placed continuously across the entire mid-section, while in the composite rebar reinforcement treatment, two 6 mm diameter GFRP rebars were placed in pre-installed grooves and after being impregnated with epoxy adhesive, the opposing beams were connected to each other in pairs. Flexural and compressive strength tests were performed in accordance with EN 408 standard.
Results: The results of the bending test showed that reinforcement with GFRP fabric and GFRP rebar increased the flexural strength by 11% and 19%, respectively, compared to the control sample. Also, changing the fabric from unidirectional to bidirectional reduced flexural strength by 26%, which indicates the decisive role of fiber orientation in the path of flexural stresses. The modulus of elasticity was also improved by about 11% and 19% in the samples reinforced with GFRP fabric and GFRP rebar, respectively. Overall, one-way fabric showed better performance than bidirectional type and GFRP ribbed rebar showed better performance than flat type. In the parallel compressive strength test of the fibers, reinforcement with GFRP fabric and GFRP rebar increased by 17% and 33%, respectively, compared to the control sample. These results show that GFRP rebars, especially the ribbed type, have a more significant effect on improving both flexural and compressive properties.
Conclusion: This study clearly demonstrated that poplar wood peeling waste has high potential for producing LVL with acceptable performance and reinforcement with GFRP composites can significantly enhance the mechanical properties of this product. The best performance was observed in samples reinforced with GFRP ribbed rebar, which provided a 19% increase in flexural strength and 33% in compressive strength. According to the findings, the use of unidirectional fabric and GFRP ribbed rebars for structural applications of this type of LVLs is recommended. This approach can be an effective step towards recycling wood waste and producing high value-added products in the wood-polymer composites industry.