Production feasibility and performance of carbon fibre reinforced glulam beams manufactured with polyurethane adhesive

Wood is a structural material traditional and modern at the same time. It can be used as solid timber or combined with adhesives to form engineered wood products with enhanced mechanical properties, opening several opportunities for the development of the wood building sector in the construction industry. Here, the feasibility of producing glulam beams reinforced with carbon fabric applied using mono-component polyurethane glue was analysed. The same adhesive was utilized during beam manufacturing; thus, carbon-reinforced elements were produced with a unique assembling procedure. Unreinforced glulam beams were compared with strengthened elements; the factors analysed were the thickness of the carbon fabric and the adhesive type used at the fabric-timber interface, comparing the polyurethane adhesive with an epoxy resin. Both bending tests and numerical modelling have been performed in the study. Tests showed that the general performance of the strengthened elements with polyurethane glue, in terms of strength and stiffness, was equivalent with the one obtained with the epoxy adhesive used as a reference, thus confirming that polyurethane can be fully suitable and efficient for industrial production. The carbon fabric considerably improved the bending strength of the original element (between 45% and 57%); the quantity of fibres did not influence the strength, but it significantly affected the stiffness (increased from 12% to 22% for carbon fabric of 500 and 1000 g/m2 weight, respectively, compared to unreinforced beams). The modelling evidenced that the effective modulus of elasticity of the reinforcement, as a system of carbon fabric and adhesive, was on average higher and with lower variability for the specimens with polyurethane adhesive compared to the ones with the same carbon fibre quantity but glued with epoxy resins.