Experimental study on the bond strength and durability of FRP-timber laminate bonded joints

Fiber-reinforced polymer (FRP) composites offer high strength-to-weight ratios, while timber is an environmentally sustainable construction material. Hybrid FRP-timber (HFT) structural members combine the advantages of these two materials. Selecting an appropriate adhesive compatible with both FRP and timber and providing sufficient bond strength is crucial for HFT structural members. This study investigated four commercially available adhesives through tensile shear tests on 480 FRP-timber laminate single-lap joints, covering epoxy, bio-epoxy, phenolic resin, and polyurethane, glass and jute fibers, dry and aged conditions, and manufacturing pressures of 0.1, 1, and 2 MPa. At 1 MPa, aged glass FRP (GFRP)-timber laminate joints bonded with epoxy, bio-epoxy, phenolic resin, and polyurethane had mean bond strengths of 2.75, 3.17, 1.90, and 6.25 MPa, corresponding to reductions of 73.7%, 64.5%, 60.8%, and 35.4%, respectively, while the corresponding aged jute FRP (JFRP)-timber laminate joints exhibited reductions of 97.5%, 95.5%, 62.6%, and 83.4%, respectively. Although polyurethane provided the highest aged strength for both fiber types, the JFRP results were affected by FRP rupture in some dry groups and predominantly adhesion failure after aging. Overall, polyurethane showed the most favorable aged performance under the adopted severe comparative aging protocol, while adhesive selection should also consider fiber type, failure mode, manufacturing pressure, and exposure conditions.