Hardwood rods glued into softwood using environmentally sustainable adhesives

Over the past years increased numbers of studies about the implementation of adhesive bonding in timber engineering were published. For instance efficient timber-timber, timber-glass and timber-steel connections, and structures, can be achieved using the adhesive bonding technology. Previous research [1] indicated that connections with Glued-in Rods (GiR) have the potential to transfer high loads. Two-component Epoxies (EP) and Polyurethanes (PUR) are the most used adhesives to glue rods typically made of threaded steel bars or rods made of fibre reinforces polymer (FRP) into timber. An alternative possibility [2], in line with current environmental concerns and questions of sustainability, investigates the possibility of GiR made of hardwood dowels. This research dealt with experimental investigations carried out with different geometric parameters, in which beech (a hardwood) rods are glued into spruce (a softwood) blocks. Adhesion was achieved using a series of ecological adhesives, and results are compared to a series of commonly used chemical-based adhesives. The presentation of the results is completed by the numerical modelling of the considered samples, including a methodology to predict the joint capacities.