Pre-applicable structural adhesives for timber engineering: Glued-in G-FRP rods

Adhesively bonded connections usually outperform traditional mechanical fasteners, as forexample dowels, screws of bolts. Among the most promising bonded joints commonly used intimber engineering, glued-in rods stand out for their capacity to achieve architecturallyappealing and yet mechanically performing connections [1]. Adhesively bonded connectionsrely upon a series of requirements to achieve adequate quality and performance; among themost critical are long curing times, minimum temperatures for curing, compliance with exactmixing ratios, and, in the case of glued-in rods, ensuring the complete filling of the borehole.The Fraunhofer IFAM has developed the so-called PASA technology (Pre ApplicableStructural Adhesive). These Adhesives allow a separation of the adhesive application and theactual joining process which can be carried out at different times and at different places [2].The example considered in this research was realized as a reactive hotmelt epoxy resin; it issolid and tack-free at room temperature and is applied in melted state at about 80 °C. Thesubsequent curing of the adhesive occurs at a considerably higher temperature (>120 °C), [3].In the research presented herein, G-FRP rods were coated with a PASA filled with metallicparticles, leading to a semi-finished product, subsequently inductively heated, and finallytested for strength. The study demonstrated that it is possible to separate the adhesiveapplication (which requires much care) from the application on site (which much lessstringent requirements), thus lowering the hurdles for practitioners to consider adhesives forstructural applications.