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Accelerated curing of G-FRP rods glued into timber by means of inductive heating using Curie-particles - large-scale experiments at room temperature

: Voß, Morten; Vallée, Till


Journal of Adhesion (2020), Online First, 27 pp.
ISSN: 0021-8464
ISSN: 1545-5823
Journal Article
Fraunhofer IFAM ()

Glued-in Rods (GiR) connections are widely used in timber engineering as a connector between individual loadbearing members. Typically, GiR consist of a rod, e.g. rebars or threaded rods, glued into timber-based elements. However, rods made of new materials, as Glass-FibreReinforced Polymers (G-FRP) are increasingly being used due to their advantageous material properties like high tensile strength and good resistance against corrosion or chemical media. The cure of usually used and commercially available adhesives for GiR applications, mostly cold-curing2 K-epoxies (2 K-EPX) and 2 K-polyurethanes (2 K-PUR), is time consuming. After adhesive application, the components must be fixed and maintained in position from several hours to days before the connection can be stressed. This process, depending on the connection type, can be significantly time, and cost, consuming for contractors, which makes the process difficult on-site. In order to overcome these restrictions, the present study investigated accelerated curing with the help of Curie-Particles (CP)exposed to a high-frequency (HF) alternating electromagnetic field (EMF). The CP are added to the 2 K adhesives, the resulting mix is then exposed to the EMF, generating thermal energy, which in turn accelerates the chemical reaction and associated adhesive curing. Due to the very nature of the CP, heating proceeds until their Curie temperature is reached, at which point the heating automatically stops. As a result, accelerated curing is achieved independently of external monitoring. In the present study, G-FRP rods were glued into blocks of spruce GluedLaminated Timber (GLT), and inductively cured through theaddition of 33.3 w/w-% of CP. In total, four commercially available adhesives (three 2 K-EPX, and one 2 K-PUR) were investigated. The authors demonstrated on a total of 67large-scale GiR specimens that inductively heated specimens achieved almost identical failure loads, and fracture patterns (wood failure), compared to cold-cured references accompanied by a reduction of curing time from as long as1–10 days down to 10 min.