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

ABSTRACT

Glued-in Rods (GiR) connections are widely used in timber engineering as a connector between individual load-bearing 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-Fibre Reinforced 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-curing 2 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 Glued Laminated Timber (GLT), and inductively cured through the addition 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 67 large-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 as 1–10 days down to 10 min.

KEYWORDS:

• Glued-in Rods
• Curie particles
• accelerated curing
• electromagnetic induction
• inductive heating

Additional information

Funding

This work was financially supported by the Forschungsvereinigung Internationaler Verein für Technische Holzfragen e.V. (iVTH) program IGF- 19259N funded by the German Federal Ministry for Economic Affairs and Energy.