Hardwood rods glued into softwood using environmentally sustainable adhesives

ABSTRACT

Over the past years, a large number of studies about the implementation of adhesive bonding in timber engineering were published. Current practice is to use two-component (2K) epoxies and polyurethanes in conjunction with threaded steel bars, reinforced concrete bars, and rods made of fibre reinforced polymer. All these material might be considered questionable in terms of sustainable ecology. The current article investigates the possible substitution of aforementioned metallic bars by hardwood dowels, and the polymer-based adhesives by glutine- and casein-based ones. It summarises experimental investigations carried out with different geometric parameters, in which beech (a hardwood) rods were glued into spruce (a softwood) blocks. Joint capacities achieved using glutine- and casein-based adhesives were compared with results using 2K epoxies and 2K polyurethane adhesives under dry conditions, and under the influence of moisture. Results indicate that current glutine and casein adhesives, if used under dry conditions, achieve similar strength; however, the influence of moisture is still a limiting factor that severely restricts their usage under adverse conditions. The presentation of the results is completed by a numerical modelling of the considered joints, including a methodology to predict their capacity with a reasonable degree of accuracy.

KEYWORDS:

• Adhesives for wood
• biodegradable adhesives
• glued-in rods
• environmental issues
• finite element analysis
• timber engineering

Acknowledgement

The authors wish to acknowledge the following companies for providing technical support and free samples of the adhesives used in this study: Fritz Häcker GmbH + Co. KG, Türmerleim GmbH, Ulrich Lübbert Warenhandel GmbH & Co. KG, and Henkel & Cie. AG.