The civil engineering sector in Europe has been experiencing an increase in utilisation of natural materials for construction of both family and multi-story buildings. This is supported in part by ambitious policies like “Fit for 55” where the use of bio-based, biodegradable, and regionally produced materials and products within the EU are of great importance. Among these materials, wood plays a significant role due to its advantageous mechanical and thermal properties with respect to its weight, and due to its positive environmental impacts. However, with changes in climate come changes in the forest composition. The forests in Central Europe are currently transitioning towards more broadleaved species like European beech (Fagus sp.). Beech and other hardwood species are foreseen to play a significant role in the future of construction. However, when creating engineered wood products (EWP) and large timber structures, connections must be used to provide the needed structural dimensions and spans seen in products like cross-laminated timber (CLT) and glued laminated timber (GLT). Adhesive bonding is the most common connection to form EWP and plays a significant role in the performance of the entire product, especially from a long-term perspective during service life and ageing. Long-term service life means that EWPs for indoor/outdoor exposures face damaging elements causing undesired phenomena such as aesthetic weathering, fatigue, delamination, or failures at bond lines. The exposure is represented by a combination of periodic hygro-thermo-mechanical loads that vary based on season, precipitation rate, wind speed, UV radiation, drying elements such as air-conditioning, location, etc. These natural and human-caused conditions heavily impact performance of all timber structures, but is of great concern when critical structural elements like CLT or GLT are used in structures like bridges, towers, tall-timber buildings, lookout towers etc. The loads do not impact only the wood material itself but also the adhesive bond that binds the wooden phase. To extend the durability of adhesive bonds and to predict their service life or failure, understanding of its behaviour with respect to environmental conditions must be provided. To achieve these goals, new approaches and techniques are necessary to be used to obtain higher quality bond lines for realistic, complex loadings. Prediction and diagnostics models would help to lower production costs of adhesively bonded timber structures due to detailed knowledge of their behaviour and response to normal service life impacts. Despite the ever-growing proportion of timber structures in the Central European region, there is a lack of knowledge about the impact that complex loads and service conditions have on the bond performance of beech EWPs. The DIAMONDS project aims to address this knowledge gap by carrying out research on the impact of ageing on rigid (PUR) and flexible polyurethane (FPU) bonds in beech EWPs to be used in timber constructions. This is a bilateral project between Poland and Slovenia that is led by the Cracow University of Technology. The other partners are the AGH University of Science and Technology (Poland), InnoRenew CoE (Slovenia), and the Slovenian National Building and Civil Engineering Institute. The project’s objective is to understand how the ageing of rigid and flexible PUR-beech bonds in timber structures affects physical performance.
Keywords: adhesive, engineered wood products, flexible, polyurethane
Authors
Matthew Schwarzkopf
InnoRenew CoE and University of Primorska, Slovenia
Jaka Pečnik
InnoRenew CoE and University of Primorska, Slovenia
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