Adhesive properties of laminated veneer lumber poles for use in temporary soil nailing: bonding performance of curved structures in a high-alkaline environment
Circular hollow sections of beech-laminated veneer lumber (LVL) for the use as temporary geotechnical soil nailing systems are currently being developed. Due to their permanent subsoil cement embedment, investigations of the bond line quality of the timber sections are essential. This paper presents the bonding properties of flat and curved beech LVL after cyclic conditioning in a water–cement grout solution aimed at inducing short- and long-term alkaline attack of the timber. In total, 409 and 69 samples were tested in tensile shear tests after short-term and long-term conditioning, respectively. Three different adhesive systems, a one-component polyurethane adhesive, a melamine–urea–formaldehyde adhesive and a melamine–urea–formaldehyde adhesive modified by means of (polyvinyl)-acetate adhesive were investigated and compared. Short-term conditioning by submersion in boiling cement suspension was found to be a reliable method for testing the bonding performance rather than long-term conditioning. In the case of tensile shear tests of samples subjected to long-term treatment, wood material strength was the decisive criterion. Generally, tensile shear test samples of all investigated adhesives achieved reliable bonding for a pressing force up to 1.0 MPa. No relationship was recognised between the determined bonding failure and the wood properties tensile shear strength, wood failure percentage, fracture pattern and bulk density of veneers adjacent to the bond line. For the determination of the bond line integrity of curved veneer poles, it was necessary to test bonding quality in a combined test using curved and flat samples and to compare tensile shear strength with data determined on reference samples in the same veneer population without bond line.
The authors would like to thank Mr. Alexander Englberger for his great efforts carrying out the tests and Dr. Christian Lehringer (Purbond AG) for providing adhesive and knowledge. The research was supported by the German Federal Ministry of Education and Research, Grant Number 13FH022IX4.
- EN 13017–2 (2001) Solid wood panels—classification by surface appearance—part 2: hardwood. European Committee for Standardization, BrusselsGoogle Scholar
- EN 302–1 (2013) Adhesives for load-bearing timber structures—test methods—part 1: determination of longitudinal tensile shear strength. European Committee for Standardization, BrusselsGoogle Scholar
- EN 635–2 (1995) Plywood—classification by surface appearance—part 2: hardwood. European Committee for Standardization, BrusselsGoogle Scholar
- EUROSTAT (2017) Eurostat regional yearbook, 2017th edn. Eurostat statistical books. Publications Office of the European Union, LuxembourgGoogle Scholar
- FprCEN/TS 16637-3 (2015) Construction products—assessment of release of dangerous substances—part 3: horizontal up-flow percolation test. European Committee for Standardization, BrusselsGoogle Scholar
- Horioka K, Gamoh M (1973) The mechanism and durability of adhesion in wood-glue bonds. In: Proceedings of the IUFRO. Division 5 forest products, IUFRO-5 meeting, pp 508–527Google Scholar
- Kollmann F (1951) Technologie des Holzes und der Holzwerkstoffe (Technology of wood and wood-based materials). 1 Bd.: Anatomie und Pathologie, Chemie, Physik, Elastizität und Festigkeit (Volume 1: Anatomy and pathology, chemistry, physics, elasticity and strength), 2nd revised and extended edition. Springer, BerlinGoogle Scholar
- prEN 14374 (2016) Timber structures—laminated veneer lumber (LVL)—requirements. European Committee for Standardization, BrusselsGoogle Scholar
- Schmidt M (2014) Die Verklebung von Buchenholz für tragende Holzbauteile unter besonderer Berücksichtigung der Farbverkernung (Bonding beech wood for load-bearing timber structures with particular consideration of coloured cores). Dissertation, Technische Universität MünchenGoogle Scholar
- Wagenführ A (ed) (2012) Taschenbuch der Holztechnik: (Paperback of wood technology), 2nd edn. Carl-Hanser-Verlag, MünchenGoogle Scholar