Title : Durability aspects of filled wood cracks with different types of adhesives and sealants
Abstract:
Oversized cracks in wood reduce the strength and stability of structures. Cracks can be mechanically stabilized (e.g. by steel fasteners) or can be filled with sealants. The aim of this work was to verify the durability of selected commercial adhesives and sealants. For this experiment, two wood adhesives (epoxy resin, polyurethane /PUR/ adhesive) and two sealants (MS polymer sealant, polyurethane sealant) were selected. The glued joints for the determination of shear compression strength using all the selected adhesives and sealants were prepared from spruce wood. Before the strength determination, the specimens were soaking in cold water (for 96 hours); and in boiling water (6 hours in boiling and 2 hours in cold 20°C water), after this treatment, the acclimatization as a reference sample was provided. Reference samples were stored at 20 °C and 65% relative humidity for one week. Moreover, the shear area was visually analysed and the percentage of adhesion failure at the interface of adhesive-wood was evaluated.
Significantly higher strengths were achieved with both representatives of the adhesives for reference samples; for PUR in an amount of 1.5 MPa and for epoxy resin 1.6 MPa. For epoxy adhesive, the adhesion failure of 85% and for PUR adhesive the failure of 70% was reached. The used sealants achieved too low strengths, for the MS polymer the lowest strength of 0.1 MPa was achieved after 96 hours in cold water, for the polyurethane sealant the lowest strength of 0.2 MPa was determined for reference. Almost 100% adhesion failures in all environments were achieved for both tested sealants. After exposure in boiling water, the highest decrease in strength was recorded for epoxy adhesive of almost 50% compared to the reference. A decrease in strength of 37% was recorded for the PUR adhesive. The strength behaviour of both the sealants reached almost the same values as the reference sealants.
For the epoxy resin, due to its low viscosity, the possibility of filling was verified. The tensile properties of non-filled reference and filled epoxy by different fillers were determined on dog bone samples (type 1B, according to EN ISO 527-2). As the fillers, cotton flakes (in the amount of 10% and 20% of resin) and spruce sawdust (in the amount of 10%, 20% and 30% of resin) were chosen. The maximum fibre length for cotton flakes is 0.5 mm and width 0.025 mm, for spruce sawdust the maximum particle size is 0.5 mm. The average values of tensile strengths for epoxy adhesive with fillers slightly decrease compared to the reference in all cases. The reference achieved strengths of 27,7 MPa. For epoxy filled with cotton flakes, the highest strength was 26.7 MPa at 10% fill, and for spruce sawdust 25.7 MPa at 20% fill.
