Moisture and Temperature Influence on Biocomposites-to-Timber Bonding

Compatibility and durability are fundamental aspects to take into account when dealing with strengthening and repair of structural components in existing buildings. In particular, timber elements in floors and roofs, like beams and joists, can be improved in their load-bearing capacity by the use of composite (fiber-reinforced) materials. Applied as textiles or laminates, those materials can provide additional tensile strength without weight increase, and are easily applied in situ. Recently, an increasing interest towards the biocomposites (flax, hemp) opened new perspectives: the advantages in comparison with traditional FRPs includes the higher mechanical compatibility and sustainability, especially if glues suitable for wood (e.g., vinyl) are used as matrix, instead of epoxy resins. In the paper, the results of an experimental campaign carried out at the University of Padua, aimed at investigating the influence of humidity and temperature on the adhesion of composite materials (carbon or glass FRP) and biocomposites (flax) reinforcing spruce timber elements are presented. Epoxy resins were used as matrix for all composites; flax was also applied with vinyl glue and considering a protective treatment (alkaline-based). Effectiveness of bond at the interface timber-reinforcement was measured by pull-off tests, and analyzed at microstructural level by optical microscopy and infrared spectroscopy