Multi-scale characterization of moisture and thermal cycle effects on composite-to-timber strengthening

• Use of vinyl glue for the application of natural (flax) textiles on timber elements.
• Multi-scale experimental study on flax applied to timber.
• Extensive study of flax-to-timber bond (pull-off, shear, microstructural analyses).
• Proposal of procedures for the study of durability of composites applied to timber.
• Comparison of flax and carbon fibers performance for timber strengthening.

The paper examines the influence of moisture and temperature cycles on timber elements reinforced with a wet lay-up system composed of various fibrous materials (carbon, flax) and matrices (epoxy resin, vinyl glue). A multi-scale experimental approach was adopted, including: (i) mechanical characterization of the composite reinforcement systems; (ii) investigation of behavior at the composite-to-timber interface by mechanical bond tests and microstructural analyses; (iii) four-point bending tests on strengthened timber beams. The results highlighted the good performance of natural-fiber composites compared with synthetic ones, and the marked influence of wood moisture content and temperature on bonding.