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.