Influence of moisture and thermal cycles in bonding of FRP laminates on timber elements

Durability of composite systems used as strengthening material in timber elements, is a topical issue, especially in the field of preservation and restoration of historical structures. The influence of moisture on the adhesion of composites, before and after application, as well as the effect of thermal exposure, are not clarified yet. Moreover, in the specific field of composites application, standards are still lacking. In the paper, several experimental procedures, both micro-structural and mechanical, are considered, to measure the effect of moisture and temperature, also combined. Carbon, glass and aramid textiles are applied with epoxy resins on timber samples. Pull-off tests were performed to preliminarily compare the ultimate loads and to check the failure modes. Then, optical microscopy allowed investigating the behavior at wood-FRP interface. Finally, IR spectrometry was used to identify possible modification in the matrix of the strengthening material due to the alteration of the two environmental factors