Durability of CFRP-concrete bond under sustained load in harsh environment

Carbon Fibre Reinforced Polymer (CFRP) has great potential in civil engineering applications. It is used extensively in extending the structural capacity or service life of aging structures. CFRP is one of the best alternatives to traditional retrofitting materials. It has a very high strength-to-weight ratio with good resistance to environmental effects. Together with the fibres, the adhesive and the substratum are the main constituents of the CFRP bonding systems. However, with high quality plated CFRP, the latter two components introduce some doubts about the system’s performance. There is therefore a crucial research need to investigate the effects of environmental exposures on the system under loading conditions. In the present work, the effects of extreme environmental exposures on the bond properties between externally-applied carbon fibre reinforced polymer (CFRP) and concrete were investigated. Preloaded CFRP-concrete samples at various load intensities were exposed to several conditions. The exposure conditions were temperature cycles with humidity, constant temperature at increasing humidity, soaking in saline water at different temperatures, and different salt concentrations. Finally, actual extreme marine site environments including direct exposure to sunlight were explored. The change of bond characteristics between the externally-applied CFRP and concrete due to permanent loads, aging, and exposure conditions were used as measures of degradation effects. Other properties such as the development of the strain field with load, bond-slip relationships, detection of cracking intensity and location were evaluated using photogrammetry and acoustic emission techniques. Tensile pull-out and torsional shear strength were also explored. A Neural Network method was implemented for the prediction of bond strength and the expected failure of preloaded samples in different environments. The objective of the study was to understand the behaviour of preloaded concrete-CFRP bonding systems and evaluate the changes in the bond properties due to combinations of factors in harsh environments. It was found that high temperature and the combined aggressive site conditions were the major factors leading to sample failure.