Bond strength of carbon fiber composites glued to concrete surface

This paper describes an analytical study about the bond between concrete and glued carbon fiber composites (CFCs) using data of 2 experimental researches. A total of 27 double compression‐tension tests were carried out on specimens with 2 concrete cubes (fixed and movable) connected by carbon fiber strips on opposite sides. The variables were concrete strength, with the evaluation of 9 specimens with strength of 20.5 to 38.1 MPa, with monotonic loading and smooth surface for all specimens, and 18 specimens with strength of 23.2 to 40.8 MPa, with monotonic loading and loading/unloading cycles and different concrete surfaces (smooth face and rough face). The test results showed that the ultimate bond stress slightly varies according to concrete strength in the analyzed zone. The strains of CFCs and concrete were measured, allowing the calculation of bond stress and the corresponding mean strain, which were compared with the values obtained by the expression given in the international codes. The prediction of the old expression applies to steel plates strengthening method, and the results of a more recent expression of CFC glued to concrete given by fib Bulletins and Model Code 2010 are compared with test results. The experimental results provided graphs and correlation curves for bond stress vs maximum strain, energy of fracture vs bond stress and a relationship between the mean shear strain and concrete strength. The expression for fracture energy given by fib Bulletins and Model Code 2010 varies with concrete strength fc and a reasonable agreement with test data was achieved.