Impact of sulfate attack extent on the flexural behavior of CFRP-strengthened concrete beams

The effect of exposing concrete beams (150 × 250 ×1600 mm), retrofitted with parabolic and straight profiles of NSM carbon FRP ropes, to mild and moderate stages of cyclic sulfate treatment (CST), is investigated as a part of an ongoing comprehensive study. A total of sixteen beams were used to evaluate structural performance for strengthened beams before and after exposure to CST for about 4 and 11 months when free concrete expansions of about 2008 and 8690 μ strain were attained, respectively. Mechanical tests on concrete cylinders showed increased brittleness of concrete due to the CST with 6% and 15% reductions in compressive strength after exposure to the mild and moderate stages of CST, respectively. The load capacity and stiffness for beams exposed to the mild stage of CST were slightly decreased, yet experienced noticeable increases for those exposed to the moderate stage of CST, owing to the significant pre-compressive stresses induced in concrete. In contrast, rotational ductility and toughness were progressively decreased as the treatment progressed. Generally, concrete beams, strengthened with curved and straight NSM CFRP ropes, cannot retain their overall structural performance under moderate levels of sulfate attack.