Impact of sulfate attack on flexural behaviour of CFRP strengthened concrete beams

Abstract

The effect of exposing concrete beams (150 × 250 × 1600 mm), retrofitted with parabolic and straight profiles of near-surface-mounted (NSM) carbon-fibre-reinforced polymer (CFRP) ropes, to mild and moderate stages of cyclic sulfate treatment (CST) is investigated as a part of an ongoing comprehensive study. A total of 16 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 8690μ strain, respectively, were attained. Mechanical tests on concrete cylinders showed increased brittleness of concrete as a result of the CST, with 6% and 15% reductions in compressive strength after exposure to 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 were noticeably increased for those exposed to the moderate stage of CST, owing to the significant precompressive 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.