Composites and FRP-Strengthened Beams Subjected to Dry/Wet and Salt Fog Cycles

Carbon (CFRP) and glass (GFRP) fiber-reinforced composites of epoxy matrix are considered in the study, with greater emphasis on GFRP. Accelerated conditioning was imposed in the form of salt fog cycles, hygrothermal cycles (tap water), and tidal-like cycles (aqueous solution of NaCl, 50g/L), both on laminate composites and on beams externally reinforced with fiber-reinforced polymers (FRP) on their soffit. Freeze/thaw cycles were also applied to the study of degradation of the laminates. Mechanical tests showed degradation due to damage to the matrices, fiber-matrix linkage or bond between FRP and concrete. Several advanced techniques were used to interpret the results and enable better understanding of the phenomenological data. Changes on the glass transition temperature (Tg) of the epoxy matrix are reported as possible indicators of decrease of the tensile strength of the GFRP composite. Attention is given to the evolution of the relative values of the tensile strength of concrete and adhesive along time given their importance on the effectiveness of the FRP-adhesive-concrete joints. The results revealed, e.g.,that the more severe decrease of the carrying capacity of the beams was due to the salt fog cycles in the beams strengthened with CFRP.