This
study experimentally investigated the mechanism of deterioration for the bond between
CFRP plate and concrete
due to moisture attack. The debonding failure in the
concrete structures with externally bonded FRP has two major modes: cohesive
failure in the concrete surface layer and adhesive failure in the
interface between concrete and adhesive layer. A simple experimental approach was
developed in this study to directly measure the moisture condition in the
interface between concrete and adhesive layer with function of immersion
duration in water. Modified Double Cantilever Beam (MDCB) test was used to
measure the interfacial fracture energy for the CFRP plate debonding from
concrete substrate under Mode I loading. The MDCB specimens were submerged in
water for different periods before they were tested. When the value of
interface region relative humidity (IRRH) increased, fracture load and fracture
energy decreased and failure mode was also changed from cohesive failure to
adhesive failure. It was found that the residual thickness of concrete (RTC) on
the fracture surface was directly related to the relative humidity in the
interface region. When the IRRH was greater than 55%, the value of fracture
energy Gf began to decrease
significantly with the increase of the IRRH and immersion duration.