Bond degradation of rebar and concrete confined with corroded stirrups: effects of concrete grade and casting position

An experimental study was conducted to investigate the effects of stirrup corrosion, concrete strength and casting position on the behaviour of the bond between steel bars and concrete. Accelerated corrosion was applied to corrode the stirrups in concrete specimens under laboratory conditions. In total, 180 specimens were cast and tested in this experiment. The specimens had three nominal concrete strengths of C20, C40 and C50 with two deformed steel bars of 18 mm in diameter set in a 200 × 200 mm diagonal concrete prism with two stirrups of 8 mm in diameter to provide confinement. The steel bars were cast with different pouring positions, namely the upper and lower ends. Five corrosion levels were investigated, namely 0, 5, 10, 15 and 20%; 12 specimens were investigated for each corrosion level. A pull-out test was carried out to obtain the bond–slip curves. The test results indicate that the porosity of concrete has a great effect on bond degradation with the increase of the steel corrosion level.