Effects of corrosion on bond behavior between steel strand and concrete

An experimental program involving 12 pull-out specimens investigated the effects of corrosion on bond behavior between steel strand and concrete. The specimens were mixed with chloride and exposed to both indoor and outdoor natural climate to approximate the actual effects of corrosion. The specimens were corroded for 17 months until the widest corrosion crack reached 0.7 mm. The pull-out test results show that the bond–slip curve of the uncorroded strand consists of three segments, namely, ascending, approximate horizontal, and descending, whereas the curve of the corroded strand consists of only two segments, namely, ascending and descending. Additionally, the gradient of the descending segment of the curve of the corroded strand increases with the severity of corrosion. The bond strength of the corroded strand does not degenerate within the corrosion level. The pull-out process of the strand may be divided into four stages: elastic, strengthening, softening, and residual. Two comparisons revealed the effects of corrosion on strand bond behavior. Compared with ordinary corroded bars in terms of bond performance, the strand exhibited the largest critical crack width corresponding to the degradation of bond strength, the deformed bar exhibited the second-largest value, and the plain bar had the lowest value of 0 mm. Corrosion of the strand in a pre-tensioned prestressed concrete structure was found to degrade the tensile strength of the strand instead of its bond strength.