Evaluation of bond quality at the interface between steel bar and concrete using the small-dimension break-off test

This paper investigates the feasibility of using the small-dimension break-off test for evaluation of the bond quality at the interface between steel bar and concrete. Experimental studies were performed on bar-type concrete specimens and reinforced concrete beams. Twelve bar-type concrete specimens containing plain and deformed steel bars with different diameters were used to develop the relationship between the break-off moment and the adhesive strength at the steel bar/concrete interface. Subsequently, three reinforced concrete beams containing normal reinforcing bars, epoxy-coated reinforcing bars, and bars smeared with oil to simulate various adhesive conditions at the bar/concrete interface were used to study how the break-off moment and the bond strength were affected by the different adhesive conditions. In addition, two beam specimens containing normal reinforcing bars were vibrated severely on a self-made shaking table shortly after initial setting of concrete to simulate the bond damage in fresh reinforced concrete beams due to unexpected vibration or impact. Experimental results show that the effective break-off moment has a good correlation with the adhesive strength at the interface between steel bar and concrete. The break-off moment increases with an increase in bond strength. It is demonstrated that the small-dimension break-off test is capable of evaluating damage at the steel bar/concrete interface.