Evaluating the bond-loss of reinforcing bar in new concrete construction subjected to earthquake using the impact-echo method

The purpose of this paper is to develop a non-destructive test method fur evaluating the bond condition of reinforcing bars that were damaged by the earthquake while they were still cast in the form. In the experimental design, different degrees of damage to the steel-concrete interfaces were successfully created when the specimens were subjected to a single-frequency motion that induced a resonant vibration of the steel bar exposed outside of the specimen. Due to proper confinement, the failure mode for most of the specimens was pullout mode. The local bond-loss of the steel bars was evaluated by both non-destructive impact-echo tests and the destructive pullout tests. Bad bonds can be quantitatively determined by the peak amplitude corresponding to the steel bar in the simulated transfer function derived from the displacement waveform of the impact-echo tests. The empirical formula describing, the relation between the average steel amplitude in the impact-echo response and the loss of bond stress is established for further practical applications.