Evaluating bond quality at steel/concrete interfaces using the normalized impact-echo spectrum

Abstract

The objective of this paper is to develop a nondestructive test technique based on stress wave propagation for evaluating the bond quality of concrete structures strengthened by externally bonded steel plates. In this paper, a newly developed technique based on the normalized impact-echo spectrum was used to quantitatively detect the size of air voids at the interfacial epoxy layer between steel plate and concrete. Experimental results show that in the normalized impact-echo spectra, the amplitude of the peak at the frequency corresponding to the wave reflections at the steel/epoxy interface increases with an increase in the air void size. The bond strength decreases with an increase in the peak amplitude due to the increasing size of the flaw.