Experimental studies on void detection in concrete-filled steel tubes using ultrasound

Due to shrinkage and/or inadequate compaction during concreting, voids may develop in a concrete-filled steel tube (CFST) between the concrete core and outer steel tube, which reduce the confinement effect of the steel tube on the concrete core, and further, decrease the load-carrying capacity and ductility of a CFST. In this study, an ultrasonic technique is utilized for quantifying voids in CFSTs by analyzing the ultrasound travel time in them. Four potential travel paths are identified in CFSTs with/without pre-set voids. By making a comparison of the experimental and theoretical ultrasound travel time, the actual ultrasound travel path is determined in CFSTs. Further, by analyzing the matrix of ultrasound travel time obtained from experiment, a novel method is proposed to generate the chromatogram of the distribution of ultrasound travel time, which is utilized to quantify the voids in a CFST. The chromatogram intuitively shows the position and geometry of the voids in CFSTs and is in reasonable agreement with the pre-set voids. This study, therefore, establishes a new method for quantifying voids in a CFST through the ultrasonic technique.