Field detection study of the bonding interface bubble defects in the full scale CRTS III slab ballastless track structure

The authors conducted a study on the efficacy of non-destructive testing methods to identify potential bubble defects at the bonding interface, which were a result of the field infusion process in the CRTS III (China Rail Track System III) slab ballastless track structure. Traditionally, these defects were detected through direct observation by the method of on-site uncovering slab. To expedite and enhance the detection of these bubble defects at the bonding interface, the authors were able to obtain fast and effective results via using the impact-echo method. Meanwhile, finite element models were used to construct different scenarios and the presence of the bubble defect would alter the propagation of stress waves inside the structure. Field experiments had shown that when the bonding interface was effectively bonded, the spectra displayed a peak echo signal of maximum amplitude, typically at a frequency ranging between 7000 and 8000 Hz. When bubble defects were present, the peak amplitude of the echo signal would shift to a frequency of around 12,000 Hz on the spectra. The presence of bubble defects at the bonding interface resulted in a rightward shift of the peak amplitude of the echo signal on the spectra.