Ultrasonic Guided Waves Technique For Nondestructive Testing On Interface Delamination Of Reinforced Concrete

Reinforced concrete (RC) is universally used in the field of civil engineering for many virtues, inexpensive, high strength and thermal compatibility. However, the interfaces between concrete and rebar always delaminate because corrosion and fatigue loads impact, these factors shorten the service life of integral structure and lead to earlier failure prior to the designed period. The maintenance backlog will worsen as bridges age and costs rise. Thus, there is a urgent need for an effective and reliable nondestructive testing technique. The areas that investigated in this study are presented as follows.First, propagation principles and characteristics of ultrasonic guided waves (UGW) were studied, as well as factors that would put impacts on this. Then dispersion curves were plotted by numerical calculation, optimization of excited signals was explored and an ultrasonic experiment setup was designed to conduct experiments. Different data processing methods were also studied to get a more precise result. The result showed fast Fourier transform (FFT) is suitable for signals that collected in this study.Second, the impacts of stress level, temperature and strength were explored and an innovative algorithm was introduced to eliminate the dispersion. According to acoustoelasticity wave velocity varies as the stress level changes, but the calculation results showed that the wave velocity variation appropriates with length change. This means the stress puts on very little impact on detection. Both group velocity and amplitude of longitudinal modes are not very sensitive with temperature variations, while higher strength will lead to lower amplitude of peak-to-peak value.Third, specimens with different delamination defects were fabricated and tested to investigate the impact resulting from interface delamination. Time domain and frequency domain analysis were used to process received signals. In order to get a more precise result, energy attenuation parameter was proposed and a linear relationship was obtained.This study shows that interface condition in RC can be well evaluated by selecting proper excited signals and modes. Stress, temperature and design strength of concrete have little effect on the detection precision. This research successful proved UGW is an effective and reliable tool in nondestructive testing (NDT) of RC structures and provided solid foundations for future research of this technique.