Date of Award

Spring 5-2023

Document Type


Degree Name

Doctor of Philosophy (PhD)


Micro and Nanoscale Systems

First Advisor

Arun Jaganathan


Concrete pipes constitute an integral part of the buried infrastructure, and non-destructive testing (NDT) plays an important role in their maintenance effort. Impact echo (IE) is a well-established NDT technique that is widely used for the investigation of concrete structures. In this technique, the thickness (or resonant) frequency is first measured by inducing (compression) P-wave into the structure using an impact source and recording the elastic wave generated using an accelerometer. From the knowledge of P-wave velocity of the medium, the unknown thickness and subsurface defects are then established. To effectively apply this technique, the transducer should be properly coupled with the surface. However, this often becomes a difficult task due to the poor surface quality of concrete. Alternatively, instead of capturing the elastic wave with a contact-based transducer the leaky acoustic wave that accompany the elastic wave is captured with a microphone and the thickness frequency is calculated. This non-contact variation of IE is called the air-coupled IE (ACIE) and it has been shown to be effective for testing plate like concrete structures (e.g., pavements and bride decks). In this dissertation, the feasibility of ACIE for the NDT of buried concrete pipe is investigated. The investigations are conducted in two stages. First, numerical modelling is conducted to test the effectiveness in pipes and then experimental validations are conducted. A structural-acoustic coupled finite element model is created using the COMSOL Multiphysics software, and the propagation of elastic and acoustic waves in a fluid-filled concrete pipe is simulated for standalone and buried pipe. The effectiveness of ACIE is studied when a pipe is surrounded by soil. Two types of soil surrounding the pipe studied to learn more about the quality of the data that might be anticipated from ACIE technique inside the pipe. Using these models, various aspects of ACIE are studied and its performance against the conventional IE is compared. Following the numerical verifications, two laboratory tests setups are constructed with a standalone and buried reinforced concrete pipes (RCP) and ACIE is demonstrated using them. The (unknown) wall thickness is calculated in each case and the results are compared against the conventional contact-based technique. While the presence of soil caused energy losses which affected the amplitude of acoustic wave, it was enough to be detected with good signal to noise ratio.

Several enhancements to improve the performance of this technique are studied. For instance, a way to improve the signal-to noise ratio of the acoustic signal is investigated using noise suppressers. For rapid implementation of technique and fast data gathering a semi-automated ACIE setup is also developed. Finally, the ability of the technique to detect several commonly occurring problems in a concrete pipe is investigated.

In summary, ACIE technique shows promising results for buried pipe testing.