Detection of Delamination in Concrete Slabs using Infrared Thermography and Impact Echo Techniques: A Comparative Experimental Study

Inspection of bridge decks is of primary importance in the field of bridges maintenance since, unless other structural components, they are more subjected to degradation and traffic-induced deterioration phenomena. Among the various deterioration mechanisms, delaminations are generally difficult to detect because no visible effects are usually observed on the deck surface. Since the entity of the damage progressively increase during time, methodologies able to effectively detect delaminations are needed in order to design appropriate solutions and reduce maintenance costs. In this work, the results obtained using two different nondestructive techniques, namely the impact echo (IE) method and the infrared thermography (IR), are compared. Experimental tests have been performed on a 20cm thick concrete slab containing delaminations of various extensions and on a small 60cmx60cmx20cm concrete specimen. Impact echo tests have been performed, with ultrasonic waveforms collected on an orthogonal grid of points spaced 30cm apart. Spacing was reduced to 5 cm for IE data collection in the small block. Leveraging different features extracted from IE, delaminations have been located. The results obtained using the impact echo test have been compared with those extracted using the infrared thermography. The main concept behind the use of the IR is that embedded horizontal interfaces behave as heat traps, resulting in different temperature areas on the slab surface. A discussion on the pro and cons of the two methodologies is provided and the paper ends with a preliminary attempt to perform data fusion, combining the results from the 2 different nondestructive techniques.