Concrete bridge deck overlay assessment using ultrasonic tomography

Infrastructure continues to age, which calls for inspections and repairs to ensure public safety. However, there are difficulties when it comes to structural monitoring of bridges and other structures. This is especially true for bridge decks with overlays as the deck substrate is not visible and existing inspection methods can be imprecise. Recent developments in nondestructive testing technology have opened the door for innovative inspection methods for infrastructure. One such technology is ultrasound evaluation, specifically in the form of linear arrays. One Ultrasonic Tomography Device (UTD), called MIRA, which implements this technology was deployed on a bridge deck to explore its capabilities with respect to assessing the internal condition of a deck with an existing overlay present. To achieve this objective, a 65-year-old bridge deck was selected for the ultrasound evaluation. Five locations with various overlay and deck conditions were scanned. The results indicated that when the overlay and the concrete deck are in good condition, the UTD could effectively detect the location and size of the top layer rebar and the deck thickness. It was also found that although the UTD scans showed a large area near the bottom of the deck (about 575 mm below the surface), it could not clearly decipher between the bottom surface of the deck and the bottom layer reinforcement. In addition, when visible cracks exist in the overlay, the UTD scans cannot clearly show the rebar details and deck thickness. The results indicate potential for determining the extent of bridge deck deterioration for the purposes of maintenance and rehabilitation planning efforts. Further research is proposed for a laboratory investigation with known internal deck condition to determine the influence from the cracking in the overlay level and damage in the deck on the UTD scan results.