Laboratory assessment of nine methods for nondestructive evaluation of concrete bridge decks with overlays

Overlay systems have been extensively used to extend the service life of concrete bridge decks. There is, however, a lack of systematic studies on nondestructive evaluation (NDE) of concrete bridge decks with various overlays. This study assesses nine NDE methods for evaluation of concrete bridge decks with seven different types of overlays through laboratory concrete specimens. The nine NDE methods are sounding, ultrasonic surface waves (USW), impact echo (IE), ultrasonic testing (UT), impulse response (IR), ground-penetrating radar (GPR), electrical resistivity (ER), half-cell potential (HCP), and infrared thermography (IRT). The seven types of overlays are epoxy, latex modified concrete, silica fume modified concrete, polyester polymer, asphalt with a liquid membrane, asphalt with a sheet membrane, and asphalt without a membrane. Eight concrete specimens with various defects were built and nondestructively evaluated to acquire the detailed information of all embedded defects before placing overlays. One concrete specimen was kept bare as a reference, and the other seven specimens were covered with seven different overlays, respectively. Half of each overlay was bonded to the underlying concrete specimens, whereas the other half was debonded. NDE tests were carried out on the top of overlays. Based on the NDE test results, the applicability of each NDE method for concrete bridge decks with overlays is summarized as follows: (1) GPR and HCP are two effective methods for evaluation of the underlying concrete decks through both bonded and debonded overlays; (2) USW, IE, and UT can image the defects in the underlying concrete decks under bonded overlays, with the exception of the three asphalt overlays; (3) sounding, IR, and IRT can identify overlay debonding; and (4) ER is not effective due to electrical insulation of the overlay materials.