Evaluation of the Impact Echo Method for Concrete Bridge Decks with Asphalt Overlays

Asphalt overlays have been commonly used to extend the service life of deteriorated concrete bridge decks. Nonlinear, viscoelastic asphalt has properties that differ considerably from the properties of the underlying portland cement concrete (PCC) deck. The impact echo (IE) method has been extensively used to nondestructively evaluate PCC structures. The method, however, performs differently on asphalt overlays, especially when a membrane is placed between the overlay and the deck. The general recommendation has been to perform IE tests on asphalt overlays in cold weather. The temperature range under which IE can be used, however, is still uncertain. This study was conducted to systematically examine IE performance on asphalt overlays. Three PCC specimens with three types of asphalt overlays―asphalt with a liquid membrane, asphalt with a sheet membrane, and asphalt without a membrane―were tested in a temperature chamber. The three PCC specimens had identical designs, materials, and artificial defects. The nondestructive evaluation (NDE) results from the tests indicate that: (1) 32°F and below is the appropriate temperature range for IE to detect defects in the underlying deck; and (2) membranes can significantly reduce the propagation of waves into the underlying deck.