Feasibility of assessing bond condition of asphalt concrete layers with dynamic nondestructive testing

In the 1970s, the U.K. Transport Research Laboratory published a series of reports dealing with wearing course slippage due to debonding. At present, however, no accepted nondestructive test (NDT) technique exists for a reliable detection of poor bond. This paper outlines the research undertaken in developing an NDT method for quantifying bond condition beneath thin surfacings (10-50 mm). Laboratory experiments were conducted in the Pavement Test Facility at Nottingham University. A generic type of surfacing material was used and several interface conditions were compared: (1) bonded; (2) debonded; and (3) partially bonded. Different surfacing thicknesses were considered. An instrumented impulse hammer was used to provide the transient excitation, and vertical dynamic responses close to the point of impact were monitored using accelerometers. The results were used to identify suitable parameters for identification of bond condition. Cores taken at test points showed good agreement between the Leutner test results and the predicted condition of the interface. Finite-element (FE) analysis has also been performed to provide understanding of the response of thin surfacings with different degrees of bond. Results from the FE analysis confirm the trends established from the testing,