In-situ evaluation of microcrack damage and healing of asphalt concrete pavements using stress wave test

A nondestructive technique based on the stress wave propagation method is presented in this paper as a means of measuring the changes in the "apparent" modulus of an asphalt surface layer due to fatigue damage growth and healing during rest periods. This method was applied to four asphalt pavements in the FHWA Turner-Fairbank Highway Research Center that were loaded by the Accelerated Loading Facility (ALF) to induce fatigue damage. The results show that: (1) the test and analysis technique employed in this study provides a sensitive means of evaluating the changes in asphalt surface layer properties during fatigue loads and rest periods; (2) the elastic modulus of the asphalt layer decreases as the number of loading cycles increases in an S-shape decaying curve; and (3) the elastic modulus of the asphalt layer increases due to the introduction of rest between loading cycles.;The Artificial Neural Network (ANN) was used to predict the shear wave speeds of each layer from actual test data collected from pavements in Durham County (NC 54), Vass County (US 1), and Mn/Road Research Site. The multiple frequency analysis combined with ANN was successfully used for backcalculation of the layer moduli.