Field Measurement of Vertical Strain in Asphalt Concrete

Recently developed Mechanistic-Empirical Pavement Design Guide (MEPDG) determines the probable total rutting by summing up the deformations of all layers of the trial pavement. If all distresses outcomes including rutting are within the specification the trial section is designed for construction. Therefore, vertical deformation (or strain) needs to be measured to validate the MEPDG for local conditions. However, no direct procedure for measuring the vertical strain in flexible pavement is available to this date. Traditionally, Earth Pressure Cell (EPC) is used to measure the vertical stresses at different layers of pavement. Then, vertical strain is calculated using the measured stress and the stiffness of the corresponding material. The present study describes a procedure to measure the vertical strain of asphalt concrete based on field instrumentation. The vertical strain is measured using the Vertical Asphalt Strain Gauge (VASG) in an instrumented pavement section on Interstate 40 (I40) in the state of New Mexico, USA and compares the results with numerical model developed using ABAQUS. The numerical model is validated with stress responses measured with installed four EPCs. The stiffness input of the numerical model is obtained from Falling Weight Deflectometer (FWD) test. Promising agreement is observed between the strains measured in the field and determined from the numerical model. Therefore, the VASG can be considered an effective sensor to measure the vertical strain of asphalt concrete in flexible pavement.