Field Validation of Falling Weight Deflectometer Deflection-Based Critical Strain Prediction Models for Full-Depth Asphalt Pavements

Critical strains are one of the most reliable mechanistic parameters representing the structural capacity of flexible pavements. However, critical strains are currently not considered in pavement management systems (PMS) because of a lack of methodology for measuring critical strains in in-service pavements. Recently, critical strain prediction models have been developed by the Indiana Department of Transportation and Purdue University research team to estimate the critical strains of existing full-depth asphalt pavements using falling weight deflectometer (FWD) data. Even though the accuracy of these models was verified with finite element (FE) analyses, additional field validation is needed before incorporating the model results into PMS. This study focuses on validation of these previously developed critical strain prediction models using field-measured strains. Nine field sections, representing typical full-depth asphalt pavements in Indiana, were selected for study inclusion. FWD testing was conducted on the field sections and field cores were collected. Field strains were measured by a strain gauge or were determined by FE analysis using the material properties obtained from the field cores. Based on the comparative analysis, the critical strain prediction models were successfully validated with strains measured from the field. The coefficients of determination were up to 0.98 for the transverse tensile strain at the bottom of the asphalt layer and 0.93 for the vertical compressive strain at the top of the subgrade. Therefore, it is concluded that the critical strain prediction models can be used to estimate critical strains of in-service full-depth asphalt pavements for structural evaluation of PMS.