UC Davis Institute of Transportation Studies

Caltrans is in the process of implementing Mechanistic-Empirical design procedures. All mechanisticempirical methods must be validated/calibrated against the behavior of real pavements. This should be done before implementing models in design methods to ensure that designs will be reasonable. The Heavy Vehicle Simulator (HVS) provides a first step in this validation/calibration process. The short test section can be carefully constructed with well characterized materials and instrumented to measure the pavement response. The climatic conditions may be controlled or monitored closely and all load applications are known exactly. The pavement may also be tested until it fails. The HVS may be seen as “large scale” laboratory equipment, between the “small scale” laboratory equipment (triaxial tests, bending tests etc.) and the reality of real pavements, which have uncertainties regarding materials, loads and climatic conditions. The two HVSs owned by Caltrans have been used on 27 flexible pavement test sections, with varying combinations of asphalt and granular layers. Temperature control was used during the tests. Most sections have been instrumented with Multi-depth Deflectometers (MDDs) to compare the measured pavement deflections (at several depths) to the deflections predicted by mechanistic methods, during the full duration of tests carried to “failure” (in terms of rutting or cracking). Results from mechanistic models have been compared with the deflection measurements and performance as a first step prior to empirical calibrations with field results. The complete time history of each test has been compared rather than just the beginning and end measurements. This report presents the validation of the mechanistic models for asphalt fatigue and for permanent deformation with the HVS test results.