Calibration of Witczak and Modified Witczak Models for Prediction of Dynamic Modulus of In-Service Asphalt Layers

One of the important input parameters of the Mechanistic-Empirical Pavement Design Guide (MEPDG) for asphalt pavements is the dynamic modulus (|E*|) that can be defined as the viscoelastic property of asphalt materials. For the determination of dynamic modulus of in-service asphalt layers, MEPDG uses results of both Falling Weight Deflectometer (FWD) and laboratory dynamic modulus predictive models. This method in some cases lacks precision. Hence, it is needed to improve the current method and develop accurate predictive models. In this research, ten asphalt pavement sites, having various structures, ages, and conditions, were selected in Khuzestan and Kerman provinces in Iran. Field and laboratory testing were performed and the dynamic modulus of in-service asphalt layers was determined. Developed predictive models for dynamic modulus of asphalt mixes including Witczak and Modified Witczak were calibrated and new models were constructed for predicting in-situ dynamic modulus of asphalt layers. These two calibrated models entitled “In-situ Witczak Model” and “In-situ Modified Witczak Model” could be directly used for the prediction of dynamic modulus of in-service asphalt layers from volumetric properties of asphalt mixes and viscosity characteristics of extracted binders without any need for FWD testing. Performance evaluation and validation of new models showed high accuracy and low bias with a very good correlation between predicted and measured values (R2=0.93).