Local Practice of Assessing Dynamic Modulus Properties for Washington State Mixtures

The dynamic modulus (|E^*|) is one of the key elements of a mechanistic–empirical–based flexible pavement design procedure. The dynamic modulus is used to characterize the material properties of asphalt mixtures and to determine the stress–strain responses of a pavement at different loading conditions. The dynamic modulus is also a direct input parameter in several pavement performance models to estimate field fatigue cracking and rutting performance. To provide a better understanding of the local materials, this study aimed to test the typical asphalt mixtures used by the Washington State Department of Transportation and to establish a material catalog for dynamic modulus. In this study, seven plant-produced mixtures from five regions of Washington State were sampled and tested. These mixtures represented the typical asphalt binder, gradation, and mix designs of the state. One warm-mix asphalt project was also included in the analysis. On the basis of the experimental results, it was found that mix properties including air voids and binder properties had an important impact on the dynamic modulus. Because of the limited aggregate gradations, the effect of aggregate gradation on the dynamic modulus was inconclusive. The measured dynamic modulus data were compared with the prediction results by using the traditional Witczak E* model, the new Witczak E^* model, and the Hirsch model. The Hirsch model was found to be the most promising and was modified further by including mastic property into the model. The modified Hirsch model greatly improved prediction quality and can be used as both a design tool and a screening tool to estimate the dynamic modulus of a mixture at early stages of the mix design process.