Comparison of Simple Performance Test |E * | of Accelerated Loading Facility Mixtures and Prediction |E * |

The dynamic modulus, |E^*|, of asphalt mixture has recently drawn much attention in the asphalt community. The |E^*| test has been suggested by NCHRP Projects 9-19 and 9-29 as the simple performance test (SPT) to verify the performance characteristics of Superpave® mixture design. In addition, it has been recommended as the potential quality control-quality assurance parameter in the field. The dynamic modulus, |E^*|, is an input to the Mechanistic-Empirical Pavement Design Guide (M-E PDG) and also supports the predictive performance models developed as part of NCHRP Project 1-37A. The importance of this parameter on one hand and its time-consuming determination on the other hand necessitated reliable prediction of dynamic moduli of asphalt mixtures at different temperatures and loading frequencies. In this respect, a number of predictive equations have been developed. The most widely used model is the NCHRP 1-37A, which is currently used for calculation of |E^*| in Levels 2 and 3 of M-E PDG. The model has a reasonably good prediction capability of high modulus values; however, it tends to over-predict the moduli at the lower spectrum. This study shows that a recent modification to the NCHRP 1-37A model has improved the overall prediction of |E^*| but has not significantly improved the overprediction of the lower moduli. While the replacement of the binder viscosity, η, with the binder shear modulus, |G^*|, has increased the accuracy of the model, the inclusion of the binder phase angle, δ, in the revised equation was not found to have a significant effect.