Modification of Dynamic Modulus Predictive Models for Asphalt ...

stiffness, and the “transition zone version” which is modified for the effects of film thickness.
The authors found out that a R-square value of 0.968 were observed for all three of the models.
Taking into account for the effects of mineral filler and film thickness did not improve the model
efficiency. In addition, a comparison between the Hirsch model and Witczak models were also
made. The comparison result is shown in Figure 11.
Figure 11: Predicted and Measured E* Values [10]
Figure 11 indicates the accuracies of Witczak and Hirsch models are on similar scales. At
low temperatures, the Hirsch model tends to be more effective.
University of Florida Study [31]
The study is focusing on the efficiency of Witczak model (1999) on predicting the dynamic
modulus of Florida mixtures. Twenty eight commonly used mixtures in the state of Florida were
studied. Three methods were used to obtain binder viscosities including: 1. directly test asphalt
viscosities with Brookfield viscometer; 2. calculate viscosities by shear modulus and phase angle
values from DSR test; 3. use empirical A and VTS parameters recommended by Witczak and
Fonseca for mix/laydown condition. The results are shown in Figure 12 through Figure 14
respectively.
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