THE USE OF COMPLEX MODULUS TO CHARACTERIZE THE PERFORMANCE OF ASPHALT MIXTURES AND PAVEMENTS IN FLORIDA

Abstract

The American Association of State Highway and Transportation Officials (AASHTO) 2002 flexible pavement design guide uses complex modulus as an input parameter for its performance models. A comprehensive project was undertaken to develop complex modulus capabilities in compression, torsion, and tension for Florida. Research was performed to evaluate how well the AASHTO 2002 proposed predictive dynamic modulus equation works for Florida mixtures. The results showed that the proposed predictive equation for dynamic modulus appears to work well for Florida mixtures. Potential relationships between the complex modulus and the rutting performance of mixtures were evaluated. No discernable relationship between complex modulus and rutting was established for mixtures of varying gradations and aggregate structure. Methods that can be used to obtain creep properties from complex modulus measurements as input into the Florida Hot Mix Asphalt Fracture Mechanics Model were evaluated. For the range of frequencies typically employed in dynamic modulus testing, it may not be possible to obtain creep compliance and creep compliance parameters accurately from dynamic measurements. However, an approach was developed for determining creep compliance parameters accurately from a combination of complex modulus and static creep tests. The effects of aggregate size distributions on the complex modulus were evaluated. A significant effect of gradation was found on dynamic modulus measurements. In conclusion, the complex modulus should generally neither be used to determine rutting or fracture resistance of mixtures. The primary use for the complex modulus test is to determine the stiffness of mixtures for purposes of determining the response to traffic loading, as per the new AASHTO 2002 flexible pavement design guide.