On the Mechanical Modeling of Asphalt Matrix and Hot Mix Asphalt Mixtures

This paper discusses the mechanical modeling of the asphalt matrix (AM) and hot mix asphalt (HMA) mixtures for two types of aggregates and one asphalt grade. The AM gradation was extracted from the HMA gradation passing No. 8-sieve. Hydrated lime was used as a binder additive to investigate the improvement in mixture properties. A dynamic shear rheometer (DSR) was used to conduct frequency sweep and creep tests at various temperatures on AM specimens. An indirect tensile load test was conducted to determine the resilient modulus and the creep compliance of HMA mixtures. The master curves for complex shear moduli (G*) and creep compliance of AM were constructed using the data obtained at different temperatures from a DSR test. The G*-master curve data indicated improvements due to the hydrated lime addition for a range of frequencies, and were a function of aggregate type. The results showed that the generalized mechanical model (i.e., a combination of a Maxwel model and Kelvein models) can effectively characterize the creep response of both the AM and HMA mixtures. The study also focused on the application of a clustered distinct element two- dimensional (2-D) modeling (DEM) to predict the uniaxial compression modulus using a synthetic, heterogeneous microstructure reconstructed from scanned images of actual test specimens. The HMA 2-D microstructure was obtained by scanning HMA test specimens using a high-resolution scanner to obtain grayscale images. Bulk properties of the AM and aggregate structure were assigned and virtual compressive test simulations were conducted. The results indicated that the DEM simulation produced repeatable HMA moduli for a range of AM moduli, and can model the aggregate interactions, which represent some effects of the aggregate interlock in asphalt mixture. Furthermore, the micromechanical model using the DEM approach provides a reasonable physical portrayal of the force chains developed in the aggregate skeleton, which are known to be a critical aspect of HMA micromechanical modeling.