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The application of finite element modelling for assumed mesh elements is limited for asphalt mixtures because of the inclusion of air voids within the structure. A multiphase finite element (FE) model was applied to consider the effect of air voids on the properties of asphalt mixtures. The virtual microstructure of an asphalt mixture was incorporated into the FE model from the X-ray CT images of asphalt specimens. Considering the asphalt mixture as viscoelastic, the mechanical properties determined from laboratory tests were applied to the FE model. Analysis was performed on a representative volume element using the concept of continuum damage mechanics. It was found that X-ray CT images can be converted into a finite element mesh of the real geometry of the asphalt sample. It was also found from the analysis that the mesh generated from the actual geometry account of the stress concentrations due to air void distribution compared with the assumed simplified geometry. The FE model was also analysed using CAPA 3D to give a validation of the results.

This study investigated damage in asphalt due to moisture by using the modified saturation ageing tensile stiffness (SATS) test along with image analysis. Specimens made from both granite and limestone aggregate with a 40/60 penetration grade bitumen were tested in the modified SATS test. The samples were scanned within an X-ray CT facility before the SATS testing, after the initial saturation and at the completion of the SATS test. Bitumen was extracted from tested specimens and scanned separately in a high resolution Nanotom (high resolution X-ray CT). The extracted bitumen was tested in a DSR for shear rheological properties. The specimens made from granite (acidic) and limestone (basic) aggregate were found to have similar permeability and this was found to be high for specimens having high design air void content. Specimens made from basic aggregate had higher stiffness than the specimens made from acidic aggregate. The master curves of the aged binder are different from those of the virgin binder (bitumen). Also the microstructure of binder observed was different for aged and virgin binder.

Prediction of asphalt mixtures’ behavior during their service life is a challenge due to its complexity and sensitivity to environmental and loading conditions. It has been proved that, when subjected to loading conditions comparable with most pavement operating conditions, asphalt mixtures behave as linear visco-elastic (LVE) materials. Traditionally the LVE behavior of bituminous material is modeled via creep/recovery functions. In the past, several rheological models constituted by elastic and viscous elements arranged in series or in parallel (analogical models) have been proposed and specified for both bitumen and asphalt mixtures. The corresponding constitutive laws always involve first order derivatives of time with exponential type solutions but problems in setting parameters arise when both the creep and recovery behavior have to be modeled. In this paper it is shown that experimental creep data follow a power decay law, rather than an exponential one. As a consequence, a simple fractional model is here proposed for predicting creep/recovery behavior of asphalt mixtures with a small number of parameters and low computational efforts with respect to the classical analogical models. The proposed model is then calibrated by a best fitting procedure on experimental data from creep and creep/recovery tests carried out on asphalt mixtures under different load and temperature conditions.

This paper describes the development of a laboratory-based automatic torque bond test that is capable of quasi-static and repeated load interface testing. Results from quasi-static testing undertaken using either a controlled torque rate or a controlled rotation rate showed that the shear strengths and shear reaction moduli increased as the temperature decreased. Samples with interfaces treated with the cationic emulsion were found to display the highest shear strengths and those treated with no emulsion were found to display the lowest shear strengths. A reasonably good correlation was found between results from testing performed at 600 N m/min and testing performed at 180°/min. The nominal shear strength measured from a test performed at 180°/min was found to be approximately 1.9 times higher than the nominal shear strength measured from a test performed at 600 N m/min. The nominal shear reaction modulus from a test performed at 180°/min was found to be approximately 1.6 times higher than the nominal shear reaction modulus from the test performed at 600 N m/min. The effect of material compliance above and below the interface on the rotation of the interface and shear reaction modulus of the interface is likely to be relatively small unless the shear stiffness of these materials is very low and/or the thickness is large. Results from repeated load (fatigue) testing showed a higher fatigue life and greater sensitivity to shear stress level at the lower temperature.