Crack distress causes asphalt pavement failure under repeated traffic loading. The objective of this study is to investigate the fracture properties of asphalt concrete through three dimensional (3D) numerical simulation using finite element method (FEM). The parameters and datum utilised for finite element models were captured from a grey matrix, which can be converted from digital images scanned by an X-ray computed tomography (CT) apparatus. Afterwards, the uniaxial compression test was simulated using FEM and was also conducted in laboratory to study the stress distribution and to evaluate the degree of damage during the loading process. Eighteen cylindrical asphalt concrete specimens were prepared with three different types of gradations: asphalt concrete, stone matrix asphalt and open-graded friction course. The uniaxial compression test was carried out on these specimens. Before and after each step, the specimens were scanned using X-ray CT to analyse the crack growth behaviour inside the asphalt concrete and to investigate the effect of gradation on the fracture characteristics. The degree of fracture can be evaluated by data analysis from the grey intensity histogram. The evaluation on asphalt concrete crack properties based on FEM with X-ray CT imaging was found to be practicable and reproducible. Additionally, the gradation was found to be an influential factor affecting the crack propagation of asphalt concrete.

In this paper, the role of crushing operation on the cubical controlling features of coarse aggregates, and its influence on the shape distribution characteristics of aggregates (i.e. angularity, sphericity, and flatness & elongation ratio) were investigated through the second version of Aggregate Image Measuring System (AIMS II). Three types of aggregate from different origins were chosen and crushed by the vertical shaft impactor (VSI) with fixed rotational speed. The results indicate that the rotation speed of VSI is influenced by the input power of the machine to the particle sizes, and higher speed leads to more cracks on aggregates during the crushing process. By using X-ray diffraction (XRD), the aggregate samples from different origins and mineral compositions were analysed under the same working operation of crusher. Besides that, the correlation between particle shape characteristics influenced by the mineralogical composition, and their collision behaviours have been discussed according to the tested results. A recommendation for optimal operation of VSI on crushing granite aggregates is given based on this study. Whereas, the cubical condition of aggregates and energy saving factors were taken into account. Furthermore, petrographic analyses were imposed to correlate particle mineralogy to its collision behaviour during crushing.

Variations in pavement density have been widely monitored and investigated, both in laboratory and in field experiments, since the compaction of pavement is so critical to its long-term performance quality. In contrast to field testing, laboratory tests are simpler to produce but less accurate. Destructive drilled samples are used to conduct field testing; however, they are limited in their ability to assess density information at specific areas. The use of computationally aided approaches, such as the Finite Element Method (FEM) and the Discrete Element Method (DEM), in research involving asphalt mixtures is increasing, since these methods simulate and evaluate the characteristics of asphalt mixtures at macroscopic and microscopic scales. Individual particle behavior at the microscopic level cannot be fully represented using the FEM alone, and the computing cost of utilizing the DEM approach alone is prohibitively high. The objective of this work is to simulate the pre-compaction process by using the coupled FEM-DEM approach. In order to investigate the impact of the asphalt mixtures’ gradation, a dense-graded asphalt mixture (AC 11) and a gap graded asphalt mixture (PA 11) were simulated. Different paving speeds (4, 5, and 6 m/min) were applied on the preliminary compaction model of AC 11 to study the effect of the paving speeds on the compaction process. By comparing the angular velocity, which worked as a reference of compaction quality, it was demonstrated that the grade AC 11 asphalt mixtures performed better in the preliminary compaction process compared to the grade PA 11 asphalt mixtures. Moreover, since it has an effect on compaction, paving speed was carefully monitored and kept within a reasonable range in order to maximize both pavement quality and project efficiency.