Under the repeated loading, the continuous impact and friction of tires on aggregates resulted in some changes in their morphology, which may cause rutting, decrease in skid resistance, and fatigue damage of the road. In order to explore specific changes in coarse aggregate morphology, the Los Angeles abrasion test was used to simulate the force exerted on coarse aggregates and the morphologies of different aggregates before and after abrasion were compared. Four types of coarse aggregates were selected and their mineral compositions were analyzed by X-Ray Diffraction (XRD). The morphological characteristics were measured using Aggregate Image Measurement System (AIMS-Ⅱ), including angularity, surface texture, sphericity and Flat and Elongation (F and E) ratio. Results showed that the angularity value for each type of aggregates significantly reduced after abrasion and the angularity reductions of various aggregates were consistent with the results of abrasion test, indicting the angularity reduction was the main component of abrasion loss. Whereas, there was no significant different between the surface texture of coarse aggregates before and after abrasion. For shape properties, both sphericity and F and E ratio results showed that aggregates with excessively high F and E ratio were easy to break, which might cause rutting and were harmful to pavement. Therefore, for pavements with high performance requirement, coarse aggregates with large angularity and low abrasion value should be preferred, whereas the quantity of particles with excessively high F and E ratio should be controlled.

The dynamic modulus ($|E^{*}|$ ) of asphalt mixtures is an important parameter in pavement design and analysis. Although the $|E^{*}|$ values of freshly prepared hot-mix asphalt (HMA) mixtures can be conveniently determined through laboratory tests, the $|E^{*}|$ values of field pavements continuously evolve as asphalt binder ages, and hence are difficult to determine. To examine the effects of asphalt binder aging on the $|E^{*}|$ of asphalt mixtures, a new piece of equipment is developed for the accelerated aging treatment of compacted asphalt mixture specimens. A set of small-size sampling, binder extraction, and recovery methods are used to determine the aging state of asphalt binder in asphalt mixtures. Three types of asphalt mixtures with different aging states are used to study the effects of aging on the $|E^{*}|$ changes. In addition, based on the $|E^{*}|$ test results, mixtures’ volumetric properties, and binders’ rheological properties at different aging states, the accuracy and robustness of six commonly used $|E^{*}|$ prediction models are compared. The developed equipment and method are anticipated to assist with the characterization of aged asphalt mixtures and the further improvement of $|E^{*}|$ prediction models.

High-temperature rheological properties of asphalt binders are important in asphalt mixture production and compaction. In this study, the high-temperature rheological properties of asphalt binders with polymeric, warm-mix, and rubber particulate additives were examined at different temperatures, shear rates, and shear modes. Most of the tests were conducted using a concentric cylinder measuring system with a dynamic shear rheometer. The test results provide a full picture of the rheological behaviors of those binders at or approaching the mixing and compaction temperatures. Test results indicate that shear rate dependency of modified asphalt binders at high temperatures is generally not significant and is related to binder type. The shear thinning behavior is more noticeable for binders with particulate modifiers than for those with styrene-butadiene-styrene (SBS) polymers. The apparent shear thinning behavior shown at high shear rates at relatively low temperatures may be attributed to discontinuity developed during the test. The test results also suggest that there are interactive effects between warm-mix additive type, binder type, and test conditions (temperature and shear rate). Hence, the effects of warm-mix additives may need to be considered at different combinations of temperatures and shear rates. The complex and rotational shear viscosities were found to be comparable at lower test frequencies (or shear rates), but not at higher ones, and the responses of different binders to shear modes were found to be different. Although this study does not aim to develop new criteria for mixing and compaction temperatures for asphalt mixtures with modified binders, the insights gained are expected to contribute to the body of knowledge in this area.

Fly ash is one of the industrial waste residues with significant emissions in China, and its rational utilization has important economic significance and environmental value. Due to the similarity in properties between fly ash and limestone mineral powder, it is possible to replace the mineral powder filler in asphalt concrete with fly ash. This article explored the feasibility of replacing the mineral powder with fly ash in an asphalt mixture through the study of fly-ash-modified asphalt mastic. Firstly, the microstructures and elemental compositions of fly ash and mineral powder were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Then, the rheological properties of asphalt mastics with different fillers were studied using dynamic shear rheological (DSR) tests. The results show that when the stress level was 3.2 kPa, the change in the J_nr value was different from that at 0.1 kPa, indicating that after increasing the stress level, the J_nr of fly ash asphalt mastic was smaller, and fly ash can improve the high-temperature creep performance of asphalt mastic. Replacing mineral powder with fly ash can improve the high-temperature rheological properties of asphalt mastic, but this damages the elastic and crack resistance properties of the asphalt mastic. In practical applications, partial substitution of mineral powder can be considered for the preparation of an asphalt mixture.