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Re-refined Engine Oil Bottoms (REOB) has been used in recycled asphalt materials for flexible pavements in recent decade, due to its effects on softening aged binder and relatively low cost. However, concerns on the pavement performance of those materials including REOB in asphalt binders have been reported and linked to the use of REOB. Consequently, methods for detecting and quantifying REOB in asphalt binders have seen increased interest to control the use of these recycled oils. This study is for the first time to introduce the use of the Partial Least Squares (PLS) regression in Attenuated Total Reflection-Flourier Transformed Infrared (ATR-FTIR) spectroscopy analysis of asphalt binders for determining REOB content. The PLS regression analysis gives the advantage of using the whole ATR-FTIR spectroscopy of REOB blends. The results show that an accurate prediction model can be derived by using the PLS regression analysis on the ATR-FTIR spectra of REOB blends.

Rutting is one of the main asphalt pavement distresses, and it is believed that binder properties play an important role in mixture’s potential rutting resistance. Generally, in the Superpave design system asphalt binder is selected based on the binder PG grade required for the climate. However, to implement performance control through the traditional Superpave PG system during mix design faces more challenges due to the changes of oil refinery, asphalt binder modification, and the use of recycled materials in the mixture. This paper aims to investigate the role of asphalt binders and mix designs in the rutting resistance of asphalt mixtures. A total of 22 plant-produced mixtures from 10 states and 5 laboratory-produced mixtures were investigated for their rutting performance in this study. Those tested mixtures include various binder grades, aggregate sources, RAP contents, and mix designs. The Superpave binder rutting parameter G*/sinδ and Multiple Stress Creep and Recovery (MSCR) grade parameter Jnr3.2 are correlated with the mixture dynamic modulus and Hamburg Wheel Tracking (HWT) rutting parameters. In addition, the effects of other mix design variables on the rutting resistance are evaluated using a statistical analysis. The results show that by incorporating the binder properties and mix design variables, the stepwise regression fitting provides a much better prediction for HWT rutting parameters as compared to using only the binder properties. This indicates the importance of proper selection of the binder grade for mixture performance, and it also calls for justifying more focus on including mixture design variables to ensure acceptable mixture rutting performance. The statistical analysis can provide an insight into the use of artificial intelligence and machine learning by generating mathematical models for evaluating which mixture design variables are needed for better prediction of rutting performance.

Rutting resistance is one of the essential needs in the design of asphalt mixtures. Volumteric properties, binder modification, aggregates properties, and performance tests such as the triaxial test and wheel tracking test are used today to qualify the rutting resistance in practice. However, these tools are used on a trial and error basis and are mostly based on experience to achieve better resistance. With all the experience available today, it is still not clear what is the contribution of aggregate structure, what air-voids content should be used, and if plastomeric or elastomeric modifiers are preferred for better resistance. While compiling larger databases and expanding the types of aggregates and binders used in testing could help, a more fundamental understanding of how aggregate contacts are formed and how binders can contribute to actual mechanics of rutting resistance is a better path for designing of mixtures. In the last decade, a significant improvement in imaging and multi-scale modelling has been achieved, which allows looking closer at how binders and aggregates could affect rutting resistance. One of the most challenging aspects of this modelling effort is dealing with aggregates proximity zones or contacts and how the response of mixture changes when aggregates come into contact. This paper includes a proposal for addressing this challenge and provides a solution that is simple yet effective in better simulating of measured rutting in the laboratory. The paper also includes an application of the model to simulate mixtures produced with plastomeric and elastomeric modifiers with different viscoelastic properties. The mixtures include different gradations to represent fine and coarse gradations of aggregates. Results demonstrate that packing of the aggregates is significantly affected by the binder modifiers as some additives can result in a better-packed aggregate internal structure that is much more effective in improving rutting resistance of mixtures. It is expected that the improved modelling of contact zones will aid in more rational selection of aggregates and modification techniques in the mix design phase to enhance the rutting resistance of asphalt pavements.

To better understand oil modifiers’ effects on the performance of asphalt binders at low and intermediate temperatures and the mechanisms of the modification, laboratory tests including mechanical property tests and microscopy tests are performed. It is found that oil modifiers can improve the performance of asphalt binders at low and intermediate temperatures significantly. By comparing the absorption peaks of oil modifiers, neat binder and oil-modified asphalt, it is found that the oil modification of asphalt is mainly by physical modification. In addition, a new partition method using gel permeation chromatography spectrum is recommended to investigate the modification mechanism of oil-modified asphalts. With this new method, it is found that the large molecular size (LMS) content correlates well with low-temperature performance; parameter B calculated from fatigue equation correlates well with the content of medium molecular size (MMS), and fatigue life also has a relatively good relationship with LMS. Overall, it is shown that oil modifiers improve the performance of binders at low and intermediate temperatures by decreasing the LMS and MMS of contents.

Moisture damage of asphalt mixtures can be caused either by adhesive failure between asphalt binder and aggregate surface, or by cohesive failure within the asphalt mastic. There are limited studies on the effect of moisture on cohesive failure caused by asphalt mastic bonding deterioration measured by the Bitumen Bond Strength (BBS) test. The objective of this study is to determine the effects of different mineral fillers in asphalt mastic on moisture damage resistance using the BBS test. Results collected indicate that surface area and mineralogy of mineral fillers have significant effects on moisture damage resistance. Results also show that there is a significant effect of asphalt modification on moisture damage measurements. Thus, the concept of testing the mastic with the fillers and polymers intended for production of mixture appears to give an effective tool to predict the adhesion and cohesion performance before and after water conditioning.

Permanent deformation is known as one of the most critical distresses observed in asphalt pavements, and is known to depend on asphalt binder, aggregates and voids, which are the components of asphalt mixture. This study is an effort to investigate the effect of asphalt binder modification type and aggregate structure on rutting resistance through experimentation and finite-element simulation. Asphalt binders with different levels of non-recoverable compliance (Jnr) and elastic recovery (%R) based on the Multiple Stress Creep Recovery test were selected. Asphalt mixtures with different aggregate gradations were prepared for testing and image processing for numerical simulation. A flow number test was conducted on the mixture samples to obtain the asphalt mixture rutting performance. A two-dimensional (2D) image analysis was also conducted on the mixture samples to characterise their internal aggregate structures. In addition, a recently developed image-based multi-scale finite-element model was used to predict the permanent deformation of the asphalt mixtures. In this approach, four interconnected scales were modelled, namely asphalt binder, mastic, mortar and mixture scales through homogenisation and upscaling techniques to transfer the material properties from lower scale to higher scale. A novel approach for taking into account contact mechanics between aggregates as function of proximity is used at all scales. The simulation results show that by changing the aggregate gradation (packing), and the viscous component of asphalt binder (Jnr), the rutting resistance of asphalt mixtures can be significantly improved. However in comparison the elastic component of asphalt binder (% recovery) is not found to be a significant factor especially in a well-packed aggregate structure. The results raise questions about the focus by many agencies on the requirements of elastic recovery of binders as a tool to select modified binders for better high-temperature performance.