Conventional Molecular Dynamics (MD) models of bitumen are built by homogeneously mixing molecules in a volume without considering that the molecules in bitumen are known to exhibit phase behavior and form distinctive molecular arrangements. These are known to have a significant impact in the behavior of bitumen, and considering their existence is paramount in producing improved representations of bitumen using computational models. This study explores whether MD models of bitumen that are conventionally assumed to be in equilibrium can still undergo significant phase separation over considerably long simulation times. It also aims to establish a more formal pathway to build and study models with highly heterogeneous arrangements of their molecules. Moreover, it aims to evaluate whether the presence of distinct morphologies have a significant impact in numerous physical properties of bitumen. The study shows that conventional and widely used models of bitumen exhibit significant molecular rearrangements over long times (>360 ns). It also shows that building heterogeneous morphologies is possible and result in energetically favorable conformations. Moreover, it proves that studying properties regularly used to validate MD models of bitumen (e.g., density) are insufficient in assessing the impact of different morphologies; more thorough methods are required to evaluate them.

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Bitumen is a key constitutive material in asphalt pavements. It binds together the rock scaffolding of a pavement. Bitumen provides asphalt pavement with flexibility and enables it to respond to traffic loading and return to its original condition after the loading, i.e. bitumen restores/repairs the damage. In Porous Asphalt (PA) or Stonemastic Asphalt Mix (SMA) asphalt mixtures, due its open graded structure, bitumen modifiers are used to improve or restore bitumen physical and mechanical performance. Traditionally bitumen modifiers are made with products of crude oil, such as: ethylene vinyl acetate (EVA) copolymers and styrene–butadiene–styrene (SBS). As crude oil production declines and the environmental and financial costs of crude oil extraction increase, there is a need to identify environmentally sustainable alternatives to use in bitumen. Bitumen modifiers generated from biological sources offer an environmentally friendly and economically viable alternative to crude oil based bitumen modifiers. This paper describes how PHBV (poly-3-hydroxybutyrate-co-3-hydroxyvalerate), a bio-based co-polymer, might be used as an alternative bitumen modifier. The effect of PHBV on 70/100pen was investigated for this paper. The chemical and physical effect of the PHBV on the bitumen performance was investigated using Gel Permeation Chromatography, Fourier Transformed Infrared Spectroscopy, Differential Scanning Calorimetry, microscopic imaging and Dynamic Shear Rheometer tests. The results indicate that PHBV has significant potential as a bitumen bio-polymer modifier.

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To further explore the long-term aging influence on the chemical properties of bitumen, laboratory aging methods were employed to obtain the aged binders with different long-term aging degrees. The chemical properties of virgin and various aged bitumen were evaluated through TCL-FID, ATR-FTIR, Elementary analysis and GPC tests. The chemical characterization results showed that as the aging degree deepened, the resin and asphaltene fractions with larger molecular weight increased dramatically, which resulted in the rise of average molecular weight and the more unevenly molecular weight distribution in aged bitumen. Moreover, the aging of bitumen would lead to the increase of the oxidized functional groups (C=O and S=O) index, oxygen content, aromaticity and polarity, while the reduction of carbon, hydrogen element contents and the H/C ratio.

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In the past years, the use of liquid additives as bitumen modifiers has increased to enhance or adjust the properties of bitumen for wide range of applications. Their molecular composition and mutual interaction result in a specific phase morphology in the binders. Hence, there is a need to evaluate the phase and interphase framework and physical properties of complex binders. The RILEM Technical Committee 272-PIM ‘Phase and Interphase behaviour of innovative bituminous Materials’, Task Group TG1 investigates the characterization of assessing phase interphase properties of complex bituminous binders. In this framework, three liquid additives have been selected with different viscosity, nature and use. They were blended with base bitumen to achieve similar consistency and the blends were further aged. Physical properties were evaluated through rheology using dynamic shear rheometer (DSR) in a wide range of conditions. The phase morphology was addressed by atomic force microscopy (AFM), differential scanning calorimetry (DSC) techniques. AFM and DSC results, from fresh and aged binders, reveal that each binder display specific phase morphology and glass transition characteristics, manifesting mutual compatibility of the individual binder components. This approach of binder assessment: combining phase characteristics and rheological response can assist material selection to specific applications.@en

The utilization of epoxy-based polymers as bituminous modifiers in developing durable and long-lasting pavement structures have gained increasing interest over the last years showing evidence of high performing materials (1-8). It has been noticed that the addition of epoxy-based modifier into bitumen lead to materials with superior characteristics against oxidative aging (1, 3, 8). Next to aging resistance, the incorporation of epoxy modifiers in bituminous materials has added functional benefits, such as improved resistance to moisture damage and fatigue cracking (5, 6). Despite the evidence of aging resistance in epoxy-asphalt concrete mixes, the influence of the epoxy-based polymers on the bitumen aging and the microstructure morphology of newly formed systems have not been fundamentally evaluated yet. Within the scope of this research, the aging susceptibility of epoxy modified bitumen has been investigated. The extent of aging has been probed by using a Fourier Transform Infrared spectrometer and also rheologically evaluated using a dynamic shear rheometer. Furthermore, an improved compatibility between epoxy and bitumen at the microstructural level defines the long-term chemo-mechanical performance of EB systems in a controlled manner. Thus, another aspect of this study was to investigate the morphological and interfacial characteristics of EB microstructure. @en