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Bitumen characterisation and differentiation usually involve a combination of mechanical and chemical analyses. However, these methods provide limited information on the diversity caused by the binders' origin or processing method. Thus, the question arises whether the bitumen microstructure can be used to identify these issues. In this study, microscopic methods, including brightfield, darkfield and fluorescence optical inverse microscopy (OIM), as well as confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM), were used to investigate the bitumen surface. Five different binders varying in their origin and production method were selected. The results show that CLSM, AFM and OIM darkfield can adequately capture a specific surface microstructure known as the bee structure, whereas brightfield in the OIM and optical CLSM show the surrounding peri phase, which exhibits a strong fluorescence. All visbroken binders show bee structures surrounded by a pronounced peri phase. On the other hand, one of the straight distilled binders does not show any microstructure, while the second straight distilled binder displays smaller bee structures surrounded by a small peri phase. Results from the image processing evaluation reveal that the area covered by bee structures is in the range of 2.4 - 4.3% for those binders that developed a surface microstructure. These results indicate a good accordance between the three microscopic techniques selected. However, a clear differentiation between the binders is difficult to obtain. Nonetheless, this work shows how these techniques can be used to their maximum capabilities regarding the obtained microstructural information and may help solve future questions regarding ageing, modification or rejuvenation.

Rheological characterisation methods are important when it comes to a performance-based selection system for bituminous binders for road applications. Standardised methods exist for the determination of bitumen rheological behaviour based on a dynamic shear rheometer (DSR) at intermediate and high service temperatures and a bending beam rheometer (BBR) at low temperatures. Recently, a dynamic shear rheometer with 4 mm parallel plates (4-mm DSR), has been proposed by Western Research Institute (WRI), as a promising method to determine the rheological behaviour at low temperatures. Clear advantages of the 4-mm DSR are related to the small sample size, especially important for recovered and aged binders, and the ability to work with adequate stresses at very low temperatures. Furthermore, if 4-mm DSR can be used to assess the low temperature behaviour of bitumen, then the performance of a binder in the whole range of service temperatures, could be assessed by just one equipment, a DSR. This paper focuses on the challenges related to 4-mm DSR tests regarding equipment preparation, with a specific attention to the temperature assessment and calibration. Furthermore, a sample preparation method, assuring good adhesion to both plates is proposed and the repeatability and reproducibility of 4-mm DSR tests is evaluated.

The aim of this study is to characterize structures induced on bitumen surfaces under analysis by environmental scanning electron microscopy (ESEM), and to examine possible contributing factors to the formation of their formation. Various bitumen samples are investigated, including soft and hard, as well as polymer modified bitumen. Chemical characterization is carried out by time-of-flight secondary ion mass spectrometry (TOF-SIMS), combined with principle component analysis (PCA). The study shows that, for soft bitumen, a tube pattern or worm structure is rapidly formed during ESEM analysis, but for hard bitumen, a longer exposure time is needed to develop a structure. The structures on the hard bitumen are also denser as compared to those on the soft bitumen. When sample specimens are deformed or stretched, the orientation of the created deformation is clearly reflected in the structures formed under ESEM, and for soft bitumen, the structure disappears overnight in vacuum but reappears with the same pattern upon repeated ESEM analysis. TOF-SIMS shows small but consistent chemical differences, indicating higher aliphatic and lower aromatic contents on the surface of the structured area compared to the unstructured area. Based on an estimated temperature increase on the bitumen surface due to the electron-beam irradiation, it is speculated that the ESEM-induced worm structure may be attributed to evaporation of volatiles, surface hardening and local expansion. In addition, under the electron-beam exposure, certain chemical reactions (e.g. breaking of chemical bonds, chain scission and crosslinking) may take place, possibly resulting in the observed chemical differences between the structured and unstructured areas.

Bitumen, the heavy residue of crude oil, can display a rich microscale morphology, including so-called Bee structures. The use of Atomic Force Microscopy (AFM) measurements in literature strongly indicates that the appearance of Bee structures is related to the presence of paraffin wax crystals. Most studies have investigated standard bitumen surfaces when cooling bitumen in an air atmosphere. Only a few investigations have analysed surfaces formed in other media or have analysed fractured surfaces which relate to the bulk morphology. Although considerable research has focussed on identifying Bee structures, less attention has been paid to the Bee structure morphology of different bitumen types and the relations to other binder parameters. The comparison between the micro morphology of the air-oil interface compared to the bulk phase volume has been studied even less. In this experimental study, five bitumen samples were selected based on differences in their natural wax content. Both the air-cooled surface interface and fractured surfaces were characterised using AFM in tapping mode. All the air-cooled surfaces revealed Bee structures, except the wax-free bitumen, which did not display the presence of any Bee structure. None of the fracture surfaces revealed Bee structures. Reheating a fractured surface of a wax-containing bitumen transformed the morphology into Bee structures. The experiments demonstrate that Bee structures are present in different binders but display very different shapes and sizes. Flowever: image analysis indicates that the unit cell inside these structures is rather constant and independent of the binder type. This work confirms a relationship between natural wax and Bee structures and it also shows that Bee structures, as such, are a surface phenomenon which is not present in the bulk phase volume of samples. (C) 2018 Elsevier Ltd. All rights reserved.

In this experimental study, we explore the broadening of the glass transition in chemically and structurally complex glass-forming liquids (CGFLs) by means of thermal and rheological characterization techniques. Petroleum fluids with different levels of chemical and structural complexity are used as model materials. Thermal characterization by temperature-modulated differential scanning calorimetry (TMDSC) reveals a systematic increase in the width of the glass transition region ΔT g with increasing chemical and structural complexity. The broadening of the glass transition is also strongly reflected in the linear viscoelastic properties that are measured by small-diameter parallel plate rheometry. Most notably, this is observed as the broadening of the relaxation time spectrum at long times. The recently proposed broadened power-law spectrum model is used to describe the constitutive behavior of the investigated petroleum fluids. In this model, the stretching parameter β serves as a quantitative measure of the spectral broadening. A strong power-law correlation is found between ΔT g and β, manifesting a relationship between the broadness of the calorimetric and viscoelastic glass transition in CGFLs.

Oxidative ageing in bituminous materials is considered one of the most important factors for distress types in road applications. This paper aims to offer insights into the validity of commonly held beliefs regarding the oxidation phases of ageing in bitumen, the fast- and the slow-rate phase, and explore the main oxidation products formed upon ageing. In order to evaluate possible differences between bitumen types, the penetration grade as well as the bitumen production process was varied. Thus, the ageing of three different binders was first studied by Fourier-Transform Infrared (FTIR) and Electron Paramagnetic Resonance (EPR) spectroscopy. The formation of oxygen-containing molecular structures on the bitumen surface during ageing was studied with Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The results of FTIR reveal a gradual increase of sulfoxides upon ageing, while the EPR results show an increase of organic carbon-centred radicals. In parallel, TOF-SIMS results provide evidence for an increase of oxygenated compounds, such as SOx--, HOx-- and NOx--containing compounds. It appears also that paramagnetic metal species, such as vanadyl-porphyrins, are insusceptible during ageing. Overall, the findings of this study are in agreement with a mechanism comprising two rate-determining phases and support the formation of different oxygenated products. It is believed that the experimental approach used in this work may contribute further to an improved understanding of the ageing mechanisms in bitumen.

Rheological properties such as stiffness, elasticity, and viscosity are crucial parameters for the use of bitumen as a construction material. In bitumen oxidation studies, the increased viscosity has often been related to an increase in polar interactions from oxygen-containing compounds, like carbonyl groups. In this study, bitumen was subjected to two oxidation processes, aging and air blowing. Aging was performed using the rolling thin film oven test (RTFOT) and the pressure aging vessel (PAV), whereas air blowing was conducted in a laboratory unit. This investigation gives more insights in the changes observed during oxidation and highlights the differences between aging and air blowing. Moreover, the oxidation tests provide bitumen samples of increasing viscosity, which are used to evaluate relations between molecular and viscoelastic characteristics. As a comparison, the changes observed in harder bitumen samples prepared by a continued distillation are also included. As expected, the evolution of rheological properties with oxidation time is very similar in the PAV and in the air-blowing unit, although the timescales are very different. Fourier transform infrared spectroscopy (FT-IR) and acidity measurements reveal clear differences in the formation of oxygen-containing functional groups depending on the oxidation process. UV-visible spectroscopy shows that during aging as well as during air blowing, larger conjugated aromatic compounds are formed. These findings suggest that the formation of polyaromatic compounds may be the main contributor to the increase in elasticity and viscosity during oxidation.

The relation between the chemical composition of bitumen and the physical properties, such as viscosity or viscoelasticity is very important for the use of bitumen as an advanced construction material. In view of the limited understanding of the exact molecular structure of the millions of different molecules constituting bitumen, many different proposals for the structure of bitumen have been published over the last 100 years. In this paper we propose that interactions between the molecules are the main determinants for the physical properties of bitumen. We discuss different types of interactions, typical for hydrocarbons, such as dispersive London interactions, polar interactions and pi–pi interactions, and how the strength of the interactions may be estimated by different methods. We also discuss one class of molecules in bitumen, defined by non-solubility, the asphaltenes, and why they contribute strongly to the thickening effect of bitumen, but we also conclude that asphaltenes are not the only molecules contributing to viscosity. Finally we show how the use of molecular parameters like molecular weight and aromaticity can be used to give a good estimate of the viscosity of heavy hydrocarbons of different composition.

Binder properties, believed to relate to asphalt rutting, were investigated and compared with each other. Included are: parameters derived from oscillatory tests (e.g. the "zero" shear viscosity and the SHRP rutting parameter), parameters derived from static and repeated creep tests and the traditional R&B softening point. Various binders were tested, including low and high polymer modified bitumen, and bitumen modified with commercial waxes. This study shows that for unmodified bitumen all the investigated binder parameters correlate well with each other and would give similar classifications regarding the rutting susceptibility. For modified binders, the parameters related to low frequency or long loading times, give a different ranking than those related to higher frequencies, as for example the SHRP parameter. The storing and preparation conditions prior to the rheological measurement can have a large influence, especially in the range of long loading times or low frequencies. For elastomer modified binders, the homogenization temperature and the corresponding change in micro-structure can have a large impact. For binders with semicrystalline modifiers, the storage time and storage temperature before testing can introduce large changes in the polymer network building up. The thermal history effects in rheological tests can be related to variations in crystallinity, as shown by calorimetry, or to variations in morphology, as revealed by fluorescence microscopy. Some of the binders were also investigated in the presence of filler, to see if the thermal effects play a similar role in mastic (binder(+)filler) as in the neat binder.

Test procedures, aiming at measuring fatigue directly on bituminous binders, are increasingly used. The purpose of this paper is to investigate the relevance of this type of binder fatigue tests and to compare the results with laboratory fatigue properties of the corresponding mixes, using one mix composition for all binders, and similar fatigue tests conditions. Eight binders were selected, derived from two crude sources, including an oxidised and two polymer modified samples. All fatigue tests were performed at equi-stiffness levels. A very good relation was seen for the e6 value (strain level at which fatigue occurs after one million cycles) in binder and corresponding mix fatigue tests, at least for the non polymer modified binders. The polymer modified samples showed an improved fatigue resistance in binder tests, which was only partially reflected in the asphalt mix tests. In addition, more structured binders, as for example after oxidation, showed better fatigue resistance especially at lo...