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Field ageing is investigated based on recovered binders. Fifteen sections were considered, consisting of unmodified and polymer-modified binders (PmB). Binders were recovered from the wearing cours...

Field ageing gradients of bitumen samples recovered from 14 asphalt road sections were investigated via rheological and chemical characterizations and statistical analysis. The effects of air voids and environmental factors on the ageing gradient were evaluated using the field ageing and climate data. The effectiveness of the pressure ageing vessel (PAV) test was assessed in accelerating the bitumen’s long-term ageing by comparing with the field ageing data. Critical factors for field ageing were identified using statistical methods. A statistical model for the Glover-Rowe (G-R) parameter was formulated and verified by incorporating the screened key factors. Results indicate that a threshold air void content (around 6%) exists in differentiating the field ageing gradient patterns in the asphalt pavements. An increasing tendency is observed between the ageing gradient and annual days below 0°C. The chemical indices, stiffness-related indices, and G-R parameter can quantify the field ageing gradient of asphalt pavements. The PAV test can condition the bottom slices’ bitumen to the same ageing level as that in a pavement depth of 0.5–2 cm after 8 years’ field service. Pavement service life, binder content, minimum temperature, days above 32°C, and days below 0°C are the critical material and environmental factors that significantly affect bitumen’s complex shear modulus, crossover frequency, G-R parameter, and Δ Tc. The statistical model is verified with an acceptable mean absolute error of 28.1% and a R2 value of 0.95.

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.

Funding Information: The authors would like to acknowledge the contributions of the active members of the RILEM technical committee TC 264-RAP in terms of experimental results, data analysis and proofreading. The authors would also like to thank Nynas AB, Kraton Chemical BV and Technical University of Braunschweig for supporting the interlaboratory activity by providing bituminous materials, ARA and RA binder. Publisher Copyright: © 2022, The Author(s). This recommendation is based on the results of an inter-laboratory study organised by the RILEM technical committee TC 264-RAP "Asphalt Pavement Recycling"—Task Group 3 (TG3) focusing on Asphalt Binder for Recycled Asphalt Mixture. The TG3 aimed to evaluate the effect of a specific family of materials known as asphalt recycling agent (ARA) on the aged binder under different configurations. Even though ageing is an irreversible phenomenon, effective ARA must have the capability to improve the flexibility of the bituminous materials and their resistance against cracking susceptibility with no adverse effect on the rutting resistance of pavements containing reclaimed asphalt. A total of 17 participating laboratories analysed the properties of binder blends composed of aged binder from reclaimed asphalt in three different contents (60, 80, 100%), ARA and virgin binder. The physical properties of the blends were thoroughly evaluated through traditional and rheological binder testing. This recommendation proposes to restore the original material properties at low and intermediate temperatures (i.e. cracking resistance) while balancing the high-temperature characteristics (i.e. rutting susceptibility) with durable impact throughout the progression of ageing phenomena. Therefore, useing of the Dynamic Shear Rheometer is foreseen as a more suitable and sustainable means to evaluate binder blends containing an asphalt recycling agent. Compared with conventional testing, the proposed approach requires fewer materials while resulting in a faster experimental procedure with one single test.

Oxidative ageing in field asphalt pavements is a complex process with coupled multiple physics. This parametric study uses Multiphysics modelling approaches to evaluate the effects of material thermal properties, air voids content and distribution, mastic coating thickness, oxygen accessibility and binder oxidative kinetics on the spatial and temporal evolution of the oxidative ageing in the asphalt pavements. Results suggest that increasing the thermal conductivity of asphalt layers leads to a lower ageing gradient. The variations of base and subgrade layers’ thermal properties cause little to no effects on the oxidative ageing. A high activation energy of the asphalt binder (e.g. by adding anti-ageing additives) reduces the oxidative ageing significantly. Asphalt layers built on unbound granular base will experience greater overall ageing with a C-shaped ageing gradient compared to that built on treated base. Air voids content of

In literature, microscopy techniques including atomic force microscopy (AFM), scanning electron microscopy (SEM) and recently also confocal laser scanning microscopy (CLSM) have been used to study the microstructure of bitumen. Es-pecially by AFM, various surface morphologies have been observed. Well-known are the so-called Bee structures, related to a regular height profile of lower and higher regions. The appearance of these microstructures has been linked to the presence of crystallizing waxes. In addition to this, other regions surround-ing, or in between the Bee structures have been described. These have been re-ferred to as the perpetua or peri structures, and very little is known about the origin or formation of these phases. In this study, straight, saturated hydrocarbons of specific chain lengths, were added to a wax-free naphthenic bitumen, and the air-bitumen interfaces were in-vestigated by AFM. As expected, the unmodified bitumen did not display any topological microstructure, and by adding waxes to this binder, Bee structures could be generated. However, not only Bee structures were obvious, but the in-termediate phases could also be generated under certain conditions. The chain length of the waxes, as well as their blending ratios were the determining parame-ters for the type of structures that were formed. So, in conclusion, this study demonstrates that not only the Bee structures, but also the intermediate and/or surrounding structures are related to the presence of waxy hydrocarbons, and no other molecular structures are needed or involved in the formation of these structures.

Bitumen is a complex mixture whose composition–structure-property relationships are not well-understood. Therefore, it is essential to understand which components may develop microstructures, how and when these features appear, and if they are initiated or influenced by other components. Many studies have reported so- called bee structures as well as other phases on bitumen surfaces. A large number of observations point to-wards the crystallinity of waxy compounds as an explanation for the bees. However, doubt remains about the origin of the other phases and the possibility of other bitumen components as promoters of the bee formation. In this study, bee structures were investigated using two microscopy techniques: atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). By using model wax compounds, especially blends of waxes differing in melting points and chain lengths, bee structures and surrounding islands were created on featureless bitumen surfaces. Structures very similar to what is observed on a paraffinic bitumen were obtained. This in-dicates that bees and the surrounding areas both consist of crystallisable components. Moreover, bee structures were also generated on other surfaces, such as mineral oil and a maltene fraction. Bee formation is not limited to bituminous materials and bitumen components are not needed as promotors. Furthermore, CLSM offers possi-bilities to scan through transparent layers and to investigate surfaces under glass, for example. In contact with such a solid substrate, as well as after water submersion, no microstructural features were observed. Adding a combination of n-alkanes, to transparent oil, induced bee structures at the oil-air interface. The transparency of the oil allowed the visualization of wax crystallization in the bulk, where the added waxes crystallize as small particles. These small crystals are expected to influence the mechanical properties, such as low-temperature stiffening effects, which have been reported for paraffinic bitumen.

The use of rejuvenators has seen a consistent increase over the years in the asphalt pavement industry. This is due to the need for maximizing the demand for incorporating a higher amount of Reclaimed Asphalt (RA) in the pavement asphalt mixtures. In order to tackle this challenge, the Task Group 3, focusing on asphalt binders and additives, of the RILEM TC RAP conducted an interlaboratory activity to evaluate the effect of aging on blends of virgin and rejuvenated RA binders. A set of conventional tests including penetration value at 25 °C, softening point temperature and rheological measurements by means of Dynamic Shear Rheometer (DSR) were selected to involve a large number of participants. A binder, recovered from field RA, was treated with a bio-based rejuvenator and blended with a virgin binder to simulate recycling at three different percentages 60, 80, and 100%. These blends, as well as the pure virgin binder, were next short and long term aged and tested to evaluate the changes in the corresponding properties. Relatively consistent results were obtained for the entire set of blends. The aging of combined rejuvenated RA and virgin binders was comparable to that experienced for the pure virgin binder. DSR data provided a more precise evolution of the impact of aging on the materials.

Microstructures of bitumen surfaces (both air-cooled and fractured) were imaged by atomic force microscopy (AFM) and chemically characterised by time-of-flight secondary ion mass spectrometry (TOF-SIMS). For certain air-cooled bitumen surfaces, bee structures were observed by AFM, and chemical explanation by wax crystallisation was confirmed by TOF-SIMS analysis. Unlike the air-cooled surfaces, the fracture surfaces generally did not show clear structure patterns. Furthermore, TOF-SIMS analysis was conducted on the tube-like or worm structures which were generated by environmental scanning electron microscopy (ESEM) on the bitumen surfaces. In general, very small chemical differences were observed between the structured and unstructured areas, as well as between different areas of the structure. To understand the formation of the ESEM structures, possible contributing factors were examined, from which a mechanism involving electron-induced heating was proposed.

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.

Bitumen’s surface microstructure is in general well-documented and most recent theories postulate the effect of crystalline wax on the so-called bee structures. Although it is widely accepted that ageing has an effect on this unique microstructure yet conflicting literature exists on clear trends. This paper explores the effect of ageing on the bee structures of bitumen, employing two advanced microscopic techniques: an Atomic Force Microscopy (AFM) and a Confocal Laser Scanning Microscopy (CLSM). Four waxy and two wax-free bituminous binders are investigated before and after sequential laboratory short- and long-term ageing. The study demonstrates that the number of bees per μm2 and bee area percentage decrease with ageing, whereas their size is increasing. A systematic analysis of the waveform characteristics is also provided for the peaks and valleys as well as the shape probabilistic values of the bee structures. In conclusion, the results of the two techniques are in good agreement, reporting similar trends upon ageing for the relative bee density. Differences are mainly identified in the waveform calculations. It is believed that this systematic investigation may assist in enhancing the understanding of the effect of ageing on the surface microstructure, the wax distribution as well as on the wax crystallisation.

Understanding the fundamental mechanisms of oxidative ageing in bitumen is considered of paramount importance in order to take steps towards durable binders able to tackle distresses related to this phenomenon which deteriorates the asphalt performance. This paper focuses on the identification of the intermediate and final oxygenated products after short- and long-term laboratory ageing simulated with rolling thin-film oven testing (RTFOT) and pressurised ageing vessel (PAV) respectively. Three binders were investigated in this study, two originated from the same wax-free crude source, while the third was obtained from a different source, containing natural wax, and followed a different manufacturing process. Fourier-Transform Infrared (FTIR) spectroscopy demonstrated a clear increase of the sulfoxide and carbonyl functional groups upon ageing for all the binders independently of origin, manufacturing or performance. Electron Paramagnetic Resonance (EPR) spectroscopy showed an increase of the organic carbon-centred radicals after short-term ageing (RTFOT), whereas after PAV these radicals remained constant in the two wax-free binders originating from the same crude source, and even decreased for the third, waxy binder. Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy reported differences in the relative distribution of protons between the binders in the unaged state, and similar minor changes after both ageing steps regardless of the binder's crude source and distillation. The results of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) revealed that SOx- and (OH)x-containing compounds are produced after the sequentially occurring short- and long-term ageing in both wax-free bitumens, whereas an almost constant behaviour of aliphatics after PAV ageing can be seen for the same bitumens. Finally, the strengths and weaknesses of each of these experimental techniques were reviewed and compared versus the obtained results and possible ageing mechanisms.

Since cleaning of artworks is a nonreversible procedure, it is mandatory to adopt the proper cleaning technique which has the ability to remove undesired materials whilst preserving the original surface and, if present, the original ‘patina’ of the surface layer. In this regard, numerous gels have been developed and exploited for the cleaning of various artwork surfaces. Lately, agarose (AG) and polyvinyl alcohol-borax (PVA-B) hydrogels have been widely employed as cleaning tools by conservators-restorers. Both hydrogels show some limitations in specific cleaning practices. In this work, we investigated the influence of including increased levels of agarose into PVA-B systems. For this reason, we performed a detailed characterization on the double network (DN) hydrogel including the chemical structure, the liquid phase retention, the rheological behaviour, and the self-healing behaviour of various PVA-B/AG double network hydrogels. These new hydrogels revealed better properties than PVA-B hydrogels and obviated their limitations. The inclusion of AG into PVA-B systems enhanced the liquid retention capacity, shape-stability, and mechanical strength of the blend. Furthermore, AG minimized the expelling/syneresis issue that occurs when loading PVA-B systems with non-polar solvents or chelating agents. The resultant double network hydrogel exhibits relevant self-healing properties. The PVA-B/AG double network is a new and useful cleaning tool that can be added to the conservators-restorers’ tool-kit. It is ideal for cleaning procedures dealing with porous and complex structured surfaces, vertical surfaces and for long time applications.

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.

Asphaltenes and maltenes of bitumen before and after aging are investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), time of flight - secondary ion mass spectrometry (TOF-SIMS), and gel permeation chromatography (GPC). It has been shown that bitumen differs in terms of wax. After fractionation, more wax is found in the maltenes compared to the bitumen, and this is even more evident when bitumen is aged. For one bitumen, asphaltenes from the virgin binder do not contain carbonyls, which all fall into the maltenes. After bitumen aging, a large part of the carbonyl and sulfoxide signals is shifted to the asphaltenes. Differences in aromaticity are also evidenced as asphaltenes > bitumen > maltenes. TOF-SIMS shows that maltenes are close to the bitumen, but asphaltenes are more different. Also, maltenes are relatively unaffected by aging while larger differences are found in the asphaltenes between the virgin and aged binders. By GPC, a large molecular weight fraction of bitumen is shown as main part of the asphaltenes. However, asphaltenes also contain low molecular weight molecules that overlap with maltenes. Upon bitumen aging, some low molecular weight compounds may become part of asphaltenes, making the average molecular weight of the asphaltenes lower.

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.

Nowadays, Reclaimed Asphalt (RA) is widely used in pavement applications as part of new asphalt mixtures. To design high-quality asphalt mixes, the RA material and especially the RA binder must be systematically characterised with the purpose to explore its ageing state, especially when RA is added in high rates (above 20%). In this research, chemical (SARA and FTIR ageing indexes) and rheological properties (master curve parameters, Glower-Rowe parameter and ΔΤc) of a large selection of RA binders (19 samples) were determined to reveal their ageing level. The results of this experimental validation were further analysed statistically to discover clusters of similar chemorheological properties, reflecting in this way their ageing state. The exploratory techniques PCA and HCA were able to detect five clusters of RA binders with different ageing states. The five clusters clearly distinguish the RA binders in groups with statistically different properties, assessed using one-way ANOVA. The method proposed here is a potential tool to “fingerprint” RA binders with similar ageing states, particularly for decision-making strategies, to optimise the use and treatment of RA.

In this study, the feasibility of a natural peat fiber and finely ground peat powder as a modifier for bitumen was investigated. Initially, the as-received peat material was characterized in detail: the material was ground to various degrees, separated into fiber and powder fractions, and the gradation of the powder fraction as well as the size of the fibers were determined. A possible solubility in bitumen, the moisture content, and the density of both fractions were evaluated, and a limited chemical characterization of the fibers was conducted. Secondly, the rheological behavior of the powder and the fibers when blended with bitumen was evaluated. Additionally, a limited asphalt study was conducted. The rheological data showed the stiffening effects of the powder fraction and the presence of a fiber network, which were obvious as a plateau modulus towards lower frequencies. The fiber network was strain-dependent and showed elastic effects. This was further confirmed by the multiple stress creep recovery (MSCRT) tests. These tests also indicated that the fibers should improve the rutting resistance, although it was not possible to confirm this in asphalt rutting tests. Asphalt drainage tests demonstrated that adding dry peat, whether this is ground or not, is effective in reducing the binder drainage. However, the data also revealed that the amount of added peat fibers and powder should be limited to avoid difficulties in the compaction of these asphalt mixes.

Microstructures of bitumen were investigated using atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM), and a chemical characterization was successfully carried out using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The bee structures were observed by AFM, for which a chemical explanation by wax was confirmed by the TOF-SIMS analysis. A tube pattern or worm structures were generated and visualized by ESEM on bitumen surfaces. Chemical differences between the structured and unstructured areas, as well as between different areas of the structure, were observed. A mechanism for the structure formation on bitumen surface during ESEM analysis is suggested.

These recommendations are based on the results of a round robin test organised by the RILEM technical committee TC 237-SIB "Testing and characterization of sustainable innovative bituminous materials and systems". The Task Group 1 (TG1) focused on binder testing. The aim of the TG1 was to further understand the fundamental mechanism of water interaction in asphalt mixture, and to review the various test methods available to evaluate the affinity of bituminous binders to aggregate surfaces. A total of 13 laboratories participated, running different test methods. Three bituminous binders and four aggregate types were selected for testing. These recommendations focus on the main aspects related to testing procedure, measurement and presentation of results. While some qualitative trends are observed, there is still a wide scattering in results both within the same test method and between test methods. This is not only related to a visual interpretation of the degree of bitumen coverage, but also theoretical and numerical analyses of test results. The overall recommendation is to consider the results within qualitative classes.

In this study, the suitability of a natural peat fiber, as a modifier for bitumen was investigated. Peat fibers were dried, ground, and fractionated into a fiber and a granular fraction. Rheological data on peat modified binders indicated that the granular fraction is acting as a filler mainly stiffening the bituminous binders whilst the fiber fraction mainly increases the elastic behavior, which became especially visible at higher service temperatures. It was observed that by changing the ratio of fibers versus granular particles, the rheological behavior can be regulated. In addition, drainage tests were carried out on stone mastic asphalt (SMA) mixes. The data indicated that peat fibers can effectively reduce drainage, and can be used as an alternative for the currently used cellulose fibers.

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.

Polymer modification is widely used to improve the engineering properties of bitumen, the most commonly used polymer modifier being styrene-butadiene-styrene (SBS) block copolymer. Although extensive studies have been performed on polymer modified bitumen (PMB), no reliable data is currently available on the effect of polymer modification on the dynamic rheological properties at low temperatures. In this study, we focus on the rheology of SBS modified bitumen near and below the glass transition temperature (Tg) using the 4-mm DSR technique. In addition, fluorescence microscopy and temperature-modulated differential scanning calorimetry are used to study the phase behavior and interactions in the SBS-bitumen blends. At high SBS concentrations, thermorheological complexity is observed in the investigated temperature range, attributable to the formation of a continuous SBS-rich network structure. In the case of compatible SBS-bitumen blends, a linear correlation is established between the flexural creep stiffness measured by bending beam rheometry (BBR) and the complex shear modulus measured by 4-mm DSR. Deviations from this linear trend are shown to result from the macro-phase separation induced by the poor compatibility of SBS and bitumen.

While extensive research efforts have been devoted to understand the dynamics of chemically and structurally simple glass-forming liquids (SGFLs), the viscoelasticity of chemically and structurally complex glass-forming liquids (CGFLs) has received only little attention. This study explores the rheological properties of CGFLs in the vicinity of the glass transition. Bitumen is selected as the model material for CGFLs due to its extremely complex chemical composition and microstructure, fast physical aging and thermorheological simplicity, and abundant availability. A comprehensive rheological analysis reveals a significant broadening of the glass transition dynamics in bitumen as compared to SGFLs. In particular, the relaxation time spectrum of bitumen is characterized by a broad distribution of long relaxation modes. This observation leads to the development of a new constitutive equation, named the broadened power-law spectrum model. In this model, the wide distribution of long relaxation times is describedby a power-law with positive exponent and a stretched exponential cut-off, with parameter β serving as a measure of the broadness of the distribution. This characteristic shape of the bitumen spectrum is attributed to the heterogeneous freezing of different molecular components of bitumen, i.e., to the coexistence of liquid and glassy micro-phases. Furthermore, as this type of heterogeneous glass transition behavior can be considered as a general feature of complex glass-forming systems, the broadened power-law spectrum model is expected to be valid for all types of CGFLs. Examples of the applicability of this model in various complex glass-forming systems are given.

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.

The chemical composition and structures of bitumen surfaces are characterised using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The effect of wax is considered by comparing a wax-free bitumen with a bitumen that contains natural wax and a wax-free bitumen to which a small amount of wax has been added. The results demonstrate that TOF-SIMS is a powerful method for the chemical characterisation of surface structures and phase segregation phenomena in bitumen. It is evident that the structures formed on the bitumen surface are closely related to the wax content and that these structures, as well as the surface in general, are enriched in wax-related compounds (aliphatic hydrocarbons with a high degree of saturation). For the wax-free bitumen, the surface is characterised by a homogeneous distribution without chemical variations or phase structures and by a stronger signal intensity from aromatic compounds. When adding wax to the wax-free bitumen, extensive wax segregation occurs, but differently from the natural waxy bitumen, no bee structures are observed. Furthermore, fracture surfaces of all the wax-containing samples reveal circular structures, which are distinctly different from those observed on the original surfaces. The obtained chemical knowledge on bitumen surfaces and phase structures is of fundamental importance to understand performance differences of this type of materials.

The multiple stress creep-recovery (MSCR) test was recently introduced to evaluate bituminous binders at high service temperatures, in particular to evaluate the stress or loading resistance. This test allows classifying binders at the high-performance graded temperature, according to the traffic loading, starting from standard, to heavy, very heavy and extreme traffic loading. It is the intention that this test includes nonlinear binder properties. In this study, five laboratories have participated in a round robin test to evaluate the repeatability and reproducibility of the parameters derived from the MSCR test. Nine different binders were evaluated, including unmodified, slightly and highly modified binders. The MSCR tests were conducted at 50°C, and each laboratory performed testing five times under repeatability conditions. The test results were analysed according to ISO 5725 and observations and reasons for deviating test results are discussed in detail.

In the days of concern about high energy consumption and global warming, all sectors of our society are scrutinised for potential savings of energy. One potential area for energy saving in the road construction sector is to make asphalt without heating the aggregates which is the current practice when making hot mix asphalt. Bitumen emulsions have been used to make cold mix asphalt, but uncertainties about the quality of the constructions have limited a wider use. Twenty years ago, an extensive development took place to improve cold mix asphalt to make it more sustainable. In the current paper, the development of an improved technology for the manufacture of cold asphalts using emulsions is described. The technique was used to produce a number of test roads to demonstrate performance. Several of the roads have now been in service for more than 15 years. The roads have been evaluated by sampling and analysis. It is shown that the roads have sustained excellently throughout the years and an evaluation of bi...

The purpose of this study is to evaluate how different binders react with polyphosphoric acid (PPA), and to contribute to a better understanding of this interaction. A number of bituminous binders were characterized before and after adding PPA, using rheological and chemical test methods, including FT-IR, uv-vis spectroscopy, NMR and gel permeation chromatography. The interaction with PPA is quantified as the change in softening point after adding a specific percentage of PPA. Most bitumen show an increase in R&B. Also in rheology, the stiffness increases, while the phase angle decreases when adding PPA. These observations are well-known and have been reported frequently by other authors. However, for one of the binders, small amounts of PPA lead to a decrease in R&B and to an increase in penetration. Rheological tests on this binder confirmed that the complex modulus decreases after adding PPA. These effects could be attributed to a precipitation, induced by PPA. This is very clear when investigating a drop of the bitumen-PPA blend in an optical microscope, and is also confirmed by storage stability tests. In conclusion, the findings suggest that PPA interacts with conjugated aromatic compounds, and this can in some cases lead to a precipitation.

Pavement durability is often linked with water damage either through raveling or loss of integrity, especially considering asphalt materials. A large number of tests exist to address the water sensitivity and affinity between aggregates and asphalt binder. In Rilem TC 237 SIB, TG1 looked at the common test methods used to evaluate the adhesion or affinity of asphalt binder to aggregate surfaces. One of the main purposes was to run a Round Robin Test to evaluate the reproducibility and repeatability of these test methods and to give recommendations for improvement. Three asphalt binders were selected, two unmodified and a polymer modified binder and four aggregate types with different mineralogy. This paper presents the first results obtained for the rolling bottle test. The influence of aggregate type is higher than that of the asphalt binder. While there are some potential trends after 24 h comparing the different combinations of aggregate and binder, there is still a lot of variability in the absolute results. The underlining reasons are not yet clearly identified.

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...

The original version of this article unfortunately contained a mistake. In Eq. (9), the words ‘sin’ and ‘with’ should not be written in italics. Please find below the correct Eq. 9.

In the past years a wide discussion has been held among asphalt researchers regarding the existence and interpretation of observed microstructures on bitumen surfaces. To investigate this, the RILEM technical committee on nano bituminous materials 231-NBM has conducted a round robin study combining differential scanning calorimetry (DSC) and Atomic Force Microscopy (AFM). From this, methods for performing DSC and AFM tests on bitumen samples and determination of the influence of wax on the observed phases, taking into account thermal history, sample preparation and annealing procedure, are presented and critically discussed. DSC is used to measure various properties and phenomena that indicate physical changes such as glass transition temperature (T g) and phase transition such as melting and crystallization. In the case of existence of wax, either natural or synthetic, it can further indicate the melting point of wax, that could be used to determine wax content. The results from seven laboratories show that T g temperatures obtained from the heating scans are more repeatable and easier to obtain in comparison to the cooling scans. No significant difference was noted for T g’s obtained from the first and second heating scans. AFM is an imaging tool used to characterize the microstructures on a bituminous surface. Using AFM three phases in the materials with wax could be distinguished. The changes in the phases observed with AFM for increases in temperature were correlated with the DSC curve, and it could be established that the so called “Bee” structure disappeared around the melting peak in the DSC curve. Thus, this research has confirmed the relation between the microstructures on a bitumen surface and the wax content., Materials and Structures, 47 (7), ISSN:1359-5997, ISSN:0025-5432, ISSN:1871-6873

In this paper, experimental support is provided showing the importance of polyaromaticity on the elastic properties of bituminous binders. Especially the size of the polyaromatic structures seems to play a crucial role. The observations indicate that larger conjugated aromatic structures provide stronger interactions and relate to the elastic behaviour at longer loading times or up to higher temperatures, while smaller aromatic structures determine more the elastic behaviour at short loading times or at low temperatures. In addition to aromatic interactions, natural wax can, upon crystallization, also induce increased elastic effects, especially at low frequencies. A large variety of binders was investigated: bitumen from straight distillation, visbreaking, solvent deasphalting and oxidation were included in the sample set. Average levels of aromaticity were determined by Fourier transform infrared (FT-IR) spectroscopy and by refractive index measurements. Chromatography combined with UV-visible absorption spectroscopy was used as an indicator of the average size of the aromatic structures. Rheological properties were determined using a dynamic shear rheometer, in a temperature range from 0 up to 90 °C. Good relations were observed between the phase angle measurements, at specific test conditions of frequency and temperature, and UV-vis absorption levels at specific wavelengths.

The application of Differential Scanning Calorimetry (DSC) has been proven useful in characterizing bituminous binders, distillates and crude oils. In this paper, results of the round robin test, organized by the Rilem TC 231 Nanotechnology-based Bituminous Materials (NBM) TG1 group are reported. The purpose is to investigate the repeatability and reproducibility of standard DSC measurements when applied to bituminous binders. In the full test program of the Rilem NBM group, DSC measurements are further compared to observations made in atomic force microscopy (AFM), AFM measurements are reported in a separate paper. Seven laboratories have participated in this round robin test. Four bituminous binders were investigated, containing various amounts of natural or added wax. The test program consisted of a well-defined isothermal annealing procedure, followed by a first heating and cooling scan, and afterwards followed by a second heating scan. At this stage, the data, as they were reported by the different participants, were compared. For the glass transition (Tg), mid temperatures, can be defined with a reasonable reproducibility, which improves if natural wax is not present. Regarding melting and crystallization, the shape of the melting curve is highly dependent on the thermal history of the samples. Peak temperatures of melting and crystallization phenomena were reported with a good reproducibility, while the reproducibility of melting enthalpies (or surface area’s under the melting and crystallization signals) was not satisfactory. Different reasons for this and recommendations for improving the results are discussed in the paper.

Based on a catalogue of test roads in Denmark, four long lasting test sections constructed in the early 80's were selected for field sampling and extensive laboratory study. This paper focuses on characterizing the bituminous materials used in the test sections. First, asphalt cores were investigated in a non-destructive way using X-ray tomography and indirect tensile stiffness test. The field samples were further analyzed with respect to binder content, air void content, and aggregate gradation. To characterize recovered binders, both chemical and rheological tests were applied. It was found that the long lasting test sections consisted of thick asphalt layers of low air void contents. The wearing courses contained relatively high binder content except for one with a binder content of slightly below 6%. For all the test sections, no propagated cracks were observed. In achieving a long pavement lifetime, aging of bitumen was indicated as one of the key factors. Field aging of bitumen was strongly...

The potential benefits of producing and paving asphalt at lower temperatures are beyond discussion. There is already a lot of know-how on various techniques for producing warm mix asphalt, but there is insufficient data available about the impact of these techniques on the final performance characteristics of the asphalt. Nynas and BRRC are working together on a research project, to study the most important and promising warm mix techniques on laboratory; and field scale. These techniques are: the use of foamed bitumen, the addition of waxes to the bitumen and the addition of zeolites to the mixture. The present paper focuses on the last technique. The performance of warm asphalt mixtures produced with different types and quantities of zeolites is compared to the performance of a reference hot mix asphalt. Several aspects have been studied: compactability, permanent deformation, water sensitivity and low temperature cracking. Small scale field trials were made to validate the findings of the laboratory research.