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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.

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

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.

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.

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.

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.

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.

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.

Moisture susceptibility is still one of the primary causes of distress in flexible pavements, reducing the pavements’ durability. A very large number of tests are available to evaluate the susceptibility of a binder aggregate combination. Tests can be conducted on the asphalt mixture, either in a loose or compacted form, or on the individual components of an asphalt pavement. Apart from various mechanisms and models, fundamental concepts have been proposed to calculate the thermodynamic tendency of a binder aggregate combination to adhere and/or debond under wet conditions. The aim of this review is to summarize literature findings and conclusions, regarding these concepts as carried out in the CEDR project FunDBits. The applied test methods, the obtained results, and the validation or predictability of these fundamental approaches are discussed.

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...

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...

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

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.

The morphology of bitumen-SBS blends is studied using Epi-Fluorescence microscopy. Morphology is defined as the partition of polymer-rich and bitumen-rich phases. Existing sample preparation methods for microscopy on bitumen are compared and the obtained morphologies are shown. In a second part, differences in morphology are related to differences in rheological behavior. The morphological properties strongly depend on the temperature, where a sample is taken, upon the cooling rate and upon isothermal annealing periods. During isothermal storage the morphology can undergo major changes. The so-called bulk morphology, which is obtained from a freeze-fractured surface, is different from the morphology seen on the surface which has been in contact with air or with silicon.

In this study, 26 bitumens covering a large variety in crude origin and processing conditions were evaluated, using rheological tests methods and the recently developed bitumen solubility model (BISOM) titrations. In BISOM, bitumen is characterised by its solubility in three different solvents, relating respectively to Van der Waals, polar and hydrogen bonding interactions. Since both BISOM and rheology produce a large number of data, and since it is not possible to change one parameter at a time, to investigate its influence, a statistical program SIMCA was used. In conclusion, it was found that stiffness versus temperature is, for unmodified bitumen, completely determined by the conventional test methods (penetration, R&B, viscosity) as was already stated by Heukelom. However, the shape of the phase angle with temperature or the elastic behaviour at a given stiffness shows a good relation with the parameters determining the hydrogen bonding potential and the polar interactions. The more hydroge...