Aging during construction and in-service substantially changes the chemical composition and physical properties of bitumen thereof influences the performance of asphalt pavements. The modification of bitumen by crumb rubber modifier (CRM) significantly increases the complexity of the aging mechanism and is expected to improve the aging resistance of bitumen. This study aims to investigate the effects of laboratory short-term and long-term aging on the chemistry and rheology of crumb rubber modified bitumen (CRMB). Neat bitumen and CRMB with four different CRM contents were studied. Fourier transform infrared spectroscopy and dynamic shear rheometer were employed to measure the change in the chemical composition and rheological properties of binders at different aging states. Bitumen hardening, which was rheologically revealed by the frequency sweep and multiple creep recovery test results, was also reflected in the growth of carbonyl and sulfoxide functional groups. In addition, the aliphaticity and aromaticity indices of binders before and after aging were also investigated. CRMB binders showed improved aging resistance compared to neat bitumen as reflected by the decreased carbonyl and sulfoxide indices as well as the lower change in rheological parameters. Higher resistance against aging was achieved when increasing the CRM content. The results also highlight the correlation between chemistry and rheology of bitumen. Among six selected mechanical parameters of binder, the non-recoverable creep compliance and percent recovery show better correlations with the combined chemical aging index (sum of carbonyl and sulfoxide indices) than the parameters derived from the linear viscoelastic region.

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In-depth understanding of the synergetic effect between the various incorporating constituents in asphalt binders (e.g., polymers, fillers) is needed to design durable paving materials with desired properties. In this research, the focus was first on the effect of the reactivity of fillers on the evolution of adhesive strength between stone aggregates and epoxy modified asphalt mastics during the epoxy polymerization. Uniaxial tensile tests were performed on different combinations of fillers and binders with and without the epoxy-based polymer, and at different modification levels. Based on the results of the tensile tests, the increase of the adhesive strength of mastic with aggregates was generally lower when reactive filler particles (i.e., hydrated lime) were added than of epoxy binders with non-reactive filler. In other words, the non-reactive fillers did not influence the adhesion process and were thus selected for the next step studies on aging. The chemo-mechanical changes of epoxy modified asphalt mastics were analysed after pressure aging vessel and oven-conditioning after various aging times by means of Fourier transform infrared spectroscopy and dynamic shear rheometer. Less sulfoxides formed and higher modulus levels were measured with increasing the epoxy polymer in mastics over oven- and PAV-aging conditions. Due to the pressure difference, the rate of modulus increases and phase angle decrease was higher when the materials were conditioned in PAV than in oven.

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Recently warm mix asphalt (WMA) technologies have been introduced to rubberized asphalt mixtures to decrease the required construction temperatures and to alleviate the hazardous gas emissions. Rubberized asphalt pavements combining with WMA have the potential to improve the long-term pavement performance. This study aims to investigate the fatigue performance of crumb rubber modified bitumen (CRMB) containing warm-mix additives using different characterization methods. The effects of crumb rubber modifier (CRM) content (5%, 10%, 15% and 22% by weight of base bitumen) and warm-mix additives on the binder fatigue performance were investigated. Various laboratory tests, including frequency sweep tests, time sweep (TS) tests and linear amplitude sweep (LAS) tests, were conducted on the long-term aged binders to obtain indicators of fatigue performance. Results show that there is a good correlation between the measured fatigue life determined by TS tests using the dissipated energy concept and the predicted fatigue life determined by LAS tests using the simplified viscoelastic continuum damage (S-VECD) theory. However, the traditional Superpave fatigue parameter and the G-R parameter cannot characterize accurate enough the fatigue performance of modified binders. CRMB binders exhibit superior fatigue performance compared to the neat bitumen. The effects of warm-mix additives on the fatigue performance are different for neat bitumen compared to CRMB binder. Based on the findings in this study, rubberized asphalt mixture combining with WMA additives is expected to have a promising long-term fatigue performance.

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The addition of epoxy modifier in bitumen is a relatively new modification technology (1-4) and the most critical epoxy polymerization-induced changes of the epoxy-bituminous materials are not fully understood. Different phenomena take place when epoxy modifiers are incorporated into bitumen and they are dependent on the material hardening conditions. Temperature is one of the most crucial parameters that influences to the development of physical, chemical and mechanical characteristics at the early life (curing or chemical hardening - CH) (5-7) and long-term service (oxidative hardening - OH) (4) of epoxy-modified binders. For this reason, in-depth exploration of epoxy chemistry in bitumen is needed to understand the evolution of the properties of these binders in time. Within this framework, the chemical compounds and their reaction products generated under various conditions were studied to reveal the time dependency of molecular microstructures of modified binders. Special attention was given to the evaluation of physiochemical characteristics and the mechanical properties of epoxy-bituminous binders, concluding that the degree of CH and OH was dependent on the level of epoxy modification in bitumen. It was observed that the sulfoxide compounds are the most representative index for assessing the age hardening of epoxy-modified bitumens. Finally, the enhanced resistance against environmental aging in combination with the superior mechanical characteristics (i.e., higher tensile strength, flexibility and enhanced longevity) when the epoxy modification is implemented in bitumen promises a very effective technology for developing long-lasting pavement materials. @en

Induction heating driven polymerisation is an in-situ curing technique for epoxy-asphalt systems that maintains most of the advantages of temperature-driven polymerisation and it solves the need for longer curing time periods at lower temperatures before traffic can be allowed. In particular, induction heating can be utilised to accelerate the polymerisation of paving mixes with a thermo-hardening nature. In this study, steel fibres are dispersed in a mix and during exposure to an alternating electro-magnetic field generated by induction coils, they are heated leading to the rapid initiation of epoxy-asphalt polymerisation. This research presents the implementation of a finite element model analysis for assessing the potential of utilising steel fibres for the development of inductive mixes with sufficient induction heating efficiency. A produced and compacted mix with steel fibres was reconstructed by means of CT scans on samples from the mix and its effective electrical conductivity was calculated. Also, the electro-magnetic induction-driven polymerisation of epoxy-asphalt is simulated by extending a model developed elsewhere. The extended method can be used to predict the evolution of the curing process, and further of mechanical properties thereby indicating that electro-magnetic induction represents a reliable polymerisation method to cure epoxy-asphalt systems.@en

Many research on mechanistic testing have come to likely conclusion that different test setup results in different performance. The aim of this paper is to analyse the stiffness modulus resulting from three different test setups, namely; Monotonic Uniaxial Tension Test (MUTT), Monotonic Uniaxial Compression Test (MUCT), and Indirect Tensile Test (ITT). They are monotonic tests. This paper will elaborate if there is any significant difference among the result of the first three tests. Master curves of stiffness modulus as a function of strain rate at reference temperature of 15 C were developed. The results show that there is no significance difference between the modulus resulting from the three tests performed at high strain rates. It's also shown that at low strain rate, the elastic modulus resulting from compression tests is in between indirect and uniaxial tension test's elastic modulus.

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Epoxy modification of asphalt binders has been recognized as a very effective technology to alter the chemistry of asphaltic materials in such a way that long-lasting pavement structures can be designed. However, the phenomena that are involved to build up the physico-mechanical properties of epoxy asphalt systems are still unknown. The focus of this paper is on understanding the link between chemistry and the mechanical properties of epoxy asphalt binders during the thermo-irreversible process of chemical hardening. For this purpose, a constitutive model for predicting the evolution of cure-induced stresses in epoxy asphalt binders is proposed, and an experimental program was developed to determine the model parameters. The cure dependency of physico-mechanical parameters of modified binder was obtained and imported into the model to simulate the build-up of material properties during (non-)isothermal hardening of epoxy asphalt binder. The model is implemented in a commercially finite element tool by coupling the chemical, thermal, and mechanical phenomena with multi-physics strategies, and the results are analyzed to identify the influence of different heating conditions on the crosslinking density and subsequently on stress build-up. It was found that the amount of stress build-up during curing was strongly dependent on the heating conditions, and a higher rate of stress build-up was observed at higher applied temperatures. In other words, the processing conditions during in-plant material production or in-field manufacturing of structures made by epoxy asphalt systems affect the material hardening and subsequently the desired functionalities of pavement structures.@en

The addition of epoxy modifier in bitumen is a relatively new modification technology (1-4) and the most critical epoxy polymerization-induced changes of the epoxy-bituminous materials are not fully understood. Different phenomena take place when epoxy modifiers are incorporated into bitumen and they are dependent on the material hardening conditions. Temperature is one of the most crucial parameters that influences to the development of physical, chemical and mechanical characteristics at the early life (curing or chemical hardening - CH) (5-7) and long-term service (oxidative hardening - OH) (4) of epoxy-modified binders. For this reason, in-depth exploration of epoxy chemistry in bitumen is needed to understand the evolution of the properties of these binders in time. Within this framework, the chemical compounds and their reaction products generated under various conditions were studied to reveal the time dependency of molecular microstructures of modified binders. Special attention was given to the evaluation of physiochemical characteristics and the mechanical properties of epoxy-bituminous binders, concluding that the degree of CH and OH was dependent on the level of epoxy modification in bitumen. It was observed that the sulfoxide compounds are the most representative index for assessing the age hardening of epoxy-modified bitumens. Finally, the enhanced resistance against environmental aging in combination with the superior mechanical characteristics (i.e., higher tensile strength, flexibility and enhanced longevity) when the epoxy modification is implemented in bitumen promises a very effective technology for developing long-lasting pavement materials. @en

As bitumen oxidizes, material stiffening and embrittlement occur, and bitumen eventually cracks. The use of anti-oxidants, such as lignin, could be used to delay oxidative aging and to extend the lifetime of asphalt pavements. In this study, the chemical and rheological effect of lignin on bitumen was evaluated by using a single dosage organsolv lignin (10 wt.% dosage). A pressure aging vessel (PAV) was used to simulate the long-term aging process after performing the standard short-term aging procedure, and the lignin-modified bituminous binders were characterized by an environmental scanning electron microscope (ESEM), Fourier-transform infrared (FTIR) spectroscopy, and a dynamic shear rheometer (DSR). From the ESEM results, the uniform microstructure was observed, indicating that the addition of lignin did not affect the worm structure of bitumen. Based on the FTIR test results, lignin-modified bitumen showed that a lower number of carbonyl and sulfoxide compounds were generated after aging than for neat bitumen. Based on the linear amplitude sweep (LAS) results, the addition of lignin slightly reduced the fatigue life of bitumen. From the frequency sweep results, it showed that lignin in bitumen acts as a modifier since the physical interaction between lignin and bitumen predominantly affects the material rheology. Overall, lignin could be a promising anti-oxidant due to its economic and environmental benefits.@en

The chemical irreversible hardening of epoxy modified bitumen is affected by various physical factors and the successful application of this technology is directly linked with full understanding of chemo-rheological material characteristics. This study proposes a model to describe the material viscosity evolution during hardening of epoxy modified bitumen. The findings from numerical analyses performed to assess the mechanical response of epoxy modified bituminous binders are presented. Information of the chemical interaction of epoxy within a bituminous matrix was collected and all the influential factors have been determined. The proposed chemo-rheological model accounting for the polymerization of the epoxy in the bitumen was formulated and the sensitivity of material parameters, such as activation energy, reaction order and extent of hardening reaction until the gel point of epoxy modified binders, was demonstrated. Results of the analyses suggest that lower levels of activation energy increase the degree of hardening and the rate of viscosity development. By decreasing the hardening reaction until the gel point the achieved viscosity of epoxy modified bitumen was increased showing the importance of gel reaction extent on material viscosity evolution. The numerical studies have shown also that the polymerization rate in the epoxy modified bitumen is highly dependent on the temperature under various (non-) isothermal conditions. Also, the polymerization rate should be considered through all the material curing processes to avoid unwanted variations in the mechanical properties.

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Epoxy modified bitumen (EMB) is a promising technology for long lasting paving materials ensuring higher resistance to rutting, oxygen- and moisture-induced damage. In this paper, an analysis of the chemical reactions that take place during the chemical hardening process (curing) of epoxy modified bitumen
was conducted by means of Fourier Transform Infrared (FT-IR) spectrometer. For various amount of epoxy resin modification in bitumen, the hardening process was evaluated under various conditions. The fluctuation of the most crucial chemical groups occurring during the hardening process was identified and discussed. After the interpretation of chemical hardening, the critical hardening conditions were determined and fatigue tests were performed by Dynamic Shear Rheometer (DSR). Comparison with the unmodified bitumen shows that the fatigue resistance of epoxy modified binders improved significantly with increasing the amount of the epoxy resin in bitumen.@en

This research presents the implementation of a finite element model analysis for assessing the potential of utilizing alternative fibers for the development of inductive bituminous mixes with lower total weight, higher resistance against corrosion, and sufficient induction heating efficiency. Aluminum fibers are selected as the metallic modifier in bituminous mixes against the commonly applied steel fibers in order to develop inductive materials. The main reasons for applying aluminum fibers in bituminous mixes are presented in (Pavlatos et al., Framework for replacing steel with aluminum fibers in bituminous mixes, Advances in Materials and Pavement Performance Prediction, Submitted, 2018). A real fiber modified bituminous specimen is reconstructed by means of CT scans and its effective electrical conductivity is calculated assuming steel and aluminum fibers. Since steel fiber modified bituminous mixes have already been used successfully for induction heating, the aim of this work is to demonstrate that aluminum fiber modified bituminous mixes exhibit equally good properties as the steel fiber modified bituminous mixes for induction heating.@en

Induction assisted chemical hardening (curing) or induction hardening is a novel in situ hardening technique for thermoset modified bituminous materials that maintains most of the advantages of natural chemical hardening while eliminating the possible restrictions of longer curing times at lower temperatures. In particular, induction heating can be utilized to accelerate the polymerization of thermoset modified bituminous paving mixes in which inductive particles are added. In this study, steel fibres are dispersed in a thermoset bituminous system and during exposure to an alternating magnetic field, they are induction heated leading to a more rapid initiation of the polymerization. The non-isothermal hardening performance of fast reacting thermoset-bitumen is modelled during the thermoset crosslinking. The model can also be utilized to predict reaction kinetics and viscosity evolution in this material, thereby indicating that induction hardening represents a reliable polymerization method and can be utilized to cure thermoset bituminous materials. @en

Asphaltic mixes are self-healing materials since they have the capacity to close internal microcracks at higher temperatures or under external force. To trigger their self-healing, asphalt mixes modified with inductive agents can be heated and in that way healed through applying alternating magnetic fields with the aid of an induction coil and this technique is named induction healing. This paper assesses the potential of implementing induction healing in an existing asphalt pavement with steel slag. Cores have been drilled from a field section of a mix with steel slag and were fatigue damaged in an indirect tensile test and healed via induction. The material induction healing potential has been visualized through different X-ray CT scans over the thickness of samples. The induction heating speed of asphalt mixes with steel slag was evaluated as well. The main conclusion in this study was that the total fatigue life of asphalt with steel slag can be enhanced with induction heating. The efficiency of micro-cracks closure was the same over the thickness of asphalt mixes and in combination with the high heating speed (~1.8 °C /sec), induction becomes a very promising alternative for various pavement operations. @en

Remarkable variances were observed in permanent deformation curves of a dense asphalt mixture captured in triaxial repeated load permanent deformation (TRLPD) tests. In order to explore the causes of such variances, each permanent deformation curve was characterized firstly by an indicator (B) of the permanent deformation rate at a steady state stage. Meanwhile, a linear relationship was found between the values of indicator B and the resilient moduli of specimens after 1000 load repetitions. Secondly, a profound discussion on the potential relationship between resilient moduli and air voids content was performed. The discussion showed that air voids content appears to have no contributions to the observed variances. Nevertheless, three failure modes, tension failure, shear failure and shear failure with barreling, were observed in the X-ray Computed Tomography (CT) images of failed specimens subjected to triaxial compressive stresses. Furthermore, a significant correlation between failure modes and the resilient moduli was found by means of one-way analysis of variance (ANOVA). Moreover, it was found that the internal weak zones observed in the CT images of intact specimens dominate the behavior of the permanent deformation of asphalt mixture and the internal structure is the essential cause of such variances in the case of this study. This exploration highlights the influence of the internal structure on the mechanical performance of asphalt materials and thus recommends that considerable attention should be paid on the internal structure other than the volumetric properties when selecting test specimens.

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Noise produced from the tyre-road surface interface is one of the most important contributions to the overall traffic noise and there is an increasing requirement for predicting the tyre-road noise levels prior to road construction in the Netherlands. In practice, a model with a simple structure as well as a high accuracy is applicable in road engineering. Also, material properties are preferred to be used as input variables of the prediction model, which will facilitate the pavement design. Based on these considerations, models are developed for evaluating the tyre-road noise from the asphalt mixture compositions and road surface characteristics. They are statistical models developed from the measurements on thin layer surfacings in the Netherlands. Different regression methods, model types and input variable combinations are taken into account. The selection of the model is due to the fitness of the prediction and validation by using measurement data from in service road sections. Two models, which evaluate the tyre-road noise level from the surface characteristics and from material properties, respectively, are finally selected. By using these models, only a small number of input variables are required and reliable predictions can be provided. The models achieved in this study can be used for predicting the tyre-road noise generation in road engineering and investigating the influence of surface characteristics and material properties on tyre- road noise levels.

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Durable, therefore sustainable, road needs to attain specific characteristics, among others, resistance to permanent deformation and cracking. Determining the development of both characteristics are important to be able to predict pavement life and performance. In this research, permanent deformation occurring in three pavement sections was measured by a transverse profilograph. The pavement sections were simple two layer structures consisting of a gravel asphalt concrete (GAC) layer on a sand subgrade. The length and the width of the section are 16 m and 4 m respectively. These three sections were tested by means of Lintrack, an Accelerated Pavement Test (APT) which allows large number of realistic wheel load applied in a limited period of time. The results of this measurements shows the development of permanent deformation, which is defined as 'rut depth', as function of the number of load repetitions. Using relation exists between the radius of curvature of a deflection profile and the tensile strain at the bottom of a slab, the creep/permanent strain as a result of permanent deformation was calculated. This paper is carried out to determine relations between the rut depth and the radius of curvature and between the rut depth and the creep/permanent strain. Also, cracking development was observed upon these three pavement section. The result shows that there is a rather good correlation between rut depth and permanent/creep strain which is independent of the layer thickness.@en