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With circularity in mind, adding reclaimed asphalt in new asphalt mixtures is a common practice. While aiming for higher recycling rates, the need for better control of the mixture performance increases. Recycling agents are often proposed to restore the properties of aged binders. This study investigates the mechanical performance of plant-produced hot mix asphalt for base layers with high reclaimed asphalt content and recycling agents. Two field test tracks, each containing a section with and without a recycling agent, were constructed to allow for long-term performance evaluation. Plant-produced asphalt mixture from all sections was sampled and compacted in the laboratory and subjected to various mechanical tests, including rutting, stiffness, fatigue, cracking and water sensitivity. Besides a lower indirect tensile strength, the overall results indicate a limited influence of the used recycling agents on the mechanical performance of the mixtures, particularly in terms of resistance to rutting and fatigue cracking.

Cold in-situ recycling with foamed bitumen has become one of the most cost-effective and sustainable technologies due to working with low heating energy, less transport, and decreasing the use of new materials. This paper presents a benchmark laboratory study of the volumetric and mechanical properties of cold recycled foamed bitumen mixes blended with 100% reclaimed asphalt pavement (RAP) in the granular base layer. The air void content, indirect tensile strength, and resistance to moisture damage are tested to evaluate the impact of active filler, compaction technique, and geopolymer. It was found that the addition of active filler, regardless of the type, increased the moisture resistance between 30% and 35% compared to the mixture with no active filler. Moreover, the addition of slag-based geopolymer resulted in a substantial increase in tensile strength from 434 kPa to 823 kPa while leading to a sharp decrease from 70% to 38% in moisture resistance.

The demand for durability and resilience in asphalt pavements has led to the progressive implementation of performance-enhancing technologies like bitumen modification using polymers or fibers. This is particularly important in a port environment, where roads are subjected to heavy traffic. The main objective of this study is to contribute to the current state of knowledge on the performance of asphalt mixtures, including polymers and fibers, by conducting a comprehensive laboratory investigation of eight field mixtures, followed by an evaluation of their expected performance in five test sections using the AASHTOWare Pavement ME Design software. The eight mixtures included two lean asphalt mixes to be used as a replacement for granular layers, three base mixtures, and three surface mixtures. Laboratory testing showed that the addition of a blend of 91% polypropylene and 9% glass fibers increased stiffness and resistance to moisture damage. Also, this fiber blend improved cracking resistance when used in a relatively flexible mixture. It was found that top-down cracking predictions followed the trend observed in semicircular bending tests. Conversely, the predicted rutting performance did not align with the rut depth trend in the laboratory. Furthermore, the use of SMA instead of a dense-graded surface layer appeared to increase fatigue cracking in pavement sections with granular bases unless a high-modulus base asphalt layer was used. This study was a first attempt to use advanced pavement performance predictions in Belgium. The data gathered during the future monitoring of the test sections built as part of this study will provide valuable primary data for the local calibration of pavement distress models.

In an attempt to mimic the in-situ ageing of asphalt pavements, the exploration of appropriate laboratory ageing simulations has led to multiple standards on binder level. On asphalt mixture level, however, less consensus exists regarding ageing simulation protocols. This study aims to compare the chemo-rheological performance of bitumen between lab ageing protocols for binders, compacted and loose asphalt mixtures. A bituminous binder was used in bitumen ageing protocols, while it was also used to produce an AC10 mixture that was conditioned as a loose mixture and for compacted cylinders and slabs. Oven ageing of the mixtures was conducted for up to 9 days at 85 °C. The binder testing results, derived from empirical, rheological and chemical tests, indicate that 20 h of PAV ageing yields approximately similar results as 1–2 days of loose mixture oven ageing. Furthermore, in compacted samples, only the outer edge was influenced significantly by oxidative ageing.

Increased environmental awareness has led road agencies to consider the implementation of green public procurement (GPP). Besides sustainability rating systems, environmental indicators can also be implemented in GPP to help road agencies make informed decisions about the environmental impact of the pavement works they procure. A vast literature review revealed that it is still unclear which impact categories are responsible for the majority of the total environmental impact of asphalt mixtures. The objective of this study was to identify the impact categories with the greatest contribution to the total environmental impact of hot mix asphalt so that they can be implemented in the form of environmental indicators in GPP. The scope included conventional and polymer-modified binder and three mix design alternatives: only virgin aggregate, reclaimed asphalt pavement (RAP), and RAP with rejuvenators. The cradle-to-cradle life cycle assessment (LCA) performed showed that global warming (GW), fine particulate matter formation, fossil resource scarcity, and human non-carcinogenic toxicity were responsible for at least 90% of the total impact according to the ReCiPe 2016 hierarchic assessment method. Therefore, a simplified LCA focusing on these four impact categories seems sufficient for the purpose of comparing the environmental performance of alternatives in GPP. It was also found that GW alone accounted for approximately 50% of the total impact, which seems to make GW a good surrogate for the total impact among the asphalt mixtures evaluated. Future work should investigate whether the conclusions from this study still hold up when using secondary materials, lower temperature mixing technologies, or in-situ recycling.

Recent studies have highlighted the factors influencing the thermal performance of Pavement Solar Collectors (PSC), such as thermophysical properties of materials, geometrical specifications, and operational conditions. The present study introduces a new approach to investigating the impact of various parameters on the long-term performance of PSCs. The Response Surface Methodology (RSM) is used to optimise the experimental design by reducing the number of simulations resulting from the combination of several design parameters and ample design space. Hence, the proposed PSC system design aims to: i) assess the heat extraction capacity; ii) investigate the ability to diminish the asphalt surface temperature (STR); and iii) determine the reduction in asphalt layers’ rutting potential (RTR), through a coupled RSM and Finite Element (FE) simulation framework. The proposed statistical prediction regression models for heat harvesting capacity, STR, and RTR, adequately represent the experimental data with predicted R2 values above 0.95. The pipe spacing, flow rate, and inlet supply temperature show a high sensitivity to the objective functions, while other parameters display a less sensitive response. Finally, a multi-objective optimisation framework using the NSGA-II is proposed to seek a Pareto front solution in the design space, considering different (or equal) weights for the objective functions.

In recent years, harvesting solar energy as a renewable and sustainable energy source has been studied extensively across engineering fields. Having reviewed more than 50 large-scale projects of Hydronic Asphalt Pavement (HAP), this paper offers a series of findings: the range of construction cost of asphalt collector varies between 25 and 151 €/m2 and 1.760–3.000 €/m2 for the heat exchanger and the total cost. The energy harvest capacity of asphalt solar collector systems (0,6–0,8 GJ/m2/year) and the required amount of heat for snow melting projects (100–900 W/m2) vary significantly in different projects. Using grid supports for easier pipe placement and protection of pipes against heavy loads during and after construction is recommended. Pavement solar collector systems reduced carbon dioxide emissions by 8–100% in different projects by changing their source of energy from fossil fuels to renewable and sustainable sources. Moreover, in order to further evaluate the sustainability of the HAP systems, a detailed life cycle assessment is required, including all available data related to the energy performance, pavement service life, material end-of-life recycling, etc. Finally, the paper identifies the knowledge gaps requiring further research especially in the area of energy output of the HAP systems, pavement service life and life cycle assessment.

To cope with the global climate crisis and assist in achieving the carbon neutrality, the use of biomass materials to fully or partially replace petroleum-based products and unrenewable resources is expected to become a widespread solution. Based on the analysis of the existing literature, this paper firstly classified biomass materials with potential application prospects in pavement engineering according to their application and summarized their respective preparation methods and characteristics. The pavement performance of asphalt mixtures with biomass materials was analyzed and summarized, and the economic and environmental benefits of bio-asphalt binder were evaluated. The analysis shows that pavement biomass materials with potential for practical appli-cation can be divided into three categories: bio-oil, bio-fiber, and bio-filler. Adding bio-oil to modify or extend the virgin asphalt binder can mostly improve the low temperature performance of asphalt binder. Adding styrene-butadienestyrene (SBS) or other preferable bio-components for composite modification will have a further improved effect. Most of the asphalt mixtures prepared by using bio-oil modified asphalt binders have improved the low temperature crack resistance and fatigue resistance of asphalt mixtures, but the high tem-perature stability and moisture resistance may decrease. As a rejuvenator, most bio-oils can restore the high and low temperature performance of aged asphalt and recycled asphalt mixture, and improve fatigue resistance. Adding bio-fiber could significantly improve the high temperature stability, low temperature crack resistance and moisture resistance of asphalt mixtures. Biochar as a bio-filler can slow down the asphalt aging process and some other bio-fillers can improve the high temperature stability and fatigue resistance of asphalt binders. Through calculation, it is found that the cost performance of bio-asphalt has the ability to surpass conventional asphalt and has economic benefits. The use of biomass materials for pavements not only reduces pollutants, but also reduces the dependence on petroleum-based products. It has significant environmental benefits and development potential.

Incorporating reclaimed asphalt (RA) in surface layer mixtures is still limited due to performance concerns, and it becomes even more challenging when combining aged polymer-modified bitumen (PMB) with virgin PMB. This study aims to evaluate, from a binder perspective, the feasibility of incorporating reclaimed polymer-modified binder (RPMB) in new surface layer mixtures. To address this challenge, blends of RPMB and virgin PMB were investigated at three replacement rates (20%, 40% and 60%) with and without a tall oil-based rejuvenator. First, the viscoelastic behaviour of the blends was assessed using a dynamic shear rheometer. Moreover, physicochemical changes were tracked using infrared spectroscopy and fluorescence microscopy. The experimental investigation revealed that, due to polymer degradation of the RMPB, only the blends with 20% RMPB exhibited polymer activity. Finally, the use of the rejuvenator compensated for the rheological properties of the aged RPMB and reduced the susceptibility to non-load-associated cracking.

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.

This paper evaluates the performance of fiber-reinforced mixtures subjected to moisture damage. Response Surface Method was used to design an experimental matrix based on the central composite design. The amounts of fibers, number of freeze and thaw cycles, and testing temperatures were considered as factors, while maximum load, stiffness, indirect tensile strength, CT index, fragility index, broken aggregate, and adhesion failure were regarded as the responses. Indirect tensile strength test and 3D image analysis were conducted to characterize mixtures’ fracture properties and moisture susceptibility, respectively. The results show that temperature exhibits the highest influence on mixtures’ mechanical properties as well as adhesion and cohesion failures. An increase in the number of freeze and thaw cycles deteriorated the mixtures’ performance. Although higher beneficial impacts of glass fiber were reported earlier, this study proved that the performance of the mixtures prepared with combined fibers is comparable with the previous study. This finding brings forth the advantage in cost reduction of reinforced mixtures production due to the replacement of part of the glass fiber with polypropylene fiber. In addition, it was found that a combination of utilized fibers up to approximately 0.2% by weight of aggregates exhibited beneficial impacts on load bearing capacity, indirect tensile strength, and proportion of broken aggregate while exceeding this amount was not favorable which was correlated to the jeopardizing of cohesion level between mixtures constituents. Moreover, it was observed that fibers slightly reduced the fragility index by obstructing crack propagation. It was finally concluded that a higher amount of fibers enhanced mixtures' moisture resistance and diminish the negative effects of freeze and thaw cycles.

Solar energy harvesting as a renewable and sustainable energy source has been widely investigated in recent years across engineering fields. The use of Pavement Solar Collectors (PSC) can lead to clean energy production, an increase in road safety, prolong the service life of asphalt pavement, and can mitigate the Urban Heat Island (UHI) effect. This study describes a controllable large-scale research PSC prototype with high configuration flexibility, and full monitoring capability at the University of Antwerp, Belgium. Since small- or laboratory-scale setups do not reflect the behavior of actual projects, the present paper investigates the thermal response of a large-scale PSC in the Western European climate, including heating load, heat extraction capacity, and asphalt surface and profile temperature changes during heating and cooling experiments. The study shows that a low supply temperature compared to high (14 °C vs. 28 °C) can reduce the depletion rate of the stored thermal energy in borehole thermal energy storage up to 7 times. The sensitivity analysis indicates that an increase in flow rate from laminar to transient regime requires twice as much thermal power compared to the same flow rate changes within transient and turbulent regimes. The maximum average daily efficiency of the PSC could reach 34% with a flow rate of 4 l/min. The experimental results showed that increasing the pipe length from 50 m to 200 m reduces the cumulative power extraction capacity by up to 48%. Furthermore, the PSC system shows great potential in reducing the asphalt surface temperature (up to 12 °C) to mitigate the UHI effects. Finally, the PSC system effectively controls the temperatures of the interface zones to reduce the rutting distress in the summertime and lower the potential of cold thermal crack developments and brittle shear failure behavior in wintertime.

Fatigue resistance is of paramount importance for bituminous materials and so it is the effect of applying rest periods, as this is a more realistic representation of the traffic loading. To this end, to evaluate the healing potential, storage rest periods were introduced during a series of fatigue tests. In this study, the healing investigation was performed on the asphalt and mortar scale, aiming to assess the effect of reclaimed asphalt binder (RAB) on the healing potential. For the mortars, the healing indices derived under different damage levels and rest periods were modelled into a healing master curve, describing the healing index as a function of damage level and rest time. The asphalt tests revealed that the mixtures containing RAB showed higher healing potential compared to the control mix, attributed mainly to the existence of a softer blend as a result of partial blending. Furthermore, chemical indicators were considered to assess the healing potential of the binder blends and compared to the results of the healing tests. For the mortars, the 70% RAB samples showed the lowest healing potential, reflecting the full effect of very high RAB content, when the RAB is fully blended with the virgin binder.

The ageing of bitumen has received great attention both from a chemical and rheological perspective due to its direct impact on asphalt performance. However, open questions with respect to the convergence of the synchronous ageing changes in rheology and chemistry of bitumen still exist. This paper addresses these alterations of chemistry and rheology and attempts to establish a link via fitting rheological equations fed by fundamental chemical information. To that end, three binders of different type were used in four different laboratory ageing states. A number of spectroscopic techniques and rheological testing were employed to derive corresponding chemical and rheological parameters. In parallel, various statistical methods (Bivariate analysis, Wilcoxon test, Factor analysis) assisted in identifying relationships among the chemo-rheological parameters and simplifying the number of variables. The results of this study demonstrate that chemistry and rheology are following similar changes when considering laboratory ageing following the fast-rate phase of a dual oxidation scheme and short-term lab ageing. Finally, this work manages to establish a linking framework for a number of newly-introduced rheological parameters. All in all, the results of this study might be particularly interesting for future interventions in the chemical composition of bitumen, considering its effect on performance.

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.

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.

Currently, reclaimed asphalt (RA) is considered as one of the most recyclable materials in the construction industry of the developed countries. The purpose of this paper is to investigate the effect of RA on manufactured mixtures in Flanders and to define a correlation between RA and mechanical performance through the statistical spectrum. In this study a statistical analysis was carried out on a dataset of 74 bituminous mixtures, certified in Flanders (2009–2016). A bivariate correlation analysis was used to determine the influential factors and the impact on the performance of mixtures. In addition, the determination of the effect of RA on major mechanical properties was evaluated by an independent-samples T-test analysis. Finally, a prediction model was fitted using the multiple linear regression analysis. The main result of the comparison within the mechanical properties showed that for this dataset the mixtures with RA exhibit at least equal mechanical properties compared to mixtures without RA. The correlation analysis provided insight on the influential factors of the mechanical properties, such as a significant linear correlation between binder properties (penetration and softening point) and mechanical properties (stiffness, fatigue and wheel rutting). Moreover, the multiple linear regression (MLR) analysis quantitatively described the influence of mix properties on mechanical properties.

The authors wish to make the following corrections to this paper [...]

An improved test is proposed to determine the fatigue resistance of bituminous mortars by applying time-sweep cyclic (oscillatory) tests using a dynamic shear rheometer (DSR). To evaluate its applicability, a bituminous mortar mixture derived from a dense asphalt concrete (AC) mix was utilized. The objectives of this study were twofold; firstly, to design a new geometry that ensures higher repeatability of measurements and failure at a predefined zone. Secondly, to provide a methodology to evaluate the fatigue resistance of a mortar sample including the theoretical design of the mortar composition and the actual fatigue test protocol. The findings of this study present an efficient test procedure for the estimation of the fatigue life of bituminous mortars, with a consistent fracture zone, reproducible mortar samples and high coefficient of determination (R2) for the fatigue curves. Reflecting on other fatigue testing approaches, this theoretical and empirical study provides additional value towards standardization of fatigue testing in bituminous mortars.

In this study, an innovative methodology is proposed to characterize the short-term aging of asphalt binders using the matrix analysis method. The rotational viscosity and complex shear modulus of asphalt binders were chosen as target rheological properties for the analysis of aging. A set of square matrices was developed based on test temperatures and the synthetic additive wax content. Transformational short-term aging matrices were obtained that characterize the trend of the aging process as a function of binder type, temperature sweep, and additive percentage. The results of the matrix analysis show that the trend of short-term aging depends on the binder performance grade and the rheological characteristic chosen for the analysis of aging. In addition, transformational aging matrices can provide detailed information about the range of the aging rate and the trend in aging for each binder type. Furthermore, the components of the transformational matrices clearly show the sensitivity of the binders to aging. In conclusion, the matrix analysis of aging can be used to compare the effects of short-term aging of different asphalt binders.

The assessment of thermal performance and efficiency of the Pavement Solar Collector (PSC) systems is essential in designing such systems. In this paper, a simplified simulation model is developed to predict PSC's performance at the design stage. Due to its simplicity, accuracy, and extremely quick simulation run-time, the model output can be linked with other thermal models and renewable heat sources to apply real-time changes in the PSC systems and used in the automation of a PID-controller. The output results show good compatibility between the predicted and simulated data, where the relative error values for model parametrization and validation are less than 0.21% and 0.5%. In terms of computational cost, a yearly long-term performance run time of the present model was simply 3 s (without parametrization), 300,000 times faster than a FEM model for only one month. A systematic sensitivity analysis on different design parameters shows that the efficiency index increases with an increase in pipe spacing, pipe embedment depth, and flow rate, while it decreases with an increase in the asphalt thermal conductivity in the wintertime. Also, the variation of the heat transfer coefficient UA* and correlation parameter k in different PSC configurations was established.

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.

The impact of aging on asphalt binder depends on multiple factors including binder type and environmental conditions. In a previous study, Shalaby proposed two empirical equations to investigate the effects of extended short-term aging on the shear modulus and phase angle of asphalt binders. The objective of this study was to use a robust mathematical approach based on an artificial neural network (ANN) to validate the empirical approach proposed by Shalaby to model short-term aging of asphalt binders. Both methods were compared in terms of percent error, root mean squared error, and plots of predicted versus measured values for four different binders. The results showed that Shalaby’s equations exhibited sufficient accuracy to predict the effect of aging duration and temperature on the shear modulus and phase angle of asphalt binder. Furthermore, this study showed that Shalaby’s approach can be employed to estimate the increase in high-temperature true grade as a result of extended aging. Therefore, the approach provides designers with a tool to make informed decisions regarding binder type selection. In particular, such a method can be utilized when extended aging durations resulting from construction delays or extended hauling distances are expected in the field.

The fatigue resistance, as a performance indicator, is of paramount importance for the selection and benchmarking of bituminous materials. The bituminous mortar can be considered as the medium that connects and envelopes the coarse aggregate skeleton, and hence will significantly influence the fatigue resistance at bulk-scale. Therefore this study presents the steps and challenges of a new testing framework to evaluate the fatigue resistance of bituminous mortars. To do so, first, a new test geometry is introduced, which will ensure cohesive failure in a predefined area. The integrity of this sample geometry is assessed theoretically through finite element simulations and by computer tomography scans. Secondly, specimens of the new geometry are evaluated experimentally using a dynamic shear rheometer, where time-sweep tests are performed on two control mortar types under various test conditions. The control mortar types are fabricated using two commercial bituminous binders, one modified and one neat binder, to evaluate the effect of binder type. The test results are comprehensively analysed using fundamental dissipated energy-based concepts but also empirical and phenomenological failure criteria, providing insights into the failure evolution. For the tested mortar types, the analysis shows good convergence with the considered fatigue models. Finally, using dissipated energy concepts led to the most consisted fatigue model, which is independent of binder type and test conditions.

At the end of their service life, asphalt pavements exhibit distresses such as cracking and ravelling due to the aged bituminous binder. The recycling process of reclaimed asphalt should compensate for the deteriorated binder properties. The main objective of this binder study is to compare two common recycling strategies: the use of a softer binder and a rejuvenator. Three recycling percentages, 0%, 40% and 70% of reclaimed asphalt binder were evaluated. All binder blends were prepared with similar penetration and softening point values. In order to simulate binder performance during service life, ageing protocols by means of rolling thin film oven test and pressure ageing vessel were performed. The investigation included both mechanical and chemical tests. A dynamic shear rheometer was used to assess different rheological parameters over an extensive temperature range. Linear amplitude sweep tests were performed to estimate the fatigue resistance at intermediate temperatures. Resistance to permanent deformation was assessed with a multiple stress creep recovery test. Fourier-transform infrared spectroscopy was used to assess the formation of bonds that indicate oxidative ageing after the ageing protocols. Moreover, an optimised method was introduced to calculate the carbonyl index for rejuvenated binders, which also allows to detect the presence of a rejuvenator in a bituminous binder. The results show that the inclusion of rejuvenator results in similar rheological behaviour compared to the application of a soft binder. Furthermore, the rejuvenator improves binder fatigue life without reducing the performance at elevated temperatures.

The road industry is confronted with the search for new materials and means to lower their economic impact as well as better/more accurate evaluation methods. Life cycle cost analysis (LCCA) has been of great interest as it is a useful tool in assisting road agencies to make better investment decisions. Furthermore, using reclaimed asphalt pavement (RAP) has shown to be a viable option to reduce virgin material use and to lessen the economic impact of the asphalt industry. However, literature shows that previous research often does not adjust service life (SL) in LCCA calculations when considering different design alternatives (e.g., varying RAP content), even though mechanical tests clearly exhibit a difference in performance. The main objective of this study consists of two parts: 1) to evaluate the effect of multiple RAP contents on the SL of asphalt base layers, and 2) to compare the LCCA of asphalt base layers when using a fixed or variable SL. Five AC14 asphalt base alternatives with varying recycling rates (0%, 20%, 40%, 60%, and 80% RAP) were designed. The predicted SLs increased with increasing RAP content and varied between 21 years and 27 years, while the reference SL for an asphalt base layer is typically considered as 20 years. After implementing this adjusted SL in an LCCA, it was concluded that a fixed SL of 20 years overestimated the net present value (NPV) by 3% to 18%. Furthermore, the total NPV decreased by 13% to 53% when using 20% to 80% RAP, respectively

With the increased use of reclaimed asphalt (RA), the ability of bituminous materials to resist fatigue cracking may face a decline mainly due to the aged reclaimed asphalt binder (RAB), especially when RA is used at higher rates and not sufficiently treated. In this study, the bulk scale (asphalt) and its subscale (mortar) were employed to evaluate the effect on fatigue resistance when a RAB is added, by considering three replacement rates: 0%, 40%, and 70% RAB. The fatigue testing of asphalt mixtures was carried out using a four-point bending (4PB) setup, while the mortars were tested using a new column-like geometry utilising a dynamic shear rheometer (DSR). The fatigue properties were further analysed using dissipated energy concepts. The aim of this study was, first, to assess whether the inclusion of a RAB can provide at least similar fatigue properties compared to an all-virgin mix, and second, to evaluate whether the proposed treatment is beneficial for the mixtures with a RAB. The asphalt tests revealed that the inclusion of a 40% RAB led to increased fatigue resistance, whereas the mortar tests showed that the inclusion of RAB has an inverse effect on fatigue life.

Bitumen is one of the most important materials used in roads. During asphalt pavement construction, workers can be affected by emissions, such as volatile organic compounds (VOCs), when bitumen is heated. Therefore, it is crucial to correctly identify and measure VOCs. This paper presents a novel, promising method to determine VOC emissions. The proposed method offers a way to standardize routine measurements on a lab scale, enabling reliable comparison across bitumen types and their modifications or additives. A proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) was used to monitor VOC emissions from commercial unmodified bitumen and crumb rubber modified bitumen (CRMB) with heating of up to 180 °C. Results confirmed that the temperature range of 160–180 °C is a highly influential factor for VOC emissions from heated commercial bitumen and particularly CRMB. A significant increase in alkane and aromatic emission was detected when the binders were heated to 180 °C. Sulfur-containing VOCs were almost nonexistent for the base bitumen fumes, while a significant increase was detected in the fumes when two different types of CR were added to the bitumen, even at 120 °C. The additional CR in the bituminous binder contributed to the potentially harmful VOC emission of benzothiazole, which belongs to the class of sulfur-containing compounds. The concentration of benzothiazole was 65%, 38%, and 35% higher for CR1 in comparison to CR2 at 140, 160, and 180 °C, respectively. It is clear from the results that this method allows different bitumen sources or modifications to be quickly analyzed and their VOC emissions cross-compared. If adopted and confirmed further, the method could offer the asphalt industry a viable solution to monitor VOC emissions by analyzing samples in real time at different steps of the production process.

Several factors affect asphalt binder and mixture characteristics. This makes pavement performance assessment a mounting task. This paper evaluates the effects of short-term aging on compactibility and volumetric properties of asphalt mixtures using the Response Surface Method (RSM). Three different binders were utilized to produce mixtures (type AC-14). Aging temperature, aging duration, and duration in a climate chamber with increased humidity and ultraviolet lighting were considered as independent variables (IV), while compactibility and volumetric properties were regarded as dependent variables (DV). The findings revealed significant impacts of aging temperature and duration on compactibility, air voids, voids in mineral aggregate, and voids filled with asphalt, while duration in the climate chamber exhibited no significant influence on the DVs. The effects of IVs on DVs varied by binder type. This was achieved through an elaborate statistical analysis. The study, finally, demonstrates the RSM&rsquo, s potential to predict changes in responses from mathematical equations&mdash, converging with the experimental observation&mdash, with excellent accuracy. Potentially, pavement contractors can use this method by replacing haulage duration and mixtures&rsquo, temperatures during paving in the developed models. It enables them to predict the pavement density and adjust pressure as well as the number of roller passes to achieve the desired requirements.

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.

Bitumen, also called asphalt binder, is the key component in asphalt mixtures. Studies to investigate the microstructure of this material show a rich morphology, especially the formation of bee structures in bitumen containing wax. Most research in this field has investigated these microstructures using commercial image processing software that needs a manual selection of these patterns to obtain certain characteristics. This study aims to construct a deep-learning-based object-detection model that can detect these bee patterns in the images acquired from bitumen samples using Confocal Laser Scanning Microscopy (CLSM). The CLSM images are then used to determine the morphological properties of the samples. The properties investigated are some typical roughness parameters and the wavelength calculated by a novel image processing technique based on the two-dimensional fast Fourier transform. In addition, these developed methodologies are used to investigate the influence of short-term and long-term ageing on the microstructure of a waxy bitumen. The results show that the trained deep learning model can be used to successfully detect the location, number, and area of the bee structures. The number of bee patterns and the area of the surface they cover are reduced upon ageing. Furthermore, some strong trends are found between the computed roughness parameters and the ageing level of the samples. Finally, the estimated wavelength of the bee patterns increases by ageing bitumen. The successful development and demonstration of these methods show their great potential in analyzing the microscopic images of bitumen taken by CLSM or atomic force microscopy and the enormous opportunities for future research.

Molecular dynamics is used to simulate the self-healing process of asphalts mixed with a healing agent. Sulfoxide functional groups were introduced into the virgin asphalt to produce a short-term-aged asphalt model. The model is validated by comparing density, diffusion coefficient, solubility parameter, and viscosity with real measurements. Plant oil and Aromatic oil are chosen as typical healing agents. The molecular models of asphalt and healing agent are integrated into a micro-crack model, and the healing process is simulated with molecular dynamics. The results show that Plant oil is a better choice for improving the healing rate of virgin asphalt, while Aromatic oil is better for improving the healing rate of short-term aged asphalt. The higher the temperature is, the better effect the healing agent will have on the asphalt. Healing is maximized above 15 degrees C for virgin asphalt and above 45 degrees C for short-term-aged asphalt. Molecular simulations show that the healing process depends on the diffusion of the healing agent and asphalt into the micro-crack. After the crack is filled, bitumen and oil molecules continue to mix. Aromatic oil produces a better mixing that leads to a more uniform composition and better mechanical properties. (c) 2021 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.

In October 2017 a large-scale prototype for a Heat Exchanging Asphalt Layer (HEAL) was constructed in a cycling path, together with other innovative technologies, such as Fibre Bragg Gratings to monitor the stress and strains, and fiber-reinforced asphalt in the top layer. The HEAL prototype consists of 30 m², 8.5 m x 3.5 m, and includes four circuits of pipes, 50 m of length each, placed in a collector layer. Additionally, two boreholes with a depth of approximately 100 m have been installed next to the cycling path so that heat can be extracted from the HEAL during summer and is available during winter to keep the cycling path ice and snow-free. By using an additional heat pump an overall better efficiency will be obtained. Different sensors to monitor the temperature of the asphalt and fluid were installed, together with a weather station that captures the most important weather parameters, such as wind speed, outside temperature, solar radiation, … By changing the way the different circuits of pipes are connected, it is possible to investigate the influence of total pipe length and pipe layout. Also, the input temperature and flow rate of the water will be controlled and varied during the experiments. An overview of the complete design, including all sensors and electromechanical devices, is given in this paper. Furthermore, some details are included from an extended Finite Element Model which will be validated using the experimental results from the large-scale prototype.

Reclaimed asphalt pavement (RAP) has been increasingly used in the past few decades as a replacement of natural aggregates in pavement layers. However, low replacement level is employed, and consequently, large quantities of RAP are still left unused. Researchers often neglect foundation pavement layers, but it has higher prospects to consume recycled materials due to their increased thickness. RAP has inferior prop-erties compared to natural aggregates; therefore, cementitious binders are used to produce a (sub)base layer using high volumes of RAP. This paper reviews the use of RAP aggregates with cementitious materials for pavement foundation layers. Special attention is given to the use of alkali-activated materials (AAM) as a binder in substitution for Portland cement (PC). This review discussed the properties of fresh and hardened RAP in cementitious matrices, as well as changes in the microstructure. The biggest challenge on the use of RAP on both systems, RAP-PC and RAP-AAM, is the bond issues caused by the presence of asphalt on the surface of the aggregates. Some researches addressed how physical or chemical pre-treatments to the RAP could improve the adherence to the paste, but few studies focused on the optimisation of the binder. A literature survey indicated that an optimised mix design, durability studies and life cycle assessment (LCA) are important research needs towards the development of RAP-AAM. Despite the lack of research evidence, RAP-AAM is a promising solution for foundation pavement layers. (C) 2020 Elsevier Ltd. All rights reserved.