Pavement materials that could enhance the mechanical properties of open-graded porous asphalt mixtures in long-term service periods could offer a solution to produce long-life pavements, causing a reduction of interventions' needs, as well as the associated disruptions to road users and user costs. One option to improve the longevity of open-graded porous mixtures is with the use of epoxy asphalt that, despite its high initial cost, offers enhanced longevity that might offset any future user and intervention costs. This study aimed to evaluate the durability of plant-produced epoxy-modified open-graded porous asphalt mixtures. A batch production plant was employed to produce loose mixtures, which were used to pave a test road in the Province of Gelderland, the Netherlands, and compact specimens in the laboratory. Control mixtures with a non-epoxy-modified asphalt binder were also produced in the same plant. The durability of laboratory- and field-compacted mixtures was evaluated by conducting indirect tensile tests before and after oven conditioning. Results illustrated that the epoxy-modified asphalt demonstrated the highest strength and stiffness values, while the strength was reduced after conditioning in a water bath with the retained strength within the allowable specification limits. This attribute was confirmed from drill cores obtained from the test road after one year in service. Also, the materials compacted in the field had slightly higher strength and stiffness values than the laboratory-produced mixtures. Although the results provided have illustrated the improvement of durability of open-graded porous asphalt with implementing epoxy modification, further evidence from the test road over the years is needed for validation.

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This study presents finite element (FE) modelling of tire pavement interaction based on a micromechanical pavement surface. The FE model of the pavement surface is created using CT scan images of an actual pavement specimen to accurately represent the micromechanical surface morphology of the pavement. The micromechanical FE model of the pavement consists of aggregate, binder, and air voids. Using the micromechanical pavement model, tire pavement interaction simulations are performed using ABAQUS by setting binder and rubber as viscoelastic materials and aggregate as an elastic material. Moreover, the FE model includes layers of asphalt, base course, and subgrade to mimic a real pavement. The interaction between tire and the pavement surface is modelled via the surface-to-surface contact.

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Epoxy-asphalt (EA) attracted the attention of road authorities in many countries as a solution for open-graded porous surface layers with enhanced durability and longevity. This research presents an experimental programme to assess the durability of epoxy-modified open-graded porous asphalt (EMOGPA) mixes, emphasising the effects of the reactivity of two mineral fillers on mixes containing various EA proportions. Results indicate that the EMOGPA mixes have shown a high sensitivity to the conditioning time before compaction (aka. preconditioning). The materials produced exclusively by EA are the most sensitive to preconditioning, reducing their water and ravelling resistance with increased preconditioning time lengths. The number of gyrations has also been proven as an efficient quantity of the compaction effort required to reach the target mix properties. Moreover, the proportional increase of EA in mixes led to substantially improved durability. Hydrated lime in epoxy-modified asphalt mixes also affected their mechanical response. The indirect tensile strength and toughness of EA mixes were higher than other mixes, while mixes with limestones were stronger and tougher than those with hydrated lime. This attribute reflects the positive contribution of apolar fillers to strengthen and toughen the EA mixes.@en

Epoxy asphalt attracted the attention of road authorities in many countries as a solution for du-rable open-graded porous asphalt (OGPA) surface layers with enhanced longevity. Nevertheless, the recycla-bility of aged epoxy asphalt materials has not been thoroughly studied yet. This research presents an experi-mental program conducted in the laboratory to assess the potential recyclability of epoxy-modified open-graded porous asphalt (EMOGPA) mixes. Results indicate that the aging increased the tensile strength of studied mixes, with the strength and strength development rate of aging EMOGPA mixes to be almost identi-cal to standard OGPA mixes. The EMOGPA mixes have shown higher resistance against water damage than the OGPA mixes supporting the claim that the stone-mastic adhesion is improved with the use of epoxy bind-er. It was also proven that the aged material containing the epoxy binder could be re-melted to produce new pavement materials. The new EMOGPA mixes with the recycled epoxy material exhibited similar durability characteristics with the recycled standard OGPA mixes.@en

This research aims to evaluate the potential environmental impact of epoxy-modified asphalt used as a pavement material for roadways in the Netherlands and identify what determines the environmental performance of the epoxy asphalt technology through life cycle assessment. Results indicated that the incor-poration of epoxy binder in asphalt could lead to significantly lower environmental impact than the unmodi-fied asphalt. Such benefits are attributed by the minimal maintenance interventions of a pavement with epoxy and their remarkably higher service life over the analysis period. Finally, although the initial price of epoxy-modified asphalt production and construction was substantially higher than of standard asphalt mixtures, the overall score of epoxy-modified asphalt pavement in all weight scenarios was lower than that of the reference structures reflecting the sustainability benefits of using this technology for roadway pavements.@en

The structural evaluation of existing pavements forms the basis for formulating cost-effective maintenance and rehabilitation strategies. A promising tool for pavement structural evaluation at network level is the Traffic Speed Deflectometer (TSD) test. However, the application of the TSD test is hindered by the lack of a robust and efficient parameter identification technique. To solve this problem, a theoretical model for the TSD test is first formulated. Then, a minimisation algorithm which works best with the theoretical TSD model for parameter identification is selected. Finally, the performance of this combination in processing field TSD measurements is studied. The results show that the modified Levenberg-Marquardt algorithm using all the 9 detection points is most suitable to be combined with the theoretical TSD model for parameter identification, which gives a promising parameter identification technique for TSD tests of pavements. The presented work contributes to the development of technologies for pavement structural evaluation.

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Lignin, one of the most abundant natural polymers, has been extensively studied as an additive in bituminous binders. Even though the lignin improves the overall resistance against oxidative aging of bitumen, it could lead to high thermal cracking sensitivity. In this study, a bio-oil (i.e., rapeseed oil) is implemented in lignin-modified bitumen to ameliorate characteristics, such as the resistance to fatigue and cracking. The long-term aging of bitumens formulated by different proportions of bio-oil was simulated by the pressure aging vessel (PAV) method. Fourier Transform Infrared Spectroscopic (FTIR) results demonstrated lignin has a remarkable antiaging effect, but adding bio-oil will slightly deteriorate the antiaging effect. The Brookfield rotational viscometer showed that the addition of bio-oil was able to reduce the binder’s viscosity observably, thereby improving the workability of bitumen. The frequency sweep tests revealed that lignin increased the stiffness and improved the thermal stability. Also, the multiple stress creep recovery tests corroborated that lignin significantly enhanced the rutting resistance of binders. The fatigue and thermal cracking properties of lignin-modified binder could be strengthened by increasing bio-oil content which is confirmed from both linear amplitude sweep, Glover-Rowe parameter, and Bending Beam Rheometer (BBR) tests. Moreover, the relaxation test results demonstrated that bio-oil decreased the residual stress ratio and relaxation time dramatically. Overall, this study has shown preliminary conclusions on the incorporating of bio-oil to enhance the medium-low temperature properties of lignin-modified binders. In the meantime, bio-oil did not interfere with the improvement influence of lignin on the neat bitumen regarding high-temperature performance.@en

Crumb rubber modified bitumen (CRMB) can be regarded as a binary composite system in which swollen rubber particles are embedded in the bitumen matrix. Previous study has successfully implemented the micromechanics models in predicting the complex moduli of CRMB binders using more representative constituent parameters. In the regime of master curves, while the micromechanics models used predicted well in the high-frequency range, they underestimated the complex modulus in the low-frequency range. The current study aims to further improve the prediction accuracy of micromechanics models for CRMB by considering the interparticle interactions. To accomplish this goal, a new reinforcement mechanism called chain entanglement effect was introduced to account for the interparticle interaction effect. Results show that the polymer chain entanglement effect accounts for the underestimation of complex modulus and lack of elasticity (overestimation of phase angle) for CRMB at high temperatures/low frequencies. The mechanical properties of bitumen matrix and entangled polymer network can be determined based on the rubber content. The introduction of the entangled polymer network to the generalized self-consistent model significantly improved the prediction accuracy for both complex modulus and phase angle in the whole frequency range. In summary, by incorporating the physio-chemical interaction mechanism into the currently available models, a new dedicated micromechanics model for predicting the mechanical properties of CRMB has been developed. The predicted viscoelastic behaviors can thereafter be used as inputs for an improved mix design.@en

Pavement materials containing epoxy-asphalt are mainly used to enhance the fatigue cracking resistance of surfacing layers on bridges. These materials have also been proposed for roadways, but limited field data are available. In this research, a fully instrumented epoxy-modified asphalt surfacing layer was applied to measure strain responses in service conditions. Results over the first-year monitoring period indicated that the epoxy-modified asphalt behaves fundamentally similarly to a reference one with an asphalt mix of the same aggregate gradation. The epoxy-modified asphalt demonstrated the lowest transverse compressive strains at decreased temperatures, reflecting the potentially high material resistance against thermal cracking. After the summer period, the modified material showed lower tensile strains than the reference mix compared with the previous time period. Such an attribute could indicate the ongoing curing-induced stiffening of epoxy-modified asphalt at high temperatures during summer. The longitudinal and transverse strain measurements had inverse tendencies at all temperatures. Finally, the mechanical response of the studied materials after the summer has been examined using a classical fatigue cracking model and following a life cycle assessment methodology, and preliminary findings support the use of epoxy-asphalt for sustainable pavements.@en

Membranes of sufficient bonding characteristics could improve the integrity of the multi-layer structures on orthotropic steel deck bridges (OSBDs), enhancing thus the structural response of these systems and, ultimately, their service life. In this research, full-scale experiments were performed at the LINTRACK accelerated pavement testing facility of the Delft University of Technology to evaluate the performance of two surfacing systems commonly used in the Netherlands, giving emphasis on assessing the interface response of membranes with the surrounding materials. Results indicated that the tensile strains remain almost uniform at the top of porous asphalt, in both transverse and longitudinal directions, as no appreciable loss in stress-carrying capabilities was seen even at the end of the testing program. The sections exhibited similar behaviour in terms of strains, with some differences in strains indicating the impacts of membranes at interfaces. The importance of membranes of the desired bonding characteristics was also reflected by the relative displacement measurements. The relative interlayer slip had been higher in the transverse direction than the longitudinal one, with slightly higher displacements in one of the test sections. Overall, no cracking was observed on either section, and the current findings support the use of membranes between surfacing layers on OSBDs.

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Miscibility, and lack of it, is decisive for durable polymer-modified asphalt binders and reflects the long-term performance of asphalt materials in terms of fatigue and thermal cracking. In this work, the glass transition behavior of epoxy asphalt will be assessed extensively after different oxidative aging time periods using differential scanning calorimetry. The composition dependence of glass transition in epoxy asphalt binders over oxidative aging is evaluated by emphasizing the deviation of glass transition temperature (Tg) with the change in sign and magnitude. An entropy-based analysis of glass transitions in epoxy asphalt is discussed as well. The blends formulated by epoxy and asphalt binder have shown an increase of the Tg deviation from the ideal mixing rule over oxidative aging. Two different shapes of the composition dependence of the Tg values are observed between the blends with and without fillers but showing both distinct positive deviations from the case of mixing ideal materials. The Tg and heat capacity (Cp) parameters determined in relation to the epoxy asphalt composition provide insights into the effect of limestone fillers on the oxidation-induced embrittlement of epoxy asphalt materials. The results could help select the epoxy proportion in asphalt to develop super-durable and long-lasting pavement materials.@en

Rubberized asphaltic materials have been frequently combined with warm-mix asphalt technologies to tackle the issues of high energy consumptions and emissions during construction. Effective and accurate characterization of binder properties is conducive to the improvement of long-term pavement performance. The current study aims to quantify the effects of rubber content and warm-mix additives on rutting and thermal cracking performance of crumb rubber-modified bitumen (CRMB), and explore the rubber and additives modification mechanisms and their impacts on the binder performance. CRMBs containing different rubber contents and warm-mix additives after long-term aging were subject to multiple stress creep and recovery (MSCR) tests and low-temperature frequency sweep tests using a dynamic shear rheometer (DSR) with 4-mm loading plate to investigate the high- and low-temperature performance, respectively. Rheological tests were also conducted on the bitumen and rubber phases of CRMB to understand the rubber modification mechanism. Results show that CRMB binders have superior rutting and thermal cracking resistance due to rubber modification. The improvement of high- or low-temperature performance is more prominent at higher rubber concentrations. The effects of warm-mix additives on the rutting and thermal cracking performance are different. Generally, the wax-based additive improves the rutting resistance but negatively affects the low-temperature performance. In contrast, the chemical-based additive has an opposite effect except for the high-temperature performance of neat bitumen. The stiffening of the bitumen phase and the contribution of swollen rubber particles in the bitumen matrix together contribute to the peculiar viscoelastic response of CRMB, i.e., stiffer/softer and more elastic at high/low temperatures. This modification mechanism explains the superior rutting and thermal cracking performance of CRMB.

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Considering the application scenarios of rubber granules from waste tires in the bitumen modification process (wet or dry process), both aerobic and anaerobic aging of rubber may occur. The current study aims to investigate the thermal aging behavior of waste tire rubber samples using nanoindentation and environment scanning electron microscopy (ESEM) tests. Both aerobic and anaerobic aging tests with different durations were conducted on rubber samples. The complex moduli of aged rubber samples were measured by nanoindentation tests. The surface morphology and elemental composition of aged samples were obtained by ESEM tests together with the energy dispersive X-ray analysis. Results have shown that for both aerobic and anaerobic aging, the equilibrium modulus derived from the complex modulus curve first increases and then decreases with aging time. However, the time needed for the aerobically aged sample to reach the maximum equilibrium modulus is shorter than the anaerobic case. Aging results in crack propagation and an increase of sulfur content on the rubber surface until it reaches the peak. The degree of crosslinking reflected by sulfur content for anaerobic aging is higher than aerobic aging. The morphological change and elemental change of rubber correlate well with the change of mechanical properties. The aging of rubber from the waste truck tire at 180°C can generally be separated into two stages: crosslinking dominant stage and chain scission dominant stage.@en

Micromechanics, which can be used to relate the properties of a composite to the properties of individual constituents, is considered a good approach to understanding the fundamental mechanisms behind the behavior of asphalt materials. Compared with the semi-empirical and numerical micromechanical models, analytical micromechanical models do not need calibration factors. In addition, they can provide analytical solutions on the basis of a series of assumptions. Using these models, researchers have separated the effects of different stiffening mechanisms (i.e., the volume-filling reinforcement, the physicochemical reinforcement, and the particle-contact reinforcement) for mastic. However, similar research work has not been conducted for asphalt mixtures and, moreover, the characteristics of the particle-contact reinforcement have not been deeply analyzed by researchers. Therefore, this paper aims to understand the stiffness of asphalt mixture through micromechanics. The focus of this study was on porous asphalt mixture where particle-contact reinforcement plays an important role in its behavior. The stiffening effects of different mechanisms were separated using analytical micromechanical models. The effects of temperature/frequency and the properties of the matrix phase on the stiffening effect of the particle-contact reinforcement were analyzed.@en

Asphalt mixtures with high porosities (known as porous asphalt (PA) mixes) are becoming a popular choice among road authorities as it provides better skid resistance while also reducing tire-pavement noises. Towards the design and manufacture of PA mix pavement, the evaluation of the mechanical properties of PA mixes is of great importance. To predict the mechanical properties of PA mixes, micromechanical models have been considered as an effective tool. In most research studies, continuum-based micromechanical models, i.e. the Self-consistent model, the Mori-Tanaka model, etc. are widely used to predict the stiffness of asphalt mixtures. However, the limitation of these models is that they cannot describe the characteristics of individual particles and thus they cannot provide accurate predictions. On the other hand, the discrete-based micromechanical model (DBMM) which simulates a granular material as an assembly of bonded particles seems to be a promising alternative. Limited research studies have focused on studying the utilization and the applicability of this model for asphalt mixes. Therefore, this paper aims to propose a framework to use DBMM and to evaluate its performance in estimating a PA mix's stiffness. Based on the obtained results, both the merits and limitations of this model were highlighted.

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The degradation of bituminous materials as a result of ageing has a significant effect on asphalt pavement performance. In this study, one porous asphalt (PA) section and one stone mastic asphalt (SMA) asphalt pavement section were designed and constructed in 2014 and exposed to the actual environmental condition. To study the change in the pavement’s mechanical properties, asphalt cores were collected from both test sections annually. The change in stiffness modulus was determined via cyclic indirect tensile tests. To investigate the ageing behavior across the pavement depth, the bitumen was extracted and recovered from 13 mm slices along the depths of the cores. The chemical composition and rheological properties of the field-recovered bitumen, and that of original bitumen aged in standard short-and long-term ageing protocols, were investigated by means of the Fourier Transform Infrared (FTIR) spectrometer and Dynamic Shear Rheometer. The results show that the effect of mineral aggregate packing, and therefore of air-void distribution and connectivity, on the ageing sensitivity of the pavements with time was significant, as the changes in the stiffness of the PA mixture were greater than that of SMA mixture. In addition, the results of field-recovered bitumen show that there is an ageing gradient inside the porous asphalt layer, however, the ageing of SMA mainly happens on the surface of the layer. Finally, the field-recovered and laboratory-aged bitumen results demonstrate a weak relation between field and standard laboratory ageing protocols.

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This research involving two binders, a neat 70/100 paving grade bitumen and an epoxy-diluted bitumen, evaluated the effect of hydrated lime and limestone filler on the oxidative age hardening of binders. A pressure aging vessel (PAV) unit was used to mimic long-term oxidative aging, and the rheological properties of binders containing fillers were measured using a dynamic shear rheometer. The active nature of hydrated lime with binders was further verified by conducting elongation-to-fracture tensile tests. Results indicate that the effect of the filler reactivity is much more pronounced in epoxy bitumen than in neat bitumen, with the pure limestone filler showing the highest stiffening effect. The epoxy bitumen containing limestone filler was also tougher, showing higher elongation-to-break than the mastics generated with hydrated lime. Even though the epoxy bitumen containing limestone was the strongest and toughest material, it exhibited higher susceptibility to fracture after 80 h in PAV than of the same binder with hydrated lime. This research verifies earlier studies that hydrated lime could improve the low-temperature properties, resulting in the reduction of the deleterious effects of oxidative age hardening in bituminous binders.@en

The paper aims to simulate the micromechanical behavior of asphalt mixtures during the compaction process using the Discrete Element Method (DEM). The interactions between the components of a Porous Asphalt (PA) mixture were represented using an Elastic Viscoelastic Contact Model (EVCM), which is a user-defined model implemented in EDEM software, developed based on linear elastic and Burger's viscoelastic constitutive equations. The macroscale parameters of asphalt mortar were characterized using the nonlinear regression analysis of master curves obtained from Dynamic Shear Rheometer (DSR) tests. The verification process of EVCM successfully indicated that the computations trends fall within the range of expected values for the typical asphalt mixture material. Further, a Superpave Gyratory Compaction (SGC) test was carried out and the obtained sample was scanned using X-ray Computed Tomography (X-ray CT) to capture the air void distributions. The DEM was utilized where digital samples were established to simulate the overall process of laboratory and field compaction. The simulation results showed that the model provided a comparable prediction of responses and demonstrated the capability of SGC to fabricate a representative sample. The influence of temperature on the asphalt compaction process was explored and the results implied that temperature decreasing adversely affects the compactability and dramatically increases the demanded compaction efforts which are consistent with the law of viscoelasticity. On the contrary, when the temperature is high, the asphalt binder becomes too fluid and roller loads will simply displace, or “shove” the mat rather than compact it. Tracking the change in the air voids proportion indicates that the motion of aggregates is rather compound. The aggregates flowed vertically downwards in line with the compacting orientation while moved horizontally outwards away from the center. The results demonstrated that the model effectively simulated the compaction process, the developed model, and can be considered as a useful tool. All in all, the findings confirm that the concept is technically practicable, affording the model a tremendous potential to help researchers understand the microstructural phases of asphalt mixture during the compaction.

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Crumb rubber modified bitumen (CRMB) can be regarded as a binary composite system in which swollen rubber particles are embedded in the bitumen matrix. The current study aims to further improve the prediction accuracy of micromechanical models for CRMB by considering the interparticle interactions. To accomplish this goal, two different strategies were used. Firstly, the (n+1)-phase model was applied to the CRMB system by considering the multilayer properties of swollen rubber particles. Secondly, a new micromechanical scheme called the J-C model was used to account for the interparticle interaction issue. Results show that the (n+1)-phase models slightly increase the prediction accuracy but the underestimation of complex modulus at lower frequencies remains unsolved. The J-C model remedies the underestimation of modulus in the low-frequency range by other models and provides an overall improvement for the relative prediction accuracy by properly addressing the interparticle interactions from the perspective of particle configuration.

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The rejuvenation of epoxy modified bituminous binders is a topic of much debate because such binders may not be able to melt at high temperatures and restore their properties using recycling agents. This paper presents the results of an experimental program developed to evaluate the re-usability of an epoxy modified bitumen, or epoxy bitumen, by using three recycling agents: an aromatic-based agent, an aliphatic-based agent, and a soft binder. The impact of these agents on the response of aged binders was assessed by performing analyses in a Fourier Transformed Infrared spectroscopy and a Dynamic Shear Rheometer. Results indicated that diluting the epoxy binder with a base bitumen can be a feasible method for producing aging resistant binders of long curing time lengths. The most severely oxidized samples were blended with the recycling agents, and the aromatic agent has been proved as the most effective to recover the rheology of aged binders. Significant potential to recover the relaxation characteristics of epoxy bitumen has been demonstrated by using the soft binder. As a result, the epoxy bitumen has shown a similar ‘rejuvenation’ attribute with that of a conventional bitumen, and thus, it might be re-utilized through the standard asphalt recycling processes.@en