A Federal Highway Administration (FHWA) funded study was conducted to investigate the influence of extraction methods on aggregate properties. The properties of the virgin aggregates were compared with those of aggregates extracted from laboratory-produced recycled asphalt pavement (RAP) from four different aggregate sources. The extracted and actual asphalt binder contents were also compared. The study investigated the influence of the extraction method on tendencies to under- or over-estimated certain mix design properties. The test results were also examined to determine the impact of the RAP aggregate properties on the voids in mineral aggregate (VMA) over different RAP percentages. Recommendations were made for the most appropriate method to estimate the RAP aggregate specific gravities based on acceptable levels of error in VMA for mixtures with varying levels of RAP.
The main focus of this study was to obtain plant produced Reclaimed Asphalt Pavement (RAP) mixtures, to document the mixture production parameters and to evaluate the degree of blending between the virgin and RAP binders. The effect of mixture production parameters on the performance (in terms of stiffness, cracking, rutting, and moisture susceptibility) and workability of the mixtures was evaluated. Eighteen plant produced mixtures were obtained from three locations in the Northeast United States. RAP contents (zero to 40%) were varied and softer binders were used. The data and analysis illustrated that the degree of blending between RAP and virgin binders is a function of production parameters. The stiffness of the mixtures increased as the percentage of RAP increased, but not when the discharge temperatures of the mixtures were inconsistent. The cracking resistance was reduced as the percentage of RAP increased. The rutting and moisture damage resistance improved as the percentage of RAP in the mixtures increased. Finally, reheating the mixtures in the laboratory caused a significant increase in the stiffness of the mixtures.
This paper presents the results of a study to evaluate the mixture properties of plant-produced asphalt mixtures containing up to 40% reclaimed asphalt pavement (RAP). Five sets of asphalt mixtures were tested to determine their dynamic moduli and low temperature tensile creep compliance and strength. The mixture moduli were analyzed to assess changes in mixture behavior over a range of temperatures (frequencies) and in combination with extracted binder properties to analyze the extent of binder blending in the mix. The low temperature test results were analyzed to predict the critical cracking temperature of the mixtures. The results suggest that, for these materials, up to 25% RAP could be added to the mix with no change in the virgin binder grade without detriment to the low temperature properties of the mix.
The effect of reduced gyration levels on mix design and performance was quantified in this study. Changes in fatigue resistance and rutting resistance when design gyrations were decreased using different approaches were captured in laboratory tests. Using four separate mixtures, a standard 75 gyration design, a reduced 65 gyration design meeting standard volumetrics using additional binder, and a reduced 65 gyration design where standard volumetrics were met by adjusting the fine aggregate gradation rather than through the addition of binder, three various were studied. Using a suite of laboratory tests, the properties of the various mix designs were evaluated. Laboratory tests included the following: fatigue resistance, rutting resistance, and dynamic modulus. Using the shear response measured during gyratory compaction, compactability was assessed. Reducing gyrations and adjusting the fine aggregate gradation increased the average modulus, as shown in laboratory tests, and the average modulus decreased at lower gyrations when binder was increased. The same trend as dynamic modulus where adjusted fine aggregate gradations increased average resistance to permanent deformation was yielded by flow number tests, and added binder decreased average resistance to permanent deformation relative to the standard, reference mix design. Nonetheless, the inherent variability of the lab tests could not be overcome by the trends in the average modulus and permanent deformation responses, and the differences were largely insignificant. Both types of reduced design gyrations improved the compactability relative to the reference mix with higher design gyration, as indicated by the Compaction Force Index computed from the gyratory shear resistance. It is implied by this study that lowering design gyrations by a moderate level can, but not always, be used to achieve more compactable and more crack resistant mixtures without jeopardizing rutting resistance in a significant way. However, it is crucial to note that performance tests need to be completed due to the fact that a general or consistent rule does not apply. The reduced gyration level negatively affected some mixtures in the study. Due to the particulars of local materials, laboratory performance tests which can be conducted with an Asphalt Mixture Performance Tester are recommended for guidance.
This study was mainly focused on identifying appropriate relationships between asphalt mixture component characteristics and asphalt mixture properties known to control cracking performance. The current lack of material property models that can accurately describe the changes in material properties over time in the field is probably the greatest deficiency in our ability to accurately predict pavement performance. Therefore, there is a need to evaluate existing material property models, and develop improved models for use in the prediction of pavement performance. Relationships able to predict initial fracture energy and creep rate, which are the properties known to govern the change in material property over time and are also required for performance model predictions, were developed in this study. In addition, conceptual relationships were identified to describe changes in these properties over time (aging) by including the effect of the non-healable permanent damage related to load and moisture. This can serve as the foundation for further development of improved models to predict mixture properties as a function of age in the field based on additional field data and laboratory studies using more advanced laboratory conditioning procedures. The verified relationships will also serve to provide reliable inputs for prediction of service life using pavement performance prediction models.
The semi-circular bend (SCB) test configuration has been favored by many researchers due to the ease of sample preparation, including cores removed from the field and the quick and simple testing procedure. It offers the potential of assessing the cracking resistance of asphalt mixes in the laboratory in the design phase as well as in QA (quality assurance) testing activities. The objective of this study was to conduct a comprehensive evaluation of the SCB test and to utilize this test to evaluate a number of asphalt mixtures against cracking failure. Results of the experimental program were used to validate a three-dimensional (3D) finite element (FE) model, which was used to interpret and to analyze the failure mechanisms in the SCB test. Results of the experimental program showed that the SCB test results successfully predicted the fracture performance of the evaluated mixes and was able to differentiate between them in terms of cracking resistance. Mixtures prepared with polymer-modified binders were the best performers in this test against fracture. Results of the SCB test were in agreement with the DCSE (Dissipated Creep Strain Energy) test and identified the mixtures with high recycled asphalt pavement (RAP) content and the one prepared with unmodified binder as possible poor cracking performers in the field. The SCB test process as well as the propagation of damage were successfully simulated using 3D FE and cohesive elements. The presented modeling approach was in good agreement with measured test results for all mixtures. Based on the results of the FE model, damage that propagates in the vicinity of the notch is mainly caused by a combination of vertical and horizontal stresses in the specimen. The effect of shear was negligible in progressing damage in the specimen.
This paper presents a unique approach to analyzing surface cracking in hot mix asphalt (HMA) pavements, based upon the concept of reduced cycles. In the first half of the paper, empirical equations are presented for predicting damage curves for any HMA mixture under a wide range of loading conditions. These equations have been developed using a large database of fatigue test results, and confirmed with data from several independently gathered data sets. The equations use as predictors modulus and other parameters calculated from the change in modulus with time and/or temperature. The second half of the paper applies these equations to fatigue experiments carried out at the Federal Highway Administrations Automated Loading Facility (ALF) in McLean, VA. This analysis involved estimating the reduced cycles at critical points in the surface of the test sections at the initial appearance of surface cracking. Statistical methods were then used to develop equations for predicting the onset of cracking. Although the approach is promising, some additional work is needed before the method should be applied to general problems in pavement design and analysis.
The Semi-Circular Bending (SCB) fracture test is commonly used to evaluate the low temperature fracture properties of asphalt mixtures. The present work investigates the presence of a size effect in SCB fracture testing of asphalt mixtures. Un-notched and notched geometrically similar SCB specimens of various sizes are tested at -24°C loaded by crack-mouth opening displacement (CMOD). The effect of specimen size on the nominal strength is investigated through the well-established size effect theories and conclusions are drawn regarding the fracture behaviour of mixtures at low temperature.
The behavior of the interface between adjacent pavement layers is one of the most important factors affecting pavement performance. Despite the importance of interface behavior between different pavement layers, there are few guidelines that can be used for construction, and the selection of tack coat type, application rate, and placement is usually based on empirical judgment. This paper presents a new fracture-energy based Interface Bond Test (IBT), which can be a practical method to evaluate the bond between pavement layers. The results of laboratory and field studies demonstrate the ability of the test to distinguish between samples produced with different tack coat application rates and modified versus unmodified tack coat material. Results from the IBT test were also compared with direct tension tests, and similar trends were found to exist.
Top-down cracking is a distress mode that is of particular concern for pavements with Open-Graded Friction Course (OGFC) because open-graded mixture has considerably lower resistance to fracture (lower fracture energy limit and lower resistance to damage) than dense-graded mixture. This particular cracking phenomenon initiates on the pavement surface and propagates downward; so because the OGFC layer is thin, cracking performance relies on the properties and characteristics of three components near the pavement surface: OGFC, underlying structural layer, and the interface between. For this reason, to increase the durability of pavements surfaced with OGFC, it is significant to ensure a quality fracture resistant bond between OGFC and the structural layer. This research investigated top-down cracking performance of OGFC with different tack coats using a newly developed composite specimen interface cracking (CSIC) test. In addition, X-ray computed tomography (CT) was employed to analyze the interface characteristics between OGFC and dense-graded HMA. HMA fracture mechanics was employed to quantify the effect of polymer modified asphalt emulsion (PMAE) on pavement top-down cracking resistance enhancement. Results clearly indicated that PMAE-created bonded interface conditions greatly increased pavement top-down cracking resistance as compared with conventional tack coat.
The performance of asphalt mixture is governed by its viscoelastic properties, especially those in tension mode. However, due to the difficulties in performing tests in direct tension mode, the test methods commonly used are in either compression or indirect tension (diametrical compression) mode. Previous studies show that loading mode has a significant effect on the viscoelastic properties of asphalt mixtures, especially at high temperatures. It is of great importance to develop a testing method to effectively and efficiently characterize the tensile properties of asphalt mixtures. In this study, a flexural tension test was proposed to utilize a loaded wheel tester (LWT) to characterize the viscoelastic properties of asphalt mixtures. In this test, beam specimens were subjected to constant or cyclic loads provided by moving wheels of a LWT. With transducers mounted on the beam, flexural bend deformations are measured. In addition to the LWT test, uniaxial tests in tension mode, tension-compression mode, and compression mode as well as indirect tension creep test were conducted on the same asphalt mixtures for comparison and validation. The results showed that the LWT test was able to characterize the viscoelastic properties of asphalt mixtures made with different aggregates and asphalt binders. The results from the LWT tests were found to be in general accordance with those from other tests. Compared to uniaxial and indirect tension tests, the LWT test could better represent the stress state in pavements and thus was more suitable for characterizing the viscoelastic properties of asphalt mixtures.
Characterization of the asphalt concrete microstructure using two-dimensional (2-D) imaging techniques is an economically efficient approach. However, the features that have been captured and quantified using 2-D imaging in most published research have been limited to simplistic analyses of aggregate structure. The present research focused on introducing a more elaborate method of characterization of internal structure, and proposing new indices to relate to and explain rutting resistance performance of asphalt mixtures. The aggregate internal structure provides the skeleton of the asphalt concrete, which plays an important role in rutting resistance. It is shown that this structure can be captured using a combination of image analysis indices developed in this research, namely: number of aggregate-on-aggregate contact points, contact length/area, and contact plane orientation. These parameters are defined for both the total aggregates and for the effective load bearing aggregate structure, referred to as the 'skeleton' in this study. Software developed in a previous study and significantly modified for this paper, is used to process digital images of a set of asphalt mixtures with different gradations, binder contents, types of modification, and compaction efforts. The results demonstrate a correlation between the internal structure indices and the mixture rutting performance. Additionally, the indices were successfully used to capture the effect of compaction effort, gradation quality, and binder modification on the mixture internal structure.
Within the construction community, efforts to conserve energy and reduce emissions in asphalt paving applications have led to an increase in the usage and popularity of sustainable pavement design practices. Cold mix asphalt (CMA) is one such practice, as it consumes less energy in key components of the mix production process by allowing materials to be produced and mixed at ambient temperatures, thus allowing pavers to reduce total energy usage and emissions. CMA remains a limited niche material in most areas of the United States, despite its apparent energy and emissions benefits, because of lack of knowledge in CMA mix design, comparatively high emulsified asphalt costs, and, most importantly, unknown criteria for volumetric and performance characteristics of the constructed CMA pavement. A review of the current CMA mix design procedures and challenges associated with their usage is presented in this paper, and insight into the initial phases of developing a more comprehensive laboratory mix design method is offered. Aggregate coating and the determination of appropriate compaction conditions for dense graded CMA samples using a modified Superpave Gyratory Compactor (SGC) are the focus for the laboratory testing in this study. Using imaging analysis software, which provides a more objective and reliable method than visual observations, aggregate coating was evaluated. Aggregate coating is dependent on the selected emulsion content, laboratory mixing time and mixing condition, aggregate gradation, and to a lesser extent, pre-mix aggregate moisture, as indicated by the results. A high dependence on compaction pressure and sample curing time is suggested by volumetric analyses of compacted samples.
The objectives of this study were to perform a rutting characterization of warm mix asphalt (WMA) mixtures and mixtures containing high reclaimed asphalt pavement (RAP) and to determine the effects of production temperature and material type on permanent deformation. This study was based on data from the National Center for Asphalt Technology (NCAT) Test Track Phase IV research cycle and included a control section, two WMA sections and two sections with 50% RAP. Field measurements indicated that high RAP mixes had higher moduli and experienced lower vertical pressures than virgin mixes. The use of WMA technologies tended to increase permanent deformation while the addition of high RAP contents resulted in less rutting. Laboratory tests on recovered binders showed increased binder stiffness for high RAP mixes and no significant effect for virgin WMA mixes. Mixture tests of laboratory compacted samples did not reflect the observed field performance accurately.
An area of rapid growth, particularly in the United States and Europe, is the production of renewable liquid transportation fuels. The potential for using co-products from this rapidly growing manufacturing base as blending components in asphalt is examined in this paper. Preparations of several blends of biofuel co-products in a paving grade asphalt binder were made, and measurements of performance grading properties were taken. In accordance with American Association of State Highway and Transportation Officials (AASHTO) T283 to evaluate resistance to moisture damage, asphalt concrete mixtures using the various blends and a somewhat moisture sensitive aggregate were tested. Some of these materials may be useful as binder extenders, having minimal impact on the performance grade while imparting added benefits, as indicated by initial laboratory findings.
With the ability to trap and decompose organic and inorganic air pollutants, titanium dioxide (TiO2) is a promising technology to mitigate the harmful effects of vehicle emissions as a pavement coating. By introducing a new class of mixtures with superior environmental performance, this technology may revolutionize construction and production practices of hot-mix asphalt. Assessing the benefits of incorporating TiO2 in asphalt pavements was the objective of this study. The photocatalytic effectiveness and durability of a water-based spray coating of TiO2 was evaluated in the laboratory, in order to achieve this objective. Also presented in this study is the field performance of the country's first air-purifying photocatalytic asphalt pavement, located on the campus of Louisiana State University (LSU). It was shown by laboratory evaluation that TiO2 was effective in removing nitrogen oxide (NOx) and sulfur dioxide (SO2) pollutants from the air stream with an efficiency ranging from 31 to 55% for NOx pollutants and 4 to 20% for SO2 pollutants. Removal efficiency was achieved at a maximum for NOx and SO2 removal at an application rate of 0.05 l/m². The efficiency of NOx reduction is additionally affected by the flow rate of the ultraviolet (UV) light intensity, pollutant, and relative humidity. It is shown by preliminary field measurements that the measured NO concentrations were significantly reduced right after the application of the TiO2 surface coating on the asphalt pavement. However, in order to determine the durability of the surface coating, further field evaluation is required.
This publication comprises papers presented at the annual meeting of the Association of Asphalt Paving Technologists that focus on all phases of asphalt research and applications, including mixing, mixture elements, and testing.Two highlights of this series volume are solutions to production and scale-up problems in asphalt plants, and an entire section is devoted to asphalt research and applications in Latin America. Technical sessions include the following topics: sustainable photocatalytic asphalt pavements; renewable fuel co-products; rutting characteristics of warm mix asphalt (WMA) and high reclaimed asphalt pavement (RAP) mixtures; laboratory and coating compaction procedures for cold mix asphalt; internal structure characterization of asphalt mixtures; viscoelastic properties of asphalt mixtures; interface condition characteristics and open-graded friction course; fracture energy; fatigue damage modeling; cracking resistance; asphalt mixtures with dry added ground tire rubber; loose mix aging and warm mix asphalt; grave bitumen 5 (GB5) mix design; high polymer plant-produced mixtures; bond energy; physico-chemical interaction; aging procedures; and delayed mechanical response in modified asphalt binders. Papers from the Symposium include the following topics: recent advances in production facilities; production and construction of hot mix asphalt (HMA) and WMA; layer thickness and achieving density; best practices for HMA longitudinal joints; and milling and paving operations. Papers from the International Forum include the following topics: asphalt specifications in Latin America; asphalt technology in Chile; asphalt specifications in Colombia; and asphalt research and specifications in Central America-Costa Rica.
Bien que les lignes d’alerte audiotactiles aient fait leurs preuves en termes de réduction des accidents par sortie de voie, l’utilisation de ce dispositif de sécurité reste limitée, probablement à cause de l’absence de lignes directrices pratiques et de l’idée qu’elles s’accompagnent de problèmes tels que la pollution sonore, la gêne pour les deux-roues et une difficulté d’entretien. Ce dossier a comme objectif de décrire les différents dispositifs qu’il est possible d’installer, leurs caractéristiques géométriques et leur efficacité afin de synthétiser les paramètres pratiques principaux entrant en ligne de compte, et ainsi d’aider le gestionnaire dans sa décision de conception et de placement afin de maîtriser les inconvénients cités ci-avant, aux fins de réduire le nombre d’accidents par sortie de route. Ce document repose principalement sur une analyse approfondie de la littérature américaine (les bandes d’alerte sonores y étant abondamment utilisées) et des résultats du projet français Roadsense (chapitres 2 à 4). Le chapitre 5 propose, sous la forme d’une liste de questions, une aide à la décision pour guider les concepteurs et les gestionnaires dans le choix de recourir à l’usage des lignes d’alerte audiotactiles. Enfin, le chapitre 6 présente les conclusions de toute cette démarche, ainsi que les perspectives en termes d’études complémentaires, veille technologique et développement futur.
Pour les revêtements modulaires, le jointoiement constitue un élément essentiel de la structure de voirie. Pour pouvoir effectivement remplir le rôle de revêtement, les joints doivent toujours être remplis du matériau approprié. Le type de matériau de jointoiement et la durabilité du joint dans son ensemble sont donc aussi de grande importance pour la stabilité du revêtement à long terme. Cette publication CRR fait le compte rendu du projet biennal de recherche prénormative PREVOSTRAT (en entier “Prestatie-eisen voor innovatieve voegvullingsmaterialen in bestratingen met kleinschalige elementen”), réalisé par le CRR avec le soutien du SPF Economie et le Bureau de Normalisation (NBN) et en collaboration avec l’Universiteit Gent (unité d’enseignement Plantaardige Productie). L’étude avait pour but d’établir des méthodes d’essai et les exigences performantielles correspondantes pour des matériaux de jointoiement innovants, liés ou non, appliqués dans les revêtements routiers modulaires (en béton, terre cuite ou pierre naturelle). Parallèlement aux conclusions principales et résultats de l’étude, ce compte rendu de recherche propose également des directives et des recommandations pour des exigences relatives aux matériaux de jointoiement dans les normes européennes et/ou cahiers des charges types belges.
ln the coming years, it is anticipated that the current Canadian climate will no longer be the norm, and temperatures will steadily increase as a result of anthropogenic climate change. Increased greenhouse gas concentrations in the atmosphere are the root cause of changing climate, which is only expected to worsen over time. Pavement performance models show that changing climate will result in accelerated pavement deterioration. To mitigate pavement deterioration, various adaptation strategies have been suggested in the recent literature. One of these adaptation strategies is upgrading the Superpave™ asphalt binder grade. It is well known that asphalt binder is highly sensitive to climate factors such as temperature and percent sunshine. Hence, reviewing asphalt binder grade is a vital step, and that can help decelerate pavement deterioration. This study aims to understand the impact of climate change on existing flexible pavements and identify the appropriate binder grades necessary to accommodate these effects across Canada. To achieve this goal, the analysis was carried out in six phases. Comparing pavement performance between current binder grades and proposed future binder grades confirms the necessity of considering proposed asphalt binder grades for future climate.