1,720,993 research outputs found
A framework for characterizing RAP clustering in asphalt concrete mixtures
No full textRecycled Asphalt Pavement (RAP) is commonly used in asphalt for road rehabilitation or new constructions. Nevertheless, some physical and chemical phenomena that occur during production, laying and compaction of mixtures containing RAP are not yet completely explored. One of the main aspects is represented by the interaction between the aged bitumen from RAP and the virgin bitumen added to the mixture as well as the creation of clusters among small-size RAP particles. In this paper several combinations of mixtures are studied, varying the amount of RAP, the type of new binder and the testing temperature in order to obtain a suitable data set for the development of a framework for characterizing clustering of RAP during mixing hot recycled asphalt concrete based on the parameters mentioned above. For analyzing the experiments, the Response Surface Methodology (RSM) was applied. The set of points (combinations tested) for calibration of the models was selected using the Dohelert network, which is a design optimization strategy that allows the effective estimation of the models coefficients. The agglomeration of RAP particles is investigated for all virgin binders used and for all the percentages of RAP. It was shown that the quantity and the quality of virgin aggregates play a significant role in the clusters formation. Moreover, this experimental work suggested that revised formula for the calculation of the bitumen film thickness is needed, in order to include the combined effect of bitumen penetration and fabrication temperature. (C) 2015 Elsevier Ltd. All rights reserved.LAVO
Characterization of Water Sensitivity of Asphalt Mixtures with Coaxial Shear Test
No full textThe CoAxial Shear Test (CAST) performs fatigue test under simultaneous action of dynamic loading, temperature cycles and water, and modulus test on wet or dry specimen. Both a dense graded and an open graded mixture were studied at different air void content. The water sensitivity of both mixtures was determined by comparing fatigue performance of dry and wet tests. Additionally, the effects of water action, temperature and loading cycles were also investigated by comparison of modulus test before (undamaged specimen) and after (damaged specimen) each fatigue test. The introduced Water Sensitivity Index for fatigue test confirms that water damage in asphalt pavements is considerably related to air voids. Finally, the modulus test analysis allowed explaining also the different consequences of environmental factors on viscoelastic properties of asphalt mixtures by using the Standard Linear Solid model. © 2008 Lavoisier.The CoAxial Shear Test (CAST) performs fatigue test under simultaneous action of dynamic loading, temperature cycles and water, and modulus test on wet or dry specimen.
Both a dense graded and an open graded mixture were studied at different air void content. The water sensitivity of both mixtures was determined by comparing fatigue performance of dry and wet tests. Additionally, the effects of water action, temperature and loading cycles were also investigated by comparison of modulus test before (undamaged specimen) and after (damaged specimen) each fatigue test.
The introduced Water Sensitivity Index for fatigue test confirms that water damage in asphalt pavements is considerably related to air voids. Finally, the modulus test analysis allowed explaining also the different consequences of environmental factors on viscoelastic properties of asphalt mixtures by using the Standard Linear Solid model
Damage model for environmental conditioned fatigue test with CAST
No full textThe aim of this paper is to suggest a unified test method that allows investigation into
the different effects and contribution of water damage and temperature cycles on fatigue
performance of asphalt mixtures by means of a CoAxial Shear Test (CAST). A continuum
damage approach, based on the elasticity theory, is chosen to determine the damage level
of each tested specimen. The proposed mathematical model allows the simulation of the
modulus evolution in the fatigue test and takes into account the temperature cycles. In
this way, a unique scalar damage factor determines the damage process severity in each
specimen and allows a rational comparison between each different condition
Influence of water and temperature on mechanical properties of selected asphalt pavements
No full textOne of the main causes of distress in asphalt pavements is water damage. The purpose of this paper is to compare different test methods to evaluate moisture susceptibility. This is of special importance because of the insufficient effectiveness of the procedures currently used. In this research experiments were conducted to investigate the effects of water and temperature on mechanical properties of mixtures with different air voids content. The evaluation of such properties concentrates on the following three approaches: innovative (Coaxial Shear Test), traditional (Indirect Tensile Test) and empirical (Cantabro Test). Specimens were prepared by means of Superpave Gyratory Compactor (SGC) and divided in two different subset for controlled dry and wet conditioned testing. Test results indicated that Indirect Tensile Test (IDT) is not able to discriminate between wet and dry condition as the Coaxial Shear Test (CAST) does. The CAST method reproduces closest the real field conditions and indicates clearly the risk of water damage for open graded mixtures (high air voids content). Dense graded mixtures (low air voids content) showed less influence probably due to the reduced amount of penetrating water. Cantabro Tests (CAT) provided also significant results in good correlation with air voids content and material properties of asphalt mixes
Influence of water and temperature on mechanical properties of selected asphalt pavements
No full textLes dégâts causés par l’eau sont une des causes les plus importantes de la dégradation des chaussées. Cet article présente une comparaison de différentes méthodes d’essai utilisées pour évaluer la susceptibilité à l’eau des enrobés bitumineux.
Les effets de l’eau et de la température sur les propriétés mécaniques d’enrobés présentant des teneurs en vides différentes ont été étudiés. L’évaluation de ces propriétés repose sur les trois approches suivantes: innovatrice (essai de cisaillement coaxial), traditionnelle (essai de traction indirecte) et empirique (essai Cantabro). Les éprouvettes ont été confectionnées à l’aide d’un compacteur giratoire superpave et réparties en deux sous-ensembles pour les essais en conditions sèches et en conditions humides.
L’évaluation des résultats montre que l’essai de traction indirecte ne permet pas de différenciation entre les résultats obtenus à l’état sec et l’état humide alors que l’essai de cisaillement coaxial permet de mettre clairement en évidence les dommages causés par l’eau sur les enrobés à haute teneur en vides. Les enrobés à teneur en vides peu élevée présentaient des dommages moins importants ce qui est probablement dû au fait que la quantité d’eau pouvant pénétrer dans les éprouvettes est faible. L’essai de cisaillement coaxial reproduit ainsi très fidèlement les conditions in situ.
L’essai Cantabro fournit lui aussi des résultats significatifs qui sont en étroite corrélation avec la teneur en vide et les propriétés mécaniques des enrobés.One of the main causes of distress in asphalt pavements is water damage. The purpose of this paper is to compare different test methods to evaluate moisture susceptibility. This is of special importance because of the insufficient effectiveness of the test procedures currently used.
In this research, experiments were conducted to investigate the effects of water and temperature on mechanical properties of mixtures with different air void content. The evaluation of such properties concentrates on the following three approaches: innovative (Coaxial Shear Test), traditional (Indirect Tensile Test) and empirical (Cantabro Test). Specimens were prepared by means of Superpave Gyratory Compactor (SGC) and divided in two different subsets for controlled dry and wet conditioned testing.
Test results indicated that the Indirect Tensile Test (IDT) is not able to discriminate between wet and dry condition as the Coaxial Shear Test (CAST) does. The CAST method reproduces closest the real field conditions and indicates clearly the risk of water damage for open graded mixtures (high air void content). Dense graded mixtures (low air void content) showed less influence probably due to the reduced amount of penetrating water.
Cantabro Tests (CAT) provided also significant results in good correlation with air void content and material properties of asphalt mixes
An advanced methodology for the mix design optimization of hot mix asphalt
No full textThe bitumen quantity to add to asphalt mixtures depends on the surfaces of aggregates and filler to be coated. The formulas currently available in the literature have limitations such as considering all the fillers with the same specific surface or the aggregates with spherical or cubical shapes. This paper aims to define an analytical approach for the determination of the optimal dosage of bitumen in HMA proposing new methodologies to go a step further in the resolution of the above mentioned approximations. Indeed, new surface area factors were calculated to determine the aggregates surface considering their real shapes and volumes. Afterwards, the authors proposed a detailed characterization of two types of fillers and the critical filler concentration, introduced by Faheem and Bahia, was used to calculate the minimum amount of bitumen for maintaining the mastic in a diluted state and filling the voids in the mixtures. Finally, a verification of the formula developed was carried out with specific laboratory tests. These results allow the challenge of revising the method of calculating the specific surface of the aggregates and filler to be addressed with the final goal to include them in a new mix design optimization for HMA. (C) 2016 Elsevier Ltd. All rights reserved.LAVO
Repeatability of Interlayer Shear Resistance determined With Two Test Procedure
Full text linkInterlayer bonding significantly influences the performance of multi-layered pavement systems. To correctly know how this bonding modifies the interlayer mechanical performance, theoretical and experimental projects are currently in progress in many countries. However, different equipments generally provide different results because these results are obtained under different test conditions in terms of applied stress and strain, rate of displacement, specimen size and specimen confinement. Since in European Standards there is a normative gap regarding interlayer resistance tests, in Italy a draft of a standard is currently under development based on a laboratory direct shear device called ASTRA (Ancona Shear Testing Research and Analysis). In the present paper, the repeatability of ASTRA test method is studied by analyzing the results obtained in two experimental investigations. In the first investigation, specimens prepared with the same material and the same compactor were tested with ASTRA test method and with another shear test method, the LPDS (Layer-Parallel Direct Shear), which is compatible with Swiss Standards (Schweizer Norm SN 671961, 2000). In the second investigation, the first series of ASTRA results were compared with repeatability results obtained by using different materials and different compaction methods for the double-layered specimens. The study shows that the two shear test equipments provide the same precision level in terms of scatter of the results. Moreover, the ASTRA investigation shows that the repeatability depends not only on the test method but also on the pavement material and compaction method. This study allows supporting Italian standardization of interlayer shear resistance testing and, at the same time, it shows that it is necessary to further investigate different materials and different compaction methods to improve the knowledge on repeatability
Influence of contact surface roughness on interlayer shear resistance
Full text linkRegarding performance of multi-layered asphalt pavement systems, interlayer bonding has an important role because it considerably influences stress and strain distribution in the pavement. Interlayer shear resistance may depend on various factors such as type and presence of tack-coat, maximum aggregate size and air void content of the two mixes in contact, as well as roughness conditions at the interface. This study, which is part of an ongoing research project, focuses primarily on the possible relationship between interlayer shear resistance and lower layer surface roughness of double-layered asphalt concrete specimens. In addition, the study deals with the comparison of different methods to evaluate this contact surface roughness. Before placing the upper layer, two different methods were applied to determine surface profiles: a laser profilometer and a profile comb. The obtained profiles were used to perform MPD (Mean Profile Depth) and fractal dimension evaluations. Moreover, the lower layer surface roughness was evaluated with the traditional sand patch method. Each technique was used to seek a relationship between the contact surface roughness and the interlayer shear resistance measured by both ASTRA (Ancona Shear Testing Research and Analysis) test device and LPDS (Layer-Parallel Direct Shear) test device. The results show that greater contact surface roughness leads to an increase in ASTRA and LPDS interlayer shear resistance in different proportions for MPD, fractal dimension and sand patch method roughness evaluation
Characterization of Water Sensitivity of Asphalt Mixtures with Coaxial Shear Test
No full textThe CoAxial Shear Test (CAST) performs fatigue test under simultaneous action of dynamic loading, temperature cycles and water, and modulus test on wet or dry specimen. Both a dense graded and an open graded mixture were studied at different air void content. The water sensitivity of both mixtures was determined by comparing fatigue performance of dry and wet tests. Additionally, the effects of water action, temperature and loading cycles were also investigated by comparison of modulus test before (undamaged specimen) and after (damaged specimen) each fatigue test. The introduced Water Sensitivity Index for fatigue test confirms that water damage in asphalt pavements is considerably related to air voids. Finally, the modulus test analysis allowed explaining also the different consequences of environmental factors on viscoelastic properties of asphalt mixtures by using the Standard Linear Solid model. © 2008 Lavoisier
Analysis of water and thermal sensitivity of open graded asphalt rubber mixtures
No full textThis research investigates the water and thermal sensitivity of two open graded mixtures prepared with
asphalt rubber binder, one mixture containing lightweight aggregates (expanded clay) replacing a part of
coarse fraction. Fatigue tests using the CoAxial Shear Test (CAST) apparatus were performed in both dry
and wet conditions with and without temperature cycles. Results showed that fatigue resistance of the
studied materials was only little affected by water and temperature cycles and superior to traditional
open graded mixtures produced with SBS modified bitumen only. The results were also validated and
modelled by means of an elasticity-based damage model
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