Search

This paper presents the performance evaluation of unmodified and lime-modified hot mix asphalt (HMA) mixtures at varying asphalt content using asphalt mixture performance test developed from National Cooperative Highway Research Program project 9-19 and 9-29 and the viscoelastic continuum damage finite element analysis. Test methods adopted in this study are the dynamic modulus test for stiffness, the triaxial repeated load permanent deformation test for rutting, and the direct tension test for fatigue cracking. The findings from this study support conventional understanding of the effects of asphalt content and lime modification on the fatigue cracking and rutting performance. Finally, the optimum asphalt content for both lime-modified and unmodified mixtures are proposed based on the knowledge gleaned from the performance-based mix design methodology. With additional validation and calibration, the comprehensive methodology described in this paper may serve as the foundation for a performance-based HMA mix design and performance-related HMA specifications. [ABSTRACT FROM AUTHOR]

The benefits of using hydrated lime as an additive in asphalt concrete are well known. When added to asphalt concrete mixtures hydrated lime shows the beneficial effects of filler, while also improving resistance to moisture damage. Even with the great deal of literature and experience extolling the benefits of hydrated lime, little research exists regarding the impact of hydrated lime on the fundamental behavior and performance of asphalt concrete mixtures. This paper presents findings of the impact of lime introduction method on the volumetric optimums and the fundamental behavior and performance of asphalt concrete mixtures. The behavior of various mixtures is assessed with the dynamic modulus tests and through characterization tests for the viscoelastic continuum damage model, a mechanistically based material model. Permanent deformation performance assessment is made with triaxial repeated load permanent deformation tests. From the experimental investigation it is found that the method of lime introduction can have an important effect on the optimum volumetric asphalt content. Regarding mixture performance it is found that hydrated lime has a minimal impact on the dynamic modulus of the mixtures in this study. Conversely, it is found that hydrated lime has a positive effect on both the permanent deformation and fatigue cracking performance of asphalt concrete mixtures. The magnitude of this positive impact is shown to be affected by the method used to introduce hydrated lime into the mixture. [ABSTRACT FROM AUTHOR]

For the past few decades, the stiffness of asphalt material has been commonly characterized by means of resilient modulus. However, the resilient modulus is not a fundamental material property, and hence, the concept of resilient modulus has been subsequently diminished in the latest Mechanistic-Empirical Pavement Design Guide (MEPDG). Although the MEPDG could not endorse the resilient modulus as the primary means for asphalt concrete characterization, it has been a primary mixture test, and a considerable amount of laboratory testing has been conducted to date. In this paper, an analysis methodology for backcalculating the dynamic modulus from the resilient modulus test data is introduced. The strong advantage of such a methodology is that the existing resilient modulus data can be reused for estimating the dynamic modulus. The approach would significantly save time and effort in reevaluating the dynamic modulus of asphalt mixture for which the resilient modulus test data are available. [ABSTRACT FROM AUTHOR]

Passive energy dissipation devices, such as, viscous, viscoelastic, and friction devices are generally installed in buildings using diagonal or chevron braces. To increase the effective damping force and to reduce the damper volume, various magnifying system of the damper displacement, such as, toggle brace system and scissor-jack-damper configuration have been developed with increase in installation cost. In this study, new installation scheme for passive dampers was proposed using cables installed in such a way that relative displacement equal to storey displacement occurs between the cable and the structure when the structure is subjected to lateral load. The cables can be installed continuously or discretely between base and top storey of the structure. To verify the validity of the proposed method nonlinear dynamic analysis of model structures with viscoelastic dampers installed using the proposed configuration scheme was carried out using three earthquake records and two sinusoidal forces. According to the analysis, the proposed method resulted in significant reduction in the size of dampers compared with the conventional installation methods. Les dispositifs passifs de dissipation d'énergie, tels que les amortisseurs visqueux, viscoélastiques et à friction, sont généralement installés dans les bâtiments en utilisant des entretoises diagonales ou en chevron. Afin d'accroître la force efficace d'amortissement et de réduire le volume de l'amortisseur, divers systèmes d'amplification du déplacement de l'amortisseur, tels qu'un système d'amortisseurs pour contreventements à fixations grenouillères et des amortisseurs à vérin hydraulique ont été développés avec l'augmentation du coût d'installation. Dans cette étude, un nouveau plan d'installation des amortisseurs passifs est proposé qui utilise des câbles installés de manière à ce qu'un déplacement relatif égal au déplacement des étages survienne entre le câble et la structure lorsque cette structure est soumise à une charge latérale. Les câbles peuvent être installés en continu ou en discontinu entre la fondation et l'étage supérieur de la structure. Pour vérifier la validité de la méthode proposée, une analyse dynamique non linéaire des structures de modèles avec amortisseurs viscoélastiques installés en utilisant la configuration proposée a été réalisée en utilisant les registres de trois séismes et de deux forces sinusoïdales. Selon les résultats de l'analyse, la méthode proposée permet de réduire significativement la dimension des amortisseurs par rapport aux méthodes conventionnelles d'installation. [ABSTRACT FROM AUTHOR]

This paper presents the results of an exploratory analysis of falling weight deflectometer (FWD) data collected on a large project about the spring thaw behaviour of pavements. The test site includes four test sections, two of which are conventional flexible pavement structures, whereas the other two are built with a cement-treated base. The aim of this study is to verify the applicability of using FWD time history data to evaluate damage to a road during the thawing period. The applicability of the analysis techniques is verified through the phase angle and dissipated energy. The data analyzed were obtained from tests conducted with an FWD on one flexible pavement test section. The results obtained showed a clear difference between the winter, thawing, and summer periods. It was found that the phase angle and dissipated energy can be used to evaluate the road damage during the thawing period through quantification of the phase angle and dissipated energy. These factors can also be used to describe the pavement behaviour in terms of elasticity and viscoelasticity. Cet article présente les résultats d'une analyse exploratoire de données de déflectomètre à masse tombante (FWD) colligées lors d'un grand projet sur le comportement des chaussées lors du dégel du printemps. Le site d'essai comprend quatre sections : deux ont des structures conventionnelles de chaussée flexible et les deux autres sont construites sur une fondation traitée au ciment. L'objectif de l'étude est de vérifier l'applicabilité des données historiques FWD pour évaluer le dommage à la route durant la période de dégel. L'applicabilité des techniques d'analyse est vérifiée par l'angle de phase et l'énergie dissipée. Les données analysées ont été obtenues lors d'essais réalisés avec le déflectomètre à masse tombante sur une section d'essai de chaussé flexible. Les résultats montrent une différence évidente entre les périodes d'hiver, de dégel et d'été. Il s'est avéré que l'angle de phase et l'énergie dissipée peuvent être utilisés pour évaluer les dommages à la route durant la période de dégel en quantifiant l'angle de phase et l'énergie dissipée et en décrivant le comportement de la chaussée en termes d'élasticité et de viscoélasticité. [ABSTRACT FROM AUTHOR]

The relaxation modulus E(t), creep compliance D(t), and complex modulus E*(ω) are functions often used to characterize the linear viscoelastic (LVE) behavior of hot mix asphalt (HMA). Interconversions among these LVE functions are often required. To perform an interconversion, one of the key steps is to express both the source and target LVE functions in Prony series representations. To obtain the corresponding Prony series coefficients, the collocation method and linear least squares method were often used in the past. However, the problem encountered with these two methods is in manually assigning part of the Prony series coefficients; resulting in unrealistic or negative Prony coefficients and big discrepancies between the fitting data and the original data. To address this problem, this paper developed a new algorithm by incorporating the Levenberg-Marquardt method. This new algorithm has four unique features, it (1) allows all the Prony series coefficients to be freely adjustable, (2) guarantees all positive Prony series coefficients, (3) determines all Prony series coefficients automatically and simultaneously, and (4) ensures very accurate interconversion through the fact that the fitting curve almost completely coincides with the original curve. Furthermore, to facilitate the implementation of practical applications of this new algorithm, it was incorporated into a stand-alone, windows-based software named “LVEmaster”. The simplicity and accuracy of this new interconversion software was demonstrated through a series of interconversions among HMA LVE functions. [ABSTRACT FROM AUTHOR]

This paper describes the development and application of a computational modeling approach incorporated with pertinent laboratory testing that can be used to predict fracture damage performance of bituminous paving mixtures. In the model, material viscoelasticity, mixture microstructure, and cohesive zone fracture properties are implemented within a finite element method, which is intended to simulate nonlinear-inelastic microscale fracture and its propagation to complete failure in bituminous mixtures. The model is applied to different materials, and the resulting model simulations are compared to experimental results for model validation. With some limitations and technical issues to be overcome in the future, the model presented herein clearly demonstrates several advancements based on its features accounting for material viscoelasticity, heterogeneity, and cohesive zone fracture. Potentially, the model can provide significant savings in time and costs and can also be used to improve currently available design analysis tools. [ABSTRACT FROM AUTHOR]

A dynamic analysis based on the spectral element method is described for the interpretation of falling weight deflectometer (FWD) tests on flexible pavements. This dynamic approach was implemented in the computer code Dynamic Analysis of Pavement - Université Laval (DYNAPAV-UL) that includes both frequency-independent hysteretic damping and frequency-dependent viscous damping material models. A parametric study was conducted on a four-layer flexible pavement to evaluate the influence of different layer moduli on deflection basins and deflection histories. The viscous behaviour of the asphalt concrete layer was also investigated. While the deflection basin currently used in static methods gives some details of the pavement response under transient loading, the simulations of FWD tests using the dynamic model suggest that the time histories should be included as well for the interpretation of FWD deflection measurements. In fact, important dynamic phenomena due to inertial effects and viscous effects are only revealed by deflection histories. [ABSTRACT FROM AUTHOR]

This paper presents constitutive design considerations for a semi-rigid, resin-impregnated fiberglass grid that enhances the mechanical performance of an asphalt concrete overlay and provides a pattern to retard crack propagation. An acrylic polymer resin covers the grid-structured fiberglass strands, thus making their viscoelastic nature compatible with the asphalt materials. The remarkable temperature susceptibility of the resin is observed using time-temperature superposition. The grid tensile strength of 100 kN/m was qualified using standard measurements. Three-point bending and cyclic fatigue loading mechanical tests affirm the retardation performance of the grid-reinforced system in terms of crack propagation. The retardation mechanism is affected by synchronizing the cracking pattern with the flexural stress-strain profile through image analysis. A National Center for Asphalt Technology full-scale road testing program provides assessment of the grid-reinforced pavements. A visual inspection of the grid extracted from the traffick zone showed fair condition of the pavement. Cet article présente les facteurs constitutifs de conception d’une grille semi-rigide en fibres de verre imprégnées de résine qui augmente le rendement mécanique d’un revêtement en béton asphaltique et qui permet de réduire la propagation des fissures. Une résine de polymère acrylique recouvre les brins de fibres de verre formant une grille, rendant ainsi leur nature viscoélastique compatible avec les matériaux asphaltiques. La susceptibilité remarquable à la température de la résine est observée en utilisant une superposition temps-température. La résistance à la traction de 100 kN/m de la grille a été quantifiée en utilisant des mesures normalisées. Les essais mécaniques de flexion à trois points et de charges de fatigue cyclique confirment l’efficacité de ralentissement de la propagation des fissures offerte par le système renforcé par une grille. Le mécanisme de retardement est s’effectue en synchronisant le patron de fissuration avec le profile contrainte-déformation en flexion grâce à l’analyse d’images. Un programme d’essais à pleine échelle sur route du National Center for Asphalt Technology permet l’évaluation des chaussées renforcées par ces grilles. Une inspection visuelle de la grille extraite d’une zone soumis au trafic a montré un état acceptable de la chaussée. [ABSTRACT FROM AUTHOR]

A micromechanical-based finite element (FE) model was used to predict the dynamic complex modulus ( E*) of the hot-mix asphalt (HMA). The microstructure of HMA was captured with a high resolution scanner. Two material phases (aggregates and sand mastic) of HMA were modelled with finite elements. The sand mastic herein was composed of fines and asphalt binder with some fine aggregates. The dynamic complex modulus of the sand mastic under different temperatures and loading frequencies was measured in an experimental program. The corresponding principles were applied to bridge the elastic simulation and viscoelastic behavior with the input of the viscoelastic mastic properties. The input parameters in the FE model include the dynamic complex modulus of the sand mastic, the elastic modulus of the aggregates, and the microstructure of the HMA. The E* values of the HMA were measured and used to compare the E* predicted from the FE model. It is found that the FE approach used in this paper has the ability to predict HMA dynamic modulus across a range of temperatures and loading frequencies. The FE prediction of the E* was compared with a recently developed discrete element modelling approach and found the E* prediction from these two approaches to be very similar. [ABSTRACT FROM AUTHOR]

Fatigue of bituminous asphalts is one of the main types of pavement destruction. This phenomenon was studied extensively in Europe (RILEM) and in the United States (SHRP). There are no standardized tests in Quebec to assess asphalt fatigue resistance. In France, a new approach based on the determination of damage rates due to fatigue has been developed for a tension–compression test on asphalt core samples to study their fatigue strength. This paper presents a summary of the knowledge on asphalt fatigue. Damage rate analyses, developed by the DGCB (Département de Génie Civil et du Bâtiment) of the ENTPE at Lyon, is detailed and applied to stone matrix asphalt (SMA). Results show the validity of the approach by damage and the good fatigue damage strength of the SMA. [ABSTRACT FROM AUTHOR]