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Asphalt emulsions and cutbacks are mainly used for surface preservation treatments and as bonding layer during pavement construction. Cutback and emulsion residues are routinely evaluated to ensure specification compliance for quality control and assurance purposes. The current test methods for residue recovery of asphalt emulsions and cutbacks are resource intensive, have a low throughput, and require distillation apparatus with a large lab footprint. This study developed two separate test methods that are simple and repeatable for emulsion and cutback residue recovery using a vacuum oven with the ultimate goal that these tests can be used for routine testing. These methods recover small quantity of the residue that is adequate to perform one test with 25 mm plate using dynamic shear rheometer (DSR). This study examines the repeatability of the new method by (1) using a variety of different grades obtained from different suppliers for both cutbacks and emulsions; and (2) participation of two laboratories with different brands of equipment. The mass loss during the residue recovery and the DSR parameter G*/sinδ were used to examine repeatability. The results show that the test methods developed are repeatable between the replicates and between the two participating research laboratories. [ABSTRACT FROM AUTHOR]

Asphalt pavement rutting is caused primarily by shear stresses induced by heavy truckloads. Many tests have been developed to determine asphalt mix rutting potential. However, due to limited correlation with field rutting performance, long testing hours, and difficulties of sample fabricating, no test can be used as a fast and straightforward assessment tool for quality control or quality assurance/acceptance (QC/QA) purpose. In this study, a shearing fixture was developed to investigate the shear rutting potentials of the asphalt mixture more easily and rapidly. An analytical solution was derived from the mechanical analysis. With this solution, the stress distributions of the specimen under the shear loading were analyzed and plotted. These stress distribution plots are also compared with those under the other loading fixtures, such as the indirect tension (IDT) fixture and Marshall fixture. The comparison indicates that the developed shearing fixture is good at inducing shear stress to the specimen and manifesting the shear rutting mechanism. Several scenarios were evaluated by varying the loading fixture configurations, such as the bottom support arc length and angle. The impacts of these configuration elements on the stress distribution were investigated. Laboratory-mixed and laboratory-molded specimens were tested using the shearing fixture, and the test results show high repeatability. The mechanical analysis and experiments indicate that the new shear rutting test is very promising for evaluating the asphalt mix rutting potential quickly and straightforwardly. [ABSTRACT FROM AUTHOR]

The relaxation modulus E(t), creep compliance D(t), and complex modulus [E.sup.*](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 'LVE-master'. The simplicity and accuracy of this new interconversion software was demonstrated through a series of interconversions among HMA LVE functions. Key words: interconverstion, prony series, complex modulus, relaxation modulus, creep compliance, linear viscoelastic, LVE, HMA. Le module de relaxation E(t), la conformite de fluage D(t) et le module complexe [E.sup.*](ω) sont des fonctions souvent utiliseees pour caracteriser le comportement viscoelastique lineaire (LVE) d'asphalte melange; a chaud (HMA). Des conversions entre ces fonctions LVE sont souvent requises. Pour realiser une conversion, une des etapes cle est d'exprimer la source et la cible des fonctions LVE en representations de series de Prony. Pour obtenir les coefficients correspondants des series de Prony, la meethode de collocation et la meethode des moindres carres lineeaires ont souvent ete utilise;es dans le passe. Toutefois, le probleme rencontre; dans ces deux meethodes est qu'il faut manuellement assigner certains coefficients des series de Prony; il en decoule des coefficients de Prony non reealistes ou negatifs ainsi qu'une grande divergence entre les donnees ajusteees et les donnees originales. Pour aborder ce probleeme, le present article montre un nouvel algorithme developpe en incorporant la meethode Levenberg-Marquardt. Ce nouvel algorithme preesente quatre caracte;ristiques uniques: (1) permettre a tous les coefficients des series Prony d'etre librement ajustables, (2) garantir que tous les coefficients des series Prony sont positifs, (3) determiner tous les coefficients des series de Prony automatiquement et simultaneement, et (4) assurer une conversion trees precise par le fait que la courbe d ' ajustement coincide presque compleetement avec la courbe originale. De plus, afin de faciliter l ' implantation et une utilisation pratique, ce nouvel algorithme a ete incorpore dans un logiciel autonome base sur Windows nommee << LVEmaster >>. La simplicite; et la precision de ce nouveau logiciel de conversion ont eete demontrees par une serie de conversions parmi les fonctions LVE des HMA. Mots-cles: conversion, seeries Prony, module complexe, module de relaxation, conformitee de fluage, viscoelastique lineaire, LVE, HMA., Introduction There are several linear viscoelastic (LVE) functions to characterize the behavior of hot mix asphalt (HMA) concrete, such as the relaxation modulus E(t), creep compliance D(t), and complex modulus [...]

As part of a national pool funded study 208 on pavement subgrade performance, 12 full-scale test sections (four soil types and three moisture contents) were constructed and tested under the heavy vehicle simulator (HVS) loading. This paper presents the HVS results on two of the four soils tested: AASHTO Class A-2-4 and A-4 soils, respectively. From the results, it was found that the pavement subgrade performance is a function of soil type, moisture content, and applied stress condition. Additionally, this paper also evaluated the current mechanistic-empirical pavement design guide (MEPDG) subgrade rutting (permanent strain) model through comparing with the actual measurements under the HVS loading. It was found that the MEPDG subgrade permanent strain model needs further improvement, and that a single performance model may not be universally applicable to different subgrade soil types. Consequently, a new permanent strain model for each soil type was developed in this paper, based on the HVS results, and that yielded better predictions. With further validation and field calibration, the proposed models offer promising potential to accurately predict rutting behavior of these two soils. DOI: 10.1061/(ASCE)CF.1943-5509.0000107 CE Database subject headings: Deformation; Subgrades; Soils; Strain; Pavements; Load factors. Author keywords: Rutting; Permanent deformation; Subgrade soil; HVS.

Under the same applied traffic loading, time is traditionally assumed to be a function of only the vehicle speed and the depth beneath the pavement surface. Additionally, no definite loading waveform has been established and/or recommended for any one special loading situation. After numerous computations and analyses in this study, it was found that the loading time is not only a function of the vehicle speed and the depth beneath the pavement surface but is also a function of the moduli ratio between the layer of interest and the immediate succeeding layer below. Furthermore, the loading waveform changed with depth beneath the pavement surface and the moduli ratio. Based on the results of this study, new equations for more accurately determining the loading time were proposed. Additionally, the corresponding loading waveform, which is a function of the depth beneath the pavement surface and the moduli ratio, was recommended. Plausible results were also obtained when an iterated method was introduced to calculate the loading time using the equations proposed in this paper. DOI: 10.1061/(ASCE)TE.1943-5436.0000121 CE Database subject headings: Asphalt pavements; Design; Elasticity; Load factors. Author keywords: Asphalt pavement; Loading time; Loading wave shape; Moduli ratio; Layered linear elastic theory.

The purpose of this paper is to present a new mechanistic-empirical (ME) reflective cracking model developed for hot- mix asphalt (HMA) overlay thickness design and analysis. After reviewing existing models, the reflective cracking model based on Paris' law of fracture mechanics was considered as the state of the practice and was selected as the basis for the ME model development in this study. The model consists of stress intensity factor and fracture properties (A and n) as the fundamental input parameters for modeling reflective crack propagation caused by both traffic loadings (bending and shearing) and thermal effects (temperature variations). For practical application, 32 SIF regression equations were developed for HMA overlays with three levels of load transfer efficiencies (10, 50, and 90%) at joints/cracks under various traffic loading spectrums (bending and shearing) based on more than 1.6 million finite element simulations and computations. For the thermal induced reflective cracking, a 'hybrid' approach, similar to the Strategic Highway Research Program low temperature cracking model, was proposed. In this hybrid approach, the viscoelastic properties of the HMA mixes were considered through the thermal stress at the 'far field' ([[sigma].sub.VE-far]), which then ties with the stress intensity factor ([K.sub.thermal]) determined through regression equations. Also, the required fracture properties (A and n) can easily be determined in the laboratory using the overlay tester that has unique features with respect to specimen size, specimen preparation, and relatively short testing time (about 15 min). Additionally, the proposed reflective cracking model was preliminarily calibrated using three HMA overlay field-case studies, and then verified using California's heavy vehicle simulator test results. Currently, more calibration is underway, but more field performance data are definitely needed for further model calibration and verification. DOI: 10.1061/(ASCE)TE.1943-5436.0000096 CE Database subject headings: Cracking; Stress; Calibration; Pavement overlays. Author keywords: Reflective cracking; Fracture mechanics; Stress intensity factor; Paris' law; Overlay tester.

Abstract: The fundamental mechanisms leading to the development of reflective cracking are differential movements from the supporting pavement structure. In this study, the deflection profiles collected using the rolling dynamic [...]

In laboratory testing of asphalt mixtures, the relationship between the number of load repetitions and permanent deformation has been found to include three distinct stages, namely the primary, secondary and tertiary stages. Similar permanent deformation behavior has also been observed in the field accelerated pavement testing data. It is argued that the three-stage permanent deformation behavior is a basic material property and to comprehensively model asphalt layer behavior, it is necessary to develop a model that accurately characterizes this behavior. In this paper, each of the well-known models critically reviewed appears that they are limited to characterizing only the primary stage. Therefore, a new three-stage model is proposed to describe all three stages. Moreover, an algorithm is established to determine the model parameters from typical laboratory data. The algorithm can also be used to identify the transition point between stages, such as flow number. The proposed model and algorithm are demonstrated through laboratory test results. The analysis results match the field performance. CE Database subject headings: Asphalt mixes; Model verification; Deformation; Laboratory tests.

The Specific Pavement Study-1 pavement test section on US281 in south Texas comprise the largest Strategic Highway Research Program experimental site in the United States. The project was opened to traffic in 1997, and performance has been poor. Three of these test sections developed deep rutting within 1 year. Their surfaces were milled to restore ride quality. Three years after construction, 14 of the sections had 10 mm or more rutting. A forensic study was initiated by the Texas Department of Transportation to identify the cause of the problem. Nondestructive testing was conducted with both the falling weight deflector and ground penetrating radar. No structural problems were detected with either device, both indicating that the base and subbase layers were strong. A field investigation was initiated; the original plan was to cut nine trenches, however, after four trenches were cut, the problematic layer was identified and the trenching operation was terminated. Dynamic cone penetrometer, stiffness gauge, seismic pavement analyzer, and nuclear density gauge tests were then conducted on top of the base and subgrade layers. The trench profiles indicated that the rutting was coming primarily from the top 50-mm (2-inch) asphalt-concrete layer. Asphalt cores were taken from both rutted and nonrutted sections and bag samples of the base were tested in laboratory. The binder was recovered, and the asphalt content and penetration, aggregate gradation, and type were determined. The cause of the problem was traced to a change in aggregate screening, and also an excess of asphalt in the top layer. CE Database subject headings: Forensic engineering; Failure investigations; Texas; Pavements; Stiffness.