Elisabete Fraga de FreitasPaulo PereiraLuis Picado-SantosA. Thomas Papagiannakis...
p.174-182页
查看更多>>摘要：Top-down cracking (TDC) is a flexible pavement distress caused by a number of factors, including high contact stresses from truck tires, mix design characteristics (e.g., binder type and aggregate gradation), and poor construction quality (e.g., segregation and compaction methods). This paper presents the findings of a study seeking to quantify the effect of those factors on TDC. The study consists of a laboratory component involving an accelerated wheel-tracking device and a modeling component involving a 3-D nonlinear viscoelastic finite element model. The laboratory component of the study involved 17 asphalt bituminous slabs constructed to simulate the variation in material properties observed in the field as part of an earlier forensic TDC study. The effect on TDC of air voids, bitumen content and type, aggregate gradation, and segregation were studied under three temperature conditions. Air voids, segregation, and binder content were found to have a significant effect on TDC for all temperatures tested. Modeling the TDC involved laboratory testing to establish the viscoelastic and tensile strength properties of the asphalt mixtures tested. It was found that the rutted surface contributes significantly to TDC initiation.
Michael P. WagonerWilliam G. ButtlarGlaucio H. PaulinoPhilip Blankenship...
p.183-192页
查看更多>>摘要：In recent years the transportation materials research community has focused a great deal of attention on the development of testing and analysis methods to shed light on fracture development in asphalt pavements. Recently it has been shown that crack initiation and propagation in asphalt materials can be realistically modeled with cutting-edge computational fracture mechanics tools. However, much more progress is needed toward the development of practical laboratory fracture tests to support these new modeling approaches. The goal of this paper is twofold: (a) to present a disk-shaped compact tension [DC(T)] test, which appears to be a practical method for determining low-temperature fracture properties of cylindrically shaped asphalt concrete test specimens, and (b) to illustrate how the DC(T) test can be used to obtain fracture properties of asphalt concrete specimens obtained from field cores following dynamic modulus and creep compliance tests performed on the same specimens. Testing four mixtures with varied composition demonstrated that the DC(T) test could detect the transition from quasi-brittle to brittle fracture by testing at several low temperatures selected to span across the glass transition temperatures of the asphalt binder used. The tendency toward brittle fracture with increasing loading rate was also detected. Finally, the DC(T) test was used in a forensic study to investigate premature reflective cracking of an isolated portion of pavement in Rochester, New York. One benefit of the DC(T) test demonstrated during testing of field samples was the ability to obtain mixture fracture properties as part of an efficient suite of tests performed on cylindrical specimens.
查看更多>>摘要：The importance of aggregate characteristics has been emphasized in the Superpave~® asphalt mixture design procedure. However, criteria for guidelines for the selection of suitable aggregate gradations—other than gradation limits for different nominal maximum size aggregate blends, including the restricted zone—have been neglected. With the move toward mechanistic-empirical pavement design, the dynamic modulus is used to account for mixture properties in the pavement design. It is of significant importance to mix designers to possess a framework for determining how to optimize a mixture for ensuring an adequate dynamic modulus. This paper presents the results from a study of the effects of gradation characteristics on the dynamic modulus. Power law-based gradation factors are obtained for 13 aggregate gradations (coarse and fine graded) composed of limestone and granite aggregates. These gradation factors were used to identify and evaluate relationships between gradation factors and the dynamic modulus at higher temperature (40℃). Subsequently, a tentative framework was established for optimizing mixture gradations for dynamic modulus values. Findings illustrate that gradation factors based on power law parameters can be used to optimize mixture gradations for key mixture properties, such as the dynamic modulus. Results also demonstrate the critical nature of aggregate gradation in achieving desired mixture properties.
查看更多>>摘要：The new 2002 AASHTO guide for the design of pavement structures is based on mechanistic principles and requires the dynamic modulus as input to compute stress, strain, and rutting and cracking damage in flexible pavements. The 2002 AASHTO guide has three different levels of analysis; the level used depends on the importance of the pavement structure in question. Dynamic modulus testing is required for Level 1 pavement analysis, whereas no laboratory test data are required for Level 2 and Level 3 pavement analysis. Instead, a predictive dynamic modulus equation is used to generate input values. It is of significant importance to state agencies to understand how well the dynamic modulus for locally available materials compares with the predicted dynamic modulus. This paper presents the results of a study by the Florida Department of Transportation and the University of Florida that focused on the evaluation of the dynamic modulus predictive equation used in the new AASHTO 2002 guide for mixtures typical to Florida. The resulting research program consisted of dynamic modulus testing of 28 mixtures common to Florida. Results showed that on average the predictive modulus equation used in the new AASHTO 2002 flexible pavement design guide appeared to work well for Florida mixtures when used with a multiplier to account for the uniqueness of local mixtures. Results of the study also identified optimal viscosity-temperature relationships that result in the closest correspondence between measured and predicted dynamic modulus values.
查看更多>>摘要：A dynamic modulus master curve for asphalt concrete is a critical input for flexible pavement design in the mechanistic-empirical pavement design guide developed in NCHRP Project 1-37A. The recommended testing to develop the modulus master curve is presented in AASHTO Provisional Standard TP62-03, Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures. It includes testing at least two replicate specimens at five temperatures between 14℉ and 130℉ (-10℃ and 54.4℃) and six loading rates between 0.1 and 25 Hz. The master curve and shift factors are then developed from this database of 60 measured moduli using numerical optimization. The testing requires substantial effort, and there is much overlap in the measured data, which is not needed when numerical methods are used to perform the time—temperature shifting for the master curve. This paper presents an alternative to the testing sequence specified in AASHTO TP62-03. It requires testing at only three temperatures between 40℉ and 115℉ (4.4℃ and 46.1℃) and four rates of loading between 0.01 and 10 Hz. An analysis of data collected using the two approaches shows that comparable master curves are obtained. This alternative testing sequence can be used in conjunction with the simple performance test system developed in NCHRP Project 9-29 to develop master curves for structural design.
查看更多>>摘要：An extension of the discrete element modeling (DEM) approach, or clustered DEM, was used to simulate the hollow cylinder tensile (HCT) test, in which various material phases (e.g., aggregates, mastic) are modeled with bonded clusters of discrete elements. The basic principle of the HCT test is the application of internal pressure to the inner cavity of a hollow cylinder specimen, which produces circumferential strain. In the present study an experimental program was conducted to measure the complex modulus of asphalt concrete mixtures at various loading rates and temperatures. The HCT test was then modeled with a two-dimensional, linear elastic DEM simulation. The current approach uses the correspondence principle to bridge between the elastic simulation and viscoelastic response. The two-dimensional morphology of the asphalt concrete mixture was captured with a high-resolution scanner, enhanced with image-processing techniques, and reconstructed into an assembly of discrete elements. The mixture complex moduli predicted in the HCT simulations were found to be in good agreement with experimental measurements across a range of test temperatures and loading frequencies for the coarse-grained mixtures investigated. Ongoing work in the area of viscoelastic constitutive modeling, fracture modeling, and three-dimensional tomography and modeling will extend the capabilities of this promising technique for fundamental studies of asphalt concrete and other particulate composites.
查看更多>>摘要：The primary purpose of this paper is to demonstrate the applicability of the three-stage Weibull equation to describe the fatigue damage process using flexural controlled deformation fatigue tests. A data set of 179 beam fatigue tests originally designed for exploring the fatigue performance of conventional dense graded asphalt concrete (DGAC) and asphalt-rubber hot-mix gap-graded (ARHM-GG) mixes was used to inspect the three-stage Weibull parameters that were estimated using a genetic algorithm. The tree-based regression-category models were then used to uncover the data structure of the estimated parameters as a function of material properties, conditioning methods, temperatures, compaction methods, and strain levels. In general, the three-stage Weibull equation provides satisfactory fitting results for the three-stage fatigue damage process occurring in a beam test. It was found that the tree-based models of three-stage Weibull parameters associated with the crack initiation stage were statistically adequate and reliable compared with the models of parameters related to the warm-up stage and the crack propagation stage. It might suggest that these crack initiation parameters are better indexes to assess the fatigue performance.
Shane UnderwoodA. Homayoun HeidariMurthy GuddatiY. Richard Kim...
p.238-247页
查看更多>>摘要：Accurate multiaxial characterization of asphalt concrete requires a thorough understanding of its anisotropic behavior. For that purpose a study has been conducted to examine the anisotropic properties of asphalt concrete in the linear viscoelastic range, with growing damage, and during volumetric deformation. Tests were conducted on specimens cored in the vertical and horizontal directions from gyratory-compacted specimens. Anisotropy was found to have no effect on the linear viscoelastic properties of the material. This finding is supported by subsequent results from monotonic constant crosshead rate uniaxial tension and uniaxial compression tests. It was also found that anisotropy contributes greatly to the behavior of asphalt concrete in compression, but shows little, if any, effect on tensile properties. In addition, the strong dependence of anisotropy on temperature and strain rate is presented. Finally, promising results from a simplified method of extracting the anisotropic behavior of asphalt concrete with the use of the hydrostatic test are also introduced.
NETL
NSTL