Effect of temperature and time on the stiffness properties of HMAC in flexible pavements.

摘要

Surface deflections and backcalculated layer moduli of flexible pavements are significantly affected by the temperature of the asphalt concrete (AC) layer. The correction of these deflections and moduli to a reference temperature requires the determination of an effective temperature of the AC layer. In light of this, a new temperature prediction model for determining the AC temperature on the basis of a database approach is presented, and temperature correction factors for AC modulus are developed. Temperature data points (317) and deflection profiles (656) were collected from six in-service test sites in Michigan. Temperature data points (197) from three of the test sites were used to develop the temperature prediction model, and data from the remaining sites were used for validation. The developed temperature prediction model has a R 2 greater than 90% and an F-statistic significantly greater than 1.0. For further validation of the temperature prediction model, temperature data points (18444) from seven Seasonal Monitoring Program (SNP) sites (Colorado, Connecticut, Georgia, Nebraska, Minnesota, South Dakota, Texas) were obtained from the LTPP Database (DATAPAVE 2.0). The validation results suggest that the model could be adopted to all seasons and other climatic and geographic regions. The major improvements over existing models are: (a) the model does not require temperatures for the previous 5 days, (b) it takes into account temperature gradients due to diurnal heating and cooling cycles, and (c) it needs fewer parameters than other published models. The effect of temperature prediction error on the performance prediction was also investigated. Temperature profiles obtained from the temperature prediction and correction study were used in the following structural analysis.; The temperature-dependent behavior of flexible pavement is due to viscoelastic properties of the AC layer. Hence, in the second part of this study, 2-D and 3-D finite element analyses (FEA) of flexible pavements were performed to investigate the influence of realistic temperature distributions and dynamic loads on pavement responses (mainly, stress, strain, and dissipated energy). Parametric studies (AC thickness, base stiffness, loading condition, and temperature distribution across the AC layer) were first conducted with a 2-D axisymmetric finite element (FE) model. Effects of three temperature distributions (night, morning, and day) and three loading types (load case I—uniform vertical load over the entire load area, load case II—uniform vertical load only under tire treads, and load case III—measured vertical and lateral stresses under tire treads) on the structural response were further investigated with a 3-D FE model. The evaluations from 2-D and 3-D analyses were consistent. These results could explain the occurrence of top-down cracking in AC pavements under certain conditions, and contribute to the development of an improved performance model and/or asphalt pavement design program based on advanced material characterization and dynamic loads.