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When employing linear elastic layer analysis, which is widely used for the structural analysis of flexible pavements, it is commonly observed that most critical tensile strains occur at the bottom of an asphalt layer. It is well known that an asphalt mixture is a viscoelastic material, so its response is time and rate dependent; therefore, the results from the elastic assumption may not be borne out in the response of the asphalt layer. This study utilized viscoelastic analysis to identify critical tensile strains and their time-dependent responses. It was found that tensile strains occurred at the bottom and at the top of an asphalt layer and grew because of the theological behavior of an asphalt mixture. As load repetitions continued, the strain at the top showed a higher strain value than the strain value at the bottom. A sensitivity analysis performed on various design parameters indicated that the development of strains at the top and at the bottom is a function of the structural characteristics of pavement structures. Expected trends were observed and findings compared favorably to results of field-calibrated top-down cracking model predictions. DOI: 10.1061/(ASCE)0899-1561(2009)21:7(324) CE Database subject headings: Viscoelasticity; Finite element method; Tensile strain; Cracking; Flexible pavements.

This paper presents the results from an evaluation of a new gradation-based framework developed for identifying and assessing the coarse aggregate structure of dense-graded mixtures for resistance to rutting. A theoretical packing-based analysis procedure was used to evaluate the coarse aggregate structure for hot mix asphalt mixtures. This procedure was applied to an extensive range of mixtures. A key feature of this new framework is the concept of the existence of a dominant aggregate size range (DASR). The porosity of the DASR is calculated based on an interaction diagram to evaluate the degree of particle-to-particle interaction of coarse aggregates between contiguous sieve sizes. In addition, an interaction diagram-based criteria for dense-graded Superpave mixtures are determined, as well as criteria for the porosity of the DASR. Based on the field and laboratory-based rutting performance of the mixtures evaluated in this paper, it was concluded that DASR along with the porosity of the DASR may provide a framework for evaluating the gradation of dense graded mixtures for their likely rutting potential. DOI: 10.1061/(ASCE)0899-1561(2009)21:1(32) CE Database subject headings: Asphalts; Mixtures; Aggregates; Particle size distribution; Porosity; Spacing.

Falling weight deflectometer (FWD) testing has been done extensively in the past to assess structural condition and determine the moduli of pavement layers. The set of modulus values for pavement layers obtained from the backcalculation process may not be accurate even though the computed and measured deflection basin may match within tolerable limits. Extensive interpretation is involved in obtaining the layer moduli of these pavements. Guidelines and tools are provided for calculating layer moduli for flexible pavements. FWD interpretation has become increasingly challenging because more and more of our roads have experienced multiple milling operations and overlays. The characteristics of the structure such as damaged layers, thickness variation, and temperature changes can overwhelm the deflection data, having a far more significant effect than those induced by structural layer stiffness. This study emphasizes that proper interpretation of FWD data involves a complete evaluation of all available data, including core data, roadway data, and section-specific distress information. Evaluating multiple FWD measurements along the sections allows for the evaluation of consistency and assures reasonableness of interpretation. DOI: 10.1061/(ASCE)0899-1561(2003)15:1(25) CE Database keywords: Falling bodies; Weight; Pavements; Data analysis.

Load-induced fatigue cracking is one of the primary distress modes in asphalt pavements at intermediate temperatures. The asphalt community is still searching for a reliable methodology to obtain relevant properties of asphalt binder to assess relative cracking performance. This study proposed an enhanced binder fracture energy (BFE) test to determine the fracture tolerance of asphalt binders. The BFE test successfully differentiated unmodified and modified binders based on the characteristics of the true stress-true strain curve. More importantly, binder fracture energy density (FED) quantitatively distinguished rubber-modified, hybrid, and polymer-modified binders. Finally, fracture properties translated well from binder to mixture such that binders with higher FED resulted in higher mixture FED values. Mixture cracking performance was evaluated by using the energy ratio (ER) parameter that is governed by both failure limit (FED) and rate of damage of asphalt mixtures. An excellent correlation was found between binder FED and mixture ER, given binders containing SBS polymer typically lead to a low mixture rate of damage. Therefore, it appears that binder FED obtained from the BFE test can be used to assess relative cracking performance. Future research on binder rate of damage may be necessary to account for new binder modifications. [ABSTRACT FROM AUTHOR]

When hot mix asphalt (HMA) overlays are placed on distressed flexible or rigid pavement, it is only a matter of time before cracks in existing pavement reflect to the new overlay surface. Asphalt rubber membrane interlayer (ARMI) is one type of interlayer system that has been suggested to mitigate reflective cracking in HMA overlay. However, in terms of reflective cracking performance, mixed results were reported. Also, the ARMI layer has the potential to contribute to instability rutting. In this study, composite specimen interface cracking (CSIC) tests were performed on composite specimens constructed with and without the ARMI layer to evaluate its effects on HMA overlay reflective cracking performance. HMA fracture mechanics was employed to characterize the mechanism of ARMI layer effects on HMA overlay reflective cracking resistance. Results indicate that ARMI not only cannot delay reflective cracking, but it also reduces reflective cracking resistance to some extent. [ABSTRACT FROM AUTHOR]

This paper presents the results from an evaluation of a new gradation-based framework developed for identifying and assessing the coarse aggregate structure of dense-graded mixtures for resistance to rutting. A theoretical packing-based analysis procedure was used to evaluate the coarse aggregate structure for hot mix asphalt mixtures. This procedure was applied to an extensive range of mixtures. A key feature of this new framework is the concept of the existence of a dominant aggregate size range (DASR). The porosity of the DASR is calculated based on an interaction diagram to evaluate the degree of particle-to-particle interaction of coarse aggregates between contiguous sieve sizes. In addition, an interaction diagram-based criteria for dense-graded Superpave mixtures are determined, as well as criteria for the porosity of the DASR. Based on the field and laboratory-based rutting performance of the mixtures evaluated in this paper, it was concluded that DASR along with the porosity of the DASR may provide a framework for evaluating the gradation of dense graded mixtures for their likely rutting potential. [ABSTRACT FROM AUTHOR]