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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.

Current Florida Department of Transportation specifications limit reclaimed asphalt pavement (RAP) usage to 20% in polymer-modified asphalt (PMA) mixtures, because aged and brittle RAP binder may reduce benefits of polymer modification. Previous studies indicated RAP binder stiffness and RAP gradation were important characteristics related to RAP mixture cracking performance. This study focused on developing guidelines to determine maximum RAP content in PMA mixtures based on these RAP characteristics. Eight RAP sources covering a broad range of RAP binder stiffness and RAP gradation were used to assess the effect of these RAP characteristics on cracking performance. The interstitial component fracture energy (FEIC) which is correlated well with mixture fracture energy (FEmix) was employed as a surrogate for FEmix to assess all RAP mixture combinations, and FEIC was determined by the IC direct tension test. FEmix obtained from Superpave indirect tensile tests was used to evaluate findings from FEIC results. Finer RAP and stiffer RAP was more detrimental to cracking resistance, indicating characterising RAP binder stiffness and RAP gradation was necessary to increase the current maximum RAP content in PMA mixture. Developed guidelines allowed up to 40% RAP depending on RAP characteristics and were validated by the way of full mixture testing. [ABSTRACT FROM AUTHOR]

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.

This study investigated the effect of the distribution of aged binder from reclaimed asphalt pavement (RAP) on the fracture tolerance of recycled asphalt mixtures. Two RAP sources (one coarse, one fine), one virgin polymer-modified asphalt binder, and four RAP contents (0 %, 20 %, 30 %, and 40 %) were used to produce a total of seven mixtures. Fracture tolerance was assessed in terms of fracture energy density (FED) at three levels: binder, interstitial component (IC) (composed of effective binder and fine aggregate fraction), and mixture. Binder fracture energy tests were conducted to measure the FED of blends of virgin and recovered RAP binder. IC direct tension tests were employed to determine the IC FED. Finally, Superpave indirect tensile fracture tests were performed to obtain the FED of RAP mixtures. FED decreased with increasing RAP content at the three levels (binder, IC, and mixture). More importantly, IC and mixture exhibited almost identical FED reductions in relative terms, while the reduction was less significant at binder level. This finding indicates that the full blending scenario artificially created at the binder level did not occur at IC and mixture levels. Furthermore, the coarse RAP yielded greater FED than the fine RAP, which substantiates that RAP gradation controls the distribution of RAP binder in recycled mixtures. Consequently, the lower content of aged RAP binder in the IC portion for mixtures with the coarser RAP resulted in better fracture tolerance. The application of a newly developed guideline for determining the maximum allowable RAP content in recycled mixtures confirmed that the coarser RAP used in this study allows for a greater RAP content than the finer RAP despite the stiffer RAP binder. [ABSTRACT FROM AUTHOR]

Previous research indicated that color variation, specularity, and porosity, which are not related to surface roughness or texture of aggregate, affect the value of Texture Index (TI) determined using standard procedures associated with Aggregate Image Measurement System (AIMS). In response, a new technique called Photometric Stereo-Independent Component Analysis (PS-ICA) was developed and found to effectively mitigate color variation effect. Reduced light intensity was found to partially, but not completely, mitigate specularity effect. However, effect of pores could not be mitigated with measurements obtained from existing AIMS procedures. An extensive evaluation was conducted on a broad range of aggregates to determine whether TI values obtained before and after polishing using PS-ICA and reduced light intensity resulted in appropriate assessment of polishing resistance. For aggregates exhibiting strong specularity, it was found that specularity effect increased after initial polishing, which increased TI, thereby confounding and sometimes overwhelming the reduction in TI associated with reduced roughness. The specularity effect appeared to remain constant after initial polishing, such that further polishing resulted in a more consistent reduction in TI. For aggregates not exhibiting specularity, reduction in PS-ICA TI after initial polishing was found to be an excellent parameter to assess polishing resistance. [ABSTRACT FROM AUTHOR]