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Stone-on-stone contact of the coarse-aggregate fraction is one of the main characteristics of permeable friction course (PFC) asphalt mixtures that is required to provide adequate resistance to both raveling and permanent deformation. Currently, stone-on-stone contact is determined by comparing the air voids content in the coarse aggregate (VCA), assessed in both the dry-rodded condition ([VCA.sub.DRC]) and the compacted PFC mixture ([VCA.sub.mix]). The underlying assumption is that the coarse aggregate of a compacted PFC mixture with [VCA.sub.mix] equal to [VCA.sub.DRC] would develop a stone-on-stone contact condition equivalent to that existing in the dry-rodded aggregate. This study focused on proposing enhancements for the quantitative determination of stone-on-stone contact of PFC mixtures. The assessment supported on both laboratory testing and application of the discrete element method and image analysis techniques, led to recommendation of a criterion to determine the breaking-sieve size. In addition, verification of stone-on-stone contact using a maximum VCA ratio of 0.9 was recommended to ensure the design and construction of PFC mixtures with fully developed stone-on- stone contact. DOI: 10.1061/(ASCE)MT.1943-5533.0000117 CE Database subject headings: Asphalt pavements; Porous media; Aggregates; Mixtures. Author keywords: Asphalt pavements; Porous pavements; Asphalts; Aggregates.

Drainability is one of the main characteristics of permeable friction course (PFC) mixtures and is the primary reason for using these mixtures as the surface course in asphalt pavements in the United States. Current approaches suggested for PFC mix design to evaluate drainability (using gyratory-compacted specimens) include: (1) achieving a target total air void (AV) content as an indirect indication of permeability and (2) direct measurement of permeability in the laboratory. The assessment conducted in this study suggested that these approaches are not effective in ensuring adequate drainability in field-compacted mixtures. Thus, different alternatives were evaluated to improve this assessment. Corresponding analysis suggested that: (1) the water-accessible AV content can be used as a surrogate of the total AV content to indirectly assess permeability and (2) the water flow value (outflow time) can be applied to evaluate the field drainability of PFC mixtures. The expected value of permeability, determined using a modified version of the Kozeny-Carman equation, was recommended to analytically predict permeability for mix design and evaluation purposes. DOI: 10.1061/(ASCE)MT.1943-5533.0000053 CE Database subject headings: Asphalt pavements; Porous media; Permeability; X-rays; Asphalts; Mixture; Friction. Author keywords: Asphalt pavements; Porous pavements; Permeability; X-rays; Asphalts.

This paper evaluates the relationship between the air void distribution in asphalt mixes and their moisture susceptibility. Asphalt mix specimens were prepared to have different air void distributions through using two different gradations, using two different compaction angles in the Superpave gyratory compactor, and trimming the specimens at different locations. An x-ray computed tomography system was used to capture the internal structure of the specimens, and image analysis techniques were used to quantify the air void distribution and connectivity. Specimens in unconditioned (dry) and moisture-conditioned (wet) states were subjected to dynamic loading, and damage was evaluated using a crack growth index based on fracture theory. The parameters required for the crack growth index were obtained from mechanical and surface energy tests. The analysis results clearly demonstrate the influence of air void distribution on moisture susceptibility. Consequently, the analysis method presented in this paper can be used to evaluate alternative mix designs and internal structures, even when the same materials are used, in order to optimize the resistance to moisture damage. DOI: 10.1061/(ASCE)0899-1561 (2007) 19:8(655) CE Database subject headings: Asphalt mixes; Voids; Fracture mechanics; Moisture; Damage assessment; Energy dissipation; Imaging techniques; X rays.

Since the 1960s, a uniform circular vertical contact stress has been used to model the tire/pavement interface in asphalt pavements. Recent experimental measurements show that this assumption cannot be used to model the actual interaction. This study investigated the influence of nonuniform contact stress distribution on the stress distribution and permanent deformation profile in asphalt pavements. A previous study measured the tire contact stresses between the pavement surface and moving pneumatic tires. Material properties of a hot mix asphalt mixture used at WesTrack were obtained from compressive strength tests within the framework of an elastic-viscoplastic constitutive model. A three-dimensional finite element (FE) analysis was performed based on boundary conditions and measured vertical stresses at WesTrack. The tire pressure distribution was dependent on the tire load and significantly influenced the pavement response. The FE analysis based on the elastic-viscoplastic model was able to simulate the measured permanent deformation profiles. CE Database subject headings: Finite elements; Asphalt pavements; Contact pressure; Viscoplasticity; Deformation.

The majority of U.S. departments of transportation (DOT) maintain quality assurance (QA) programs that require asphalt binder testing to verify grade compliance according to Superpave performance grade (PG) specifications. In Texas the binder is tested immediately after binder production, although the goal of QA is to ensure that the binder specified is used during construction. Between production and construction, the material is stored and transferred multiple times before it reaches the construction site or hot mix asphalt (HMA) plant. During this journey, binder properties may change due to many factors and these changes may have a negative impact on performance. To evaluate which factors are detrimental, a laboratory testing program was conducted to simulate the effects of storage time, storage temperature, contamination, and modification on the dynamic shear rheometer (DSR) performance parameter G*/sin[delta] after rolling thin film oven (RTFO) aging. A statistical analysis was performed, and the results indicated that all factors included in the simulation were significant. Results, conclusions, and general recommendations are provided to improve the current TxDOT QA program. DOI: 10.1061/(ASCE)0899-1561(2005)17:1(89) CE Database subject headings: Aging; Asphalt pavements; Binders, materials; Contamination; Quality control; Road construction; Storage tanks; Temperature effects; Texas.

State highway agencies strongly desire to develop and use performance-related specifications (PRS) for highway construction. A PRS for hot mix asphalt (HMA) construction, titled HMA Spec, was recently developed as part of the WesTrack project. The beta version of HMA Spec was applied to compare pay factors and actual rutting performance to predicted performance for four Nevada Department of Transportation (NDOT) test sections on Interstate 80 (I-80) east of Reno, Nevada. Some of these sections were similar in terms of materials and construction techniques to coarse-graded sections constructed at WesTrack, so a comparison to performance at WesTrack was also made. NDOT placed the test sections on 1-80 in an effort to assess the applicability of the Superpave mix design process and HMA Spec for Nevada's conditions. Sections were designed using both Hveem and Superpave mix design methods. Several interesting observations were made while evaluating the HMA Spec output. These observations and field performance data are described in this paper. CE Database subject headings: Asphalt mixes; Specifications; Asphalt pavements; Life cycle cost; Performance evaluation; Case reports; Highway construction.

A new accelerated pavement testing (APT) tool has recently been developed between relatively inexpensive laboratory testing and expensive but more realistic full-scale accelerated load testing. The one-third scale model mobile load simulator (MMLS3) applies a scaled load on a single tire smaller than a standard truck tire used in full-scale devices and can be used for both laboratory and field applications. For two hypothetical and eight actual pavement structures at a location where both full-scale APT devices and the MMLS3 were used, stress analyses were conducted to: (1) explore the hypothesis of comparable stress distribution; and (2) compare theoretical and measured rutting performance toward validating a performance prediction methodology. For the hypothetical pavement structures, the comparable stress hypothesis was upheld. Theoretically calculated rotting ratios based on stress analyses after correcting for differences in loading and environmental conditions were compared with actual measured field rotting ratios. The results were credible and demonstrated that when all influencing factors are taken into account, rutting performance under full-scale loading can be predicted based on MMLS3 results and stress analysis. DOI: 10.1061/(ASCE)0733-947X(2003)129:4(451) CE Database subject headings: Pavements; Full-scale tests; Stress analysis.

The use of high amounts of reclaimed asphalt pavement (RAP) in asphalt pavements has many economic and environmental benefits; however, there are concerns about brittleness and potential cracking of asphalt mixtures. One of the solutions to address this concern is through the inclusion of recycling agents (rejuvenators). The purpose of this study was to explore the effect of different types of recycling agents (biooils, vegetable oils, tall oil, aromatic extract, and paraffinic oil) on the rheological, microstructural, nanomechanical, and chemical properties of asphalt binder blends with high RAP content. Rheological properties were assessed using a dynamic shear rheometer. Atomic force microscopy was used to determine the microstructural characteristics and nanomechanical properties of the asphalt binder blends. A wavelet packet transform approach was proposed to quantify surface roughness characteristics. Fourier transform infrared spectroscopy was used to evaluate the chemical properties based on carbonyl and sulfoxide indices. Results indicated a correlation between the phases observed in the microstructure and rheological performance. Biooil recycling agents were the most effective in improving the microscopic distribution and rheological properties of binder blends, followed by vegetable oils. However, chemical analysis suggested that the addition of recycling agents did not reverse oxidative aging. Finally, the study recommended a rejuvenation index (RI) that quantified the effectiveness of recycling agents in improving blending and reducing stiffness and aging susceptibility. The RI signified that tall oil was the most susceptible to aging, followed by aromatic extract and paraffinic oil, whereas biooils and vegetable oils were the least susceptible to aging. [ABSTRACT FROM AUTHOR]

Warm-mix asphalt (WMA) technologies aid in reducing mixing and compaction temperatures for asphalt concrete mixtures, allowing for savings in fuel consumption and extending haul distances and construction season. The reduced temperatures also provide a greener technology as emissions are lowered at the plant and the construction site. Engineering and environmental benefits promoted the rapid implementation of WMA technologies, but concerns remain regarding the difference in mixture performance of WMA versus hot-mix asphalt (HMA) because of the changes in the production process, specifically in terms of moisture susceptibility. This case study evaluates moisture susceptibility through the use of laboratory tests including the wet indirect tensile (IDT) strength test, the tensile strength ratio (TSR), and the Hamburg wheel tracking test (HWTT) analyzed with a novel methodology. The performance of two WMA technologies (Evotherm DAT and foaming) versus a control HMA is analyzed with and without antistripping additives and/or recycled materials after field and laboratory aging. Findings suggest that the WMA mixtures are more prone to moisture susceptibility in their early life as compared with HMA. The incorporation of recycled materials did not show a clear benefit for the WMA, whereas the inclusion of antistripping additives and aging significantly improved WMA in terms of moisture resistance, rendering mixtures with equivalent performance to HMA. [ABSTRACT FROM AUTHOR]

A new accelerated pavement testing (APT) tool has recently been developed between relatively inexpensive laboratory testing and expensive but more realistic full-scale accelerated load testing. The one-third scale model mobile load simulator (MMLS3) applies a scaled load on a single tire smaller than a standard truck tire used in full-scale devices and can be used for both laboratory and field applications. For two hypothetical and eight actual pavement structures at a location where both full-scale APT devices and the MMLS3 were used, stress analyses were conducted to: (1) explore the hypothesis of comparable stress distribution; and (2) compare theoretical and measured rutting performance toward validating a performance prediction methodology. For the hypothetical pavement structures, the comparable stress hypothesis was upheld. Theoretically calculated rutting ratios based on stress analyses after correcting for differences in loading and environmental conditions were compared with actual measured field rutting ratios. The results were credible and demonstrated that when all influencing factors are taken into account, rutting performance under full-scale loading can be predicted based on MMLS3 results and stress analysis. [ABSTRACT FROM AUTHOR]