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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.

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.