"TRB's National Cooperative Highway Research Program (NCHRP) Report 531: Relationship of Air Voids, Lift Thickness, and Permeability in Hot-Mix Asphalt Pavements provides guidance for hot-mix asphalt pavement construction designed to achieve satisfactory levels of in-place air voids and permeability. This guidance was developed from the findings of a research project that examined the relationship of air voids content to permeability and hot-mix asphalt lift thickness. The full finding of the research were published as NCHRP Web Document 68"--Publisher's description.
The water permeability of asphalt pavements has been of interest to both researchers and practitioners because the ingress of water into the pavement and its impact within pavement layers can potentially result in moisture induced damage and pavement premature failure. The uncertainty and diversity of permeability in asphalt pavements have motivated scholars to investigate various test methods to reliably determine pavement permeability and the coefficient of permeability. An important question related to such testing is whether the permeability of laboratory prepared specimens can be correlated to the permeability of constructed pavement. If such a correlation can be developed, determining the permeability of laboratory prepared specimens could be included as part of the asphalt mix design process. It has been the focus of the research presented in this thesis to investigate existence of such correlation and to determine if the permeability of lab-compacted specimens can be applied to predict the permeability of field compacted specimens. This research exploits an experimental approach to derive the correlation. This study tested three sets of asphalt concrete mixes from three different counties in Pennsylvania representing three mixes with different aggregate gradations and types, and with different asphalt binder contents. The sets included field cores from constructed pavements as well as loose materials obtained behind the paver. The loose mixes were compacted in the laboratory to prepare specimens. Test results indicated that the permeability of field cores with a 12.5 nominal maximum aggregate size have a reasonable relationship with the permeability of corresponding lab compacted specimens. However, the two other mixes with 9.5 mm nominal maximum aggregate size had significantly lower permeability and did not exhibit a meaningful relationship between the permeability of field cores and lab compacted specimens. Finally, this research also investigated the impact of aggregate size, gradation, specimen thickness, and air void on the permeability of Hot Mixed Asphalt.
TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 537: Impact of Asphalt Thickness on Pavement Quality documents transportation agency policy for lift thickness and minimum compaction requirements on resultant asphalt pavement quality. To achieve expected pavement performance, it is important that asphalt concrete (AC) have adequate density. A critical factor in achieving this density is the ratio of lift thickness to nominal maximum aggregate size (t/NMAS). The information in the report is designed to help make agencies aware of a range of practices other agencies use to achieve a desired t/NMAS ratio, ensuring that density of AC is adequate to meet expected pavement performance.
