"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.

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.