Density is one of the most important parameters in construction of asphalt mixtures. A mixture that is properly designed and compacted will contain the optimum amount of air voids. Because density of an asphalt mixture varies throughout its life, the voids must be lowenough initially to prevent permeability of air and water and high enough after a few years of traffic to prevent rutting caused by plastic flow. There are three primary methods of specifying density: (a) percent of control strip, (b) percent of laboratory density, and (c) percent of theoretical maximum density (tmd). If used correctly, all three methods can result in satisfactory compaction. The initialin-place air voids must be below approximately 8% and are determined by comparing bulk density and tmd. The final in-place air voids, which must be above approximately 3%, are estimated by comparing the bulk density of laboratory-compacted samples and the tmd. The two methods that have been used to measure bulk density of asphalt mixtureare physical measurements of cores and use of the nuclear gauge. The nuclear gauge is fast and nondestructive but is not as accurate asthe core method. This paper appears in transportation research record no. 1282, Transportation construction 1990.
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