Calculating the quotient of the bulk and maximum (the so-called theoretical maximum density [TMD] or the Rice density after ASTM 2041) densities is a popular method of determining the compaction factor. The requirement for compaction of an SMA layer is a minimum 94% (of the maximum density) according to the NAPA SMA Guidelines QIS 122; that makes upto 6% (v/v) of air voids allowable after compaction. In this case the reference density does not depend on conditions for preparing laboratory specimens. As in the previous method, densities obtained in a laboratory during mix design are not taken into account; results from testing the density of a mixture taken from an asphalt plant during trial production are recorded.
The essential strength of that method is making the compaction factor free from various conditions for preparing specimens. The possibility of making mistakes in determining the reference density in a laboratory obviously disappears.
