15 May 2001
Computation of Optimum Asphalt Content1
Peak of stability curve
Peak of unit-weight curve
4 percent voids in total mix (hot-mix asphalt)
75 percent total voids filled with asphalt (hot-mix asphalt)
Based on data in figure 2-7.
Evaluation of Acceptability of Design Mix
4.6 Percent Asphalt
Flow 0.025 centimeters (0.01 inch)
Less than 16
Stability, kN (psi)
More than 8.0 (1,800)
Percent voids in total mix
3-5 percent (hot-mix asphalt)
Percent total voids filled with asphalt
70-80 percent (hot-mix asphalt)
 Gyratory compaction at 1,380 kPa (200 psi), 1-degree, 30 revolutions shall use
the mix design criteria contained in Sections 1 and 2 of table 2-7 for the 75-blow mix. Additionally, the
mix shall have a gyratory stability index (GSI) equal to or less than 1.
 Gyratory compaction at 1,655 kPa (240 psi), 1-degree, 60 revolutions shall use
the mix design criteria combined in Sections 1 and 2 of table 2-7 or 2-8 for the 75-blow mix. Additionally,
the mix shall have a GSI equal to or less than 1.
(b) If the optimum bitumen content selected by using the design parameters in Sections 1
and 2 of table 2-7 or table 2-8 does not produce a GSI equal to or less than 1, the asphalt content shall
be reduced slightly to meet the GSI requirement.
(c) Laboratory densities, for field control, shall be determined in the field by GTM
compaction or by Marshall compaction correlated to GTM compaction. The correlation will be made as
part of the mix design effort and will result in establishing the required number of Marshall blows to
achieve the same density as the GTM compactor provided there is no significant additional aggregate
breakage with the hand hammer than with the GTM. The correlation may also be established by
determining the difference in unit weight between the GTM compaction curve and the 75-blow Marshall
compaction curve at the desired asphalt content. This difference can be added to the 75-blow field
density for comparison with the GTM density. Laboratory densities for field control can then be
determined using the Marshall hammer.