Lesson 5/Learning Event 3
Percent Voids Filed with Asphalt
The percent voids filled with asphalt is the ratio between the volume of asphalt in the mix and
the volume of voids in the aggregate expressed in percent.
Example. Refer to Figure 13. Assume 20 percent of the volume of the specimen is the volume
of the voids in the aggregate. Fifteen percent of the total volume of the specimen is filled with
asphalt (assuming 5 percent voids total mix). Therefore, 15/20 x 100 = 75 percent of the total
voids are filled with asphalt Generally for surface course the percent voids filled should be
between 70 and 80 percent.
FIGURE 13. PERCENT VOIDS FILLED WITH ASPHALT
DETERMINING THE OPTIMUM ASPHALT CONTENT (OAC)
Test specimens are prepared with at least five different asphalt contents. The values of the
Marshall properties are determined from these samples. The values are then plotted on graphs
(Figures 14 - 17). The graphs and criterion tables (9 and 10) are then used to determine the
optimum asphalt content (OAC).
The following provides an example of the use of the graphs to determine the OAC. The mix is
for a surface course, high pressure tires, and an AGG water absorption rate of less than 2%.