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.

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.

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%.