New Jersey

Department of Transportation

Standard Specifications

for Road and Bridge Construction

2007

NJDOT B-7 – Determining Optimum Asphalt Content for
Open-graded Friction Course (OGFC)

1. Scope. This test method is used to determine the optimum percent asphalt in an OGFC mixture. The test method uses a visual draindown analysis to determine optimum asphalt content.
   
   
2. Apparatus. Use the following apparatus:
   
   
   1. Ovens capable of maintaining temperatures as specified in this method.
   2. Clear glass (Pyrex) 9-inch diameter pie pans.
   
   
3. Procedure. Perform the following steps:
   
   
   1. Heat aggregate to 275 °F. Heat molds to 275 °F. Heat binder to the manufacturer’s recommended mixing temperature.
   2. Using 1000-gram batches, mix aggregate with asphalt at a minimum of 3 asphalt contents (1 at the estimated JMF asphalt content and 1 each at + and −0.5 percent of the estimated JMF asphalt content). After mixing, check the temperature to ensure that it is 250 ± 10 °F. Cool or reheat as necessary to meet the temperature tolerance.
   3. Place each 1000-gram batch into a clean, clear glass (Pyrex) 9-inch pie pan.
   4. Place samples in an oven at 255 ± 5 °F for 1 hour. Remove and let cool for 1 hour at room temperature.
   5. Visually observe the amount of liquid asphalt on the bottom of each pan.
   6. Select the asphalt content where ample bonding is evident, without having excessive drainage as evidenced by an appearance of unconnected pools of asphalt binder around aggregate points of contact.
   
   
4. Report. Report the asphalt contents tested, the observations for each asphalt content, and the optimum asphalt content determined in Step 6.