Department of Transportation
for Road and Bridge Construction
NJDOT B-7 – Determining Optimum Asphalt Content for
Open-graded Friction Course (OGFC)
- 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.
- Apparatus. Use the following apparatus:
- Ovens capable of maintaining temperatures as specified in this method.
- Clear glass (Pyrex) 9-inch diameter pie pans.
- Procedure. Perform the following steps:
- Heat aggregate to 275 °F. Heat molds to 275 °F. Heat binder to the manufacturer’s recommended mixing temperature.
- 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.
- Place each 1000-gram batch into a clean, clear glass (Pyrex) 9-inch pie pan.
- Place samples in an oven at 255 ± 5 °F for 1 hour. Remove and let cool for 1 hour at room temperature.
- Visually observe the amount of liquid asphalt on the bottom of each pan.
- 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.
- Report. Report the asphalt contents tested, the observations for each asphalt content, and the optimum asphalt content determined in Step 6.
Last Document Correction:
December 14, 2007