What is Asphalt Binder Content?
Asphalt binder content is the percentage of the total mass of a hot-mix asphalt mixture that is asphalt binder. The FAA construction specification calls it “asphalt content”.
How it is measured
A laboratory tests a sample of plant-made mix. FAA item P-401 allows ASTM D6307, the ignition method, or ASTM D2172, which extracts the bitumen from the mix. ASTM D4125 is a nuclear method for the same property.
In the ignition method, a furnace at about 538 degrees C burns off the binder. The result needs a correction factor. The laboratory finds it with specimens that it mixed to a known binder content. Fine particles lost in the furnace and aggregate that breaks down in the heat both cause errors. With ASTM D6307, P-401 sets the correction factor at the first test of plant production and again at every tenth test.
What the FAA specification sets
- Mix design. The job mix formula lists the percent of asphalt. The design air voids are 3.5 percent. The design uses 75 blows or gyrations for airports that serve aircraft over 60,000 pounds.
- Production testing. The contractor does at least two asphalt content tests per day. The result for the day is the average.
- Control limits. The limits are around the job mix formula target. For one test result, the action limit is plus or minus 0.45 percent. The suspension limit is plus or minus 0.70 percent.
- Acceptance. P-401 accepts a lot on air voids, mat density, joint density and grade. Asphalt content is a production control, not an acceptance criterion.
What the pavement shows
Too much binder causes bleeding. Bleeding is a shiny, sticky film of binder on the surface. FAA AC 150/5380-6C names excess binder and low air-void content as the causes. Extensive bleeding may severely reduce skid resistance, and it may come before rutting.
Raveling does not point to one cause. AC 150/5380-6C says it may indicate that the binder has aged and hardened.
A surface distress gives a probable cause. It does not give the binder content. Inspectors record these distresses in a Pavement Condition Index (PCI) survey. ASTM D5340 covers airports, and ASTM D6433 covers roads and parking lots.
Frequently Asked Questions
- How is asphalt binder content measured?
- A laboratory measures it on a sample of plant-made mix. FAA item P-401 allows ASTM D6307 (ignition method) or ASTM D2172 (extraction of bitumen from the mix). ASTM D4125 is a nuclear method for the same property. In the ignition method, a furnace at about 538 degrees C burns off the binder. The mass loss gives the binder content after a correction.
- What tolerance does the FAA set for asphalt content?
- The P-401 control charts set limits around the job mix formula target. For one test result, the action limit is plus or minus 0.45 percent. The suspension limit is plus or minus 0.70 percent. For the range of two results, the suspension limit is 0.8 percent. These are production control limits. P-401 does not accept or pay for a lot on asphalt content.
- Does too much binder cause bleeding?
- Yes. FAA AC 150/5380-6C says bleeding is caused by excessive asphalt binder in the mix, low air-void content, or both. Extensive bleeding may severely reduce skid resistance. Bleeding may also come before rutting and wash-boarding.
References
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports FAA
- faa-ac-150-5380-6c
- AC 150/5380-6C, Guidelines and Procedures for Maintenance of Airport Pavements FAA
- faa-paver-asphalt
- Asphalt-Surfaced Airfields Distress Manual (PAVER) FAA
- aashto-resource-ignition-cf
- The Importance of Asphalt Content Ignition Furnace Correction Factors AASHTO Resource
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