What is the Superpave Gyratory Compactor (SGC)?
Definition
The Superpave gyratory compactor (SGC) is a laboratory machine that compacts hot mix asphalt samples to prepare them for mix design tests. ASTM D6925 is the test method for preparing these specimens and determining their relative density.
Use in airport pavement specifications
FAA specification Item P-401, Asphalt Mix Pavement, gives two ways to compact the laboratory samples for the job mix formula (JMF). One is a Marshall compactor, per ASTM D6926. The other is the gyratory compactor, per ASTM D6925. The engineer chooses the method for the project. An accredited laboratory prepares the JMF. Item P-403 offers the same two methods.
The design criteria in the P-401 Table 1 do not depend on the method. The table gives the number of blows or gyrations, and a design air void content of 3.5 percent. The guidance note says to specify 75 blows or gyrations for airports that serve aircraft heavier than 60,000 pounds. It says 50 may be specified for aircraft of 60,000 pounds or less.
Relevance to airfield inspection
The SGC works in a laboratory on mix samples. It is not a method to inspect a pavement that is in service. A condition survey of a pavement looks at its surface distresses, not at its mix design.
Frequently Asked Questions
- What is the Superpave gyratory compactor used for?
- A laboratory uses it to prepare compacted samples of hot mix asphalt. Technicians test the samples to develop the job mix formula (JMF), which is the mix design for a project. ASTM D6925 covers the preparation of the samples and the determination of their relative density.
- Does the FAA require the gyratory compactor for airport asphalt?
- No. FAA specification P-401 lets the engineer choose between two methods. One is a Marshall compactor (ASTM D6926). The other is the gyratory compactor (ASTM D6925). The design criteria in the specification's Table 1 are the same for both.
- How many gyrations does the FAA specify?
- The FAA guidance note says to specify 75 blows or gyrations for airports that serve aircraft heavier than 60,000 pounds. It says 50 may be specified for aircraft of 60,000 pounds or less. Table 1 gives 3.5 percent design air voids.
References
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports FAA
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