What is a Leveling Course?
Definition
A leveling course is the first variable-thickness asphalt lift that corrects surface irregularities of an existing pavement before the next course is placed. FAA Item P-401 uses this definition. The P-403 specification also covers “truing and leveling courses”.
What the FAA specifies
- The leveling course follows the aggregate gradation in Table 2 of Item P-401. Gradation 3, which has all material passing the 1/2 inch (12.5 mm) sieve, is the gradation intended for leveling courses.
- The lift may not exceed the lift thickness that Table 2 gives for the gradation. The recommended minimum construction lift thickness for Gradation 3 is 1 1/2 inches (38 mm).
- The leveling course must meet the air-void requirement, but not the mat density and joint density requirements of the surface course. It is compacted with the same effort that reached the density of the control strip.
- The paragraph is for use only where the cross-section must be restored before an overlay. The plans show the areas that need a leveling course.
Where it is used
FAA AC 150/5320-6G names shoving, rutting, scattered settlement and birdbaths as irregularities to correct with profile milling and a leveling course. Over a concrete pavement, a leveling course can be needed where panels are distorted, faulted or settled, or after crack and seat. It can also be needed over a rubblized pavement, depending on the concrete thickness and the base below it.
Leveling course and inspection
A leveling course is a construction step. TarmacView does not place, design or specify it. An airfield inspection can find the surface condition that leads to one, such as rutting and ponding areas. The decision and the design belong to the pavement engineer.
Frequently Asked Questions
- When does an airport overlay need a leveling course?
- When the old surface is uneven, for example with shoving, rutting, settlement or birdbaths. FAA AC 150/5320-6G says to correct these with profile milling and a leveling course. For a concrete pavement that is uneven from panel distortion, faulting or settlement, or after crack and seat, an asphalt leveling course may be required.
- Is a leveling course always needed over rubblized concrete?
- No. FAA AC 150/5320-6G says a leveling course can reduce a rough or uneven rubblized surface. Whether one is required depends on the thickness of the concrete and on the amount and stiffness of the base below it. The AC advises to include an allowance for one in the project.
- What asphalt mix does the FAA use for a leveling course?
- Gradation 3 of Item P-401 in FAA AC 150/5370-10H, the finest of the three gradations, with all material passing the 1/2 inch (12.5 mm) sieve. A note to the table says Gradation 3 is intended for leveling courses and that FAA approval is required to use it elsewhere.
References
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports FAA
- faa-ac-150-5320-6g
- AC 150/5320-6G, Airport Pavement Design and Evaluation FAA
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
