What are Lab-Only Measurements in Pavement Assessment?
Definition
A lab-only measurement is a pavement property that is found by testing a sample, not by looking at the surface. The properties are inside the pavement layer, so a camera on the surface does not give them.
“Lab-only” is a plain label that this glossary uses. The FAA documents that we opened do not define it. They name the tests.
Which properties and which tests
FAA specification P-401 (asphalt mix pavement) is the model specification for new asphalt pavement on US airports. It names these tests:
| Property | Test in P-401 | Where the test is made |
|---|---|---|
| Asphalt (binder) content | ASTM D6307 or ASTM D2172, at least twice per day | Plant mix |
| Mat density | Bulk specific gravity of a core by ASTM D2726, divided by the theoretical maximum density | Core, one per sublot |
| Air voids | ASTM D3203 on compacted specimens | Plant mix, each sublot |
| Moisture damage | Tensile strength ratio by ASTM D4867, not less than 80 in the model specification | Mix design |
A core is a cylinder of pavement, at least 5 inches (125 mm) wide, that is cut with a core drill. The QA laboratory that tests the samples must be accredited under ASTM D3666.
P-401 accepts a lot by the percentage of material within limits (PWL). The lot is acceptable at a PWL of 90 or more. The lower limit for surface course mat density is 92.8 percent, and the air voids limits are 2.0 to 5.0 percent. A contract can change these values, so read the contract specification for a real project.
What the surface shows
Some distress is a sign of a lab-only property. Bleeding is a film of binder on the surface. FAA AC 150/5380-6C says it is caused by too much binder, low air-void content, or both. Asphalt stripping is moisture in the asphalt that separates the binder from the aggregate. These signs show that a problem exists. They do not give the percent of binder, the density or the air-void content.
The same FAA circular says that visual observation is an inadequate predictor of skid resistance. Friction is also measured with a test.
Other test devices
Ground penetrating radar (GPR) is a non-destructive device. AC 150/5320-6G says it gives a continuous profile of the pavement. It can give a rough estimate of layer thickness and can help to detect stripping, layer separation and moisture. The same circular says that cores of the existing pavement help to find the extent and the possible causes of distress. P-401 measures lift thickness on the density cores.
Use in airfield inspection
A drone survey of the pavement surface finds and measures cracks and other visible distress. A core and a lab test then give the material properties at chosen points. The two give different data, so a survey report must say which data it contains.
Frequently Asked Questions
- Which pavement properties are lab-only?
- Asphalt content, in-place density, air voids and moisture damage are the usual ones. FAA specification P-401 tests asphalt content with ASTM D6307 or ASTM D2172 and bulk specific gravity of cores with ASTM D2726. It tests air voids with ASTM D3203 on compacted specimens and moisture damage with the tensile strength ratio (ASTM D4867).
- Can a drone image give the density of a pavement?
- No source that we opened supports it. FAA P-401 accepts mat density from cores. One core is taken from each sublot, and its bulk specific gravity is divided by the theoretical maximum density of that sublot. An image can show surface distress, such as bleeding, which is caused by too much binder or low air voids. It does not give the value.
- Can ground penetrating radar replace core samples?
- No. AC 150/5320-6G describes ground penetrating radar (GPR) as a continuous profile of the pavement that can give a rough estimate of layer thickness. It can also help to detect stripping, layer separation and moisture. P-401 measures the thickness of each lift on the cores that are taken for density.
References
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports, Item P-401 Asphalt Mix Pavement FAA
- faa-ac-150-5320-6g
- AC 150/5320-6G, Airport Pavement Design and Evaluation FAA
- faa-ac-150-5380-6c
- AC 150/5380-6C, Guidelines and Procedures for Maintenance of Airport Pavements FAA
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
