What is Faulting in Concrete Pavement?
Faulting is the difference in elevation across a joint or crack in a concrete pavement. The PAVER manual for concrete airfields describes it as a difference in elevation at a joint or crack, caused by upheaval or consolidation. The FHWA manual for the Long-Term Pavement Performance (LTPP) program uses almost the same words.
How it is measured
The LTPP manual records faulting in millimetres, to the nearest millimetre, with an FHWA-modified Georgia faultmeter. The surveyor takes three readings at each location and records a representative one. If the approach slab is higher than the departure slab, the value is positive. If it is lower, the value is negative. The manual defines no severity levels for faulting. It prefers a full record of measurements.
The PAVER manual measures the difference in elevation with a straightedge or a level. It counts a fault between two slabs as one slab. It does not rate an elevation difference that comes from construction.
Severity in the PCI survey
PAVER lists faulting as distress 71, “Settlement or Faulting”. The severity depends on the difference in elevation.
| Severity | Runways and taxiways | Aprons |
|---|---|---|
| Low | under 6 mm | 3 to 13 mm |
| Medium | 6 to 13 mm | 13 to 25 mm |
| High | over 13 mm | over 25 mm |
Faulting also sets the severity of other distresses. In the LTPP manual a corner break with faulting of 13 mm or more is high severity. For a transverse crack the limit is 6 mm.
Causes
FAA AC 150/5380-6C gives the cause as upheaval or non-uniform consolidation of the layers under the slab. It names loss of fines, frost heave and swelling soils. The same section describes pumping, the ejection of water and underlying material through joints or cracks. Pumping near a joint indicates poor load transfer, a poor joint seal, or ground water. FHWA states that jointed concrete pavement without an effective load-transfer device typically has faulting and pumping. PAVER lists faulting among the signs of expansion from alkali-silica reaction.
For airfield inspection
AC 150/5320-6G treats joint faulting as a sign that support under the slab may be lost. A structural evaluation looks for this near joints and panel corners. Diamond grinding can restore the surface profile of a rigid pavement.
Frequently Asked Questions
- How do surveyors measure faulting?
- In the FHWA Long-Term Pavement Performance (LTPP) program, faulting is measured with an FHWA-modified Georgia faultmeter, to the nearest millimetre. The surveyor takes three readings at each location and records a representative one. The PAVER method for airfields uses a straightedge or a level to measure the difference in elevation.
- What causes faulting in concrete?
- Upheaval or non-uniform consolidation of the layers under the slab causes it. FAA AC 150/5380-6C names loss of fines, frost heave and swelling soils as causes. A joint without an effective load-transfer device is prone to faulting and pumping.
- How does the PCI method rate faulting?
- The PAVER method rates faulting as settlement or faulting, distress 71, by the difference in elevation. On runways and taxiways, low is under 6 mm, medium is 6 to 13 mm and high is over 13 mm. On aprons the limits are 3 to 13 mm, 13 to 25 mm and over 25 mm.
References
- fhwa-ltpp-dim
- Distress Identification Manual for the Long-Term Pavement Performance Program (Fifth Revised Edition), FHWA-HRT-13-092 FHWA
- paver-concrete
- PAVER Distress Identification Manual, Concrete Surfaced Airfields US Army Corps of Engineers
- faa-ac-150-5380-6c
- AC 150/5380-6C, Guidelines and Procedures for Maintenance of Airport Pavements 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.
