What is Transverse Cracking in Pavements?
A transverse crack is a crack in a pavement that runs across it, at about a right angle to the centreline.
Definition
The FHWA Long-Term Pavement Performance (LTPP) manual describes a transverse crack as a crack “predominantly perpendicular to pavement centerline”. The PAVER manual for asphalt airfields (distress 48) gives the same orientation. It adds that the crack lies at about a right angle to the centreline or to the direction of laydown. PAVER is the pavement management system of the US Army Corps of Engineers. ASTM D5340 is the airport pavement condition index method. The PAVER manuals set out its distresses.
PAVER groups longitudinal and transverse cracks in asphalt as one distress, code 48. For concrete, it groups longitudinal, transverse and diagonal cracks as one distress, code 63.
Causes in asphalt
PAVER gives three causes for these cracks in asphalt:
- A poorly built paving lane joint (longitudinal cracks only).
- Shrinkage of the asphalt surface because of low temperatures or hardening of the asphalt.
- A reflection crack from a crack under the surface course, including a crack in a concrete slab but not at a slab joint.
FAA AC 150/5380-6C says that oxidation and age hardening cause shrinkage. It says that thermal changes cause contraction. It adds that this type of cracking is not load associated.
A reflection crack over a joint in a concrete slab is a separate distress in PAVER (47). Movement of the slab, from thermal and moisture changes, causes it. Slab dimensions under the asphalt help to identify it. LTPP has a code for it (ACP 5), but its survey rules record it as longitudinal or transverse cracking.
Causes in concrete
In concrete slabs, repeated loads, curling stresses and shrinkage stresses usually cause cracks that divide a slab into two or three pieces. PAVER says that low severity cracks usually relate to warping or friction. It says that medium and high severity cracks are usually working cracks and major structural distresses. A hairline crack that is only a few feet long and does not cross the slab is a shrinkage crack. It is not a distress 63 crack.
Severity levels
The manuals do not use the same limits.
| Manual | Pavement | Low | Moderate | High |
|---|---|---|---|---|
| PAVER 48 | Asphalt, airfield | Mean width up to 6 mm, or filled, with no or minor spalling | Moderate spalling, or unsatisfactory filler, or width over 6 mm, or light random cracking near it | Severe spalling, with definite FOD potential |
| PAVER 63 | Concrete, airfield | Less than 3 mm | 3 mm to 25 mm | More than 25 mm, or severe spalling |
| LTPP ACP 6 | Asphalt, road | Mean width up to 6 mm | Over 6 mm and up to 19 mm | Over 19 mm |
| LTPP JCP 4 | Concrete, road | Less than 3 mm | 3 mm to under 6 mm, or spalling under 75 mm, or faulting up to 6 mm | 6 mm or more, or spalling or faulting at those limits |
FOD means foreign object debris. The PAVER limits in the table are for non-filled cracks and for non-reinforced concrete. Reinforced slabs have other limits. LTPP is a road program, so its limits are a reference and not an airfield rule.
How it is recorded
PAVER measures an asphalt crack in linear metres. If the severity changes along the crack, the inspector records each part on its own. The inspector does not record the crack in an area of block cracking. LTPP rates the whole crack at the highest severity that is present for at least 10 percent of its length. It does not record cracks shorter than 0.3 m.
Repair
AC 150/5380-6C says that simple crack filling may be the right repair for longitudinal and transverse cracks. Some cracks need partial or full depth repair.
Frequently Asked Questions
- What causes transverse cracks in asphalt?
- Two causes are common: shrinkage of the asphalt surface and reflection of cracks from a layer below. The shrinkage comes from low temperatures or from hardening of the asphalt with age. Reflected cracks come from cracks in the base or in concrete slabs under an overlay. These cracks are not usually load associated.
- How is the severity of a transverse crack rated?
- It depends on the manual. The PAVER manual for asphalt airfields rates a crack by spalling, filler condition and mean width, with 6 mm as the limit for low severity. The FHWA LTPP manual for roads rates asphalt cracks by mean width alone, with limits of 6 mm and 19 mm. For concrete, the limits are 3 mm and 6 mm.
- Is a transverse crack the same as a reflection crack?
- No. The direction of a crack gives the name transverse. The cause of a crack gives the name reflection. A reflection crack in an overlay can run in any direction. The PAVER manual lists reflection cracks over concrete joints as their own distress (47). It lists reflection cracks from other bases under longitudinal and transverse cracking (48).
- Does a transverse crack need repair?
- Not always. FAA AC 150/5380-6C says that simple crack filling may be the right repair for longitudinal and transverse cracks. Some cracks need partial or full depth repair. The choice depends on the crack and on the pavement.
References
- fhwa-ltpp-dim
- Distress Identification Manual for the Long-Term Pavement Performance Program (FHWA-HRT-13-092, revised May 2014) FHWA
- faa-paver-asphalt
- PAVER Distress Identification Manual, Asphalt Surfaced Airfields US Army Corps of Engineers (ERDC-CERL), attached to FAA AC 150/5380-7B
- faa-paver-concrete
- PAVER Distress Identification Manual, Concrete Surfaced Airfields US Army Corps of Engineers (ERDC-CERL), attached to FAA AC 150/5380-7B
- faa-ac-150-5380-6c
- AC 150/5380-6C, Guidelines and Procedures for Maintenance of Airport Pavements FAA
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