Types of road cracks and how to avoid them

by Michal Golos, on 22-Apr-2021 04:20:10

Over time, roads can develop cracks due to distress from traffic and the climate they are subjected to. The type of road, as well as the type of distress will have an impact on the type of road cracks that can appear.
In this guide, we’ll discuss the different types of road crack, what causes road cracking, and how it can be avoided. Read on to learn more about:

What are the different types of road cracks

The FHWA Distress Identification Manual identifies seven different types of road cracks:

  • Fatigue (alligator) cracking
  • Block cracking
  • Edge cracking
  • Wheelpath Longitudinal cracking
  • Non-Wheelpath Longitudinal cracking
  • Transverse cracking
  • Reflection cracking

Fatigue (alligator) cracking

Fatigue (alligator) cracking starts as a series of interconnected road cracks that develop to break the road surface into multiple, irregular shaped pieces, usually less than 500mm in size. Repeated loading causes incremental damage that manifests a micro crack initiating predominantly from the bottom of the asphalt layer. The crack grows, until it extends through the full asphalt layer thickness. These road cracks are often referred to as alligator cracking.

Moderate Alligator Cracking in Wheelpath
Moderate alligator cracking in wheelpath

Saughtree Station - Severe Alligator Craacking
Severe alligator cracking

Block road cracks

Block cracking is a pattern that occurs as a series of roughly rectangular blocks, ranging from 0.3m to 3m in size.

Beech Road - Severe Bloack Cracking
Severe block cracking

Edge road cracks

Edge cracking is long cracking in the outer 0.3 to 0.6m of a pavement that curves to the pavement edge.

Stone Road, Dereham - Edge Cracking
Edge cracking

Wheelpath Longitudinal road cracks

Wheelpath Longitudinal cracking runs parallel to the pavement's centreline, caused by fatigue.

Non-Wheelpath Longitudinal road cracks

Non-Wheelpath Longitudinal cracking is randomly located but still parallel to the centreline. They are predominately created between the existing pavement and new widening, but may also be a result of expansive clay subgrade soils. 

Libya - Longitudinal Cracking
Longitudinal cracking

Transverse cracking

Transverse cracking describes road cracks that are aligned across the carriageway perpendicular to the centreline. This type of cracking can be thermally induced or due to underlying joints or cracks.

Transverse Cracking A14 Rougham to Rougham Nurseries SUfflok
Transverse cracking

Reflection road cracks

Reflection cracking describes cracking in asphalt overlay located in concrete pavements, or over shrinkage cracks in cement treated base layers. It occurs over an existing crack in the underlying surface. This causes stress concentration in the asphalt layer that eventually leads to the initiation of a crack that extends up to the surface.

Reflective Cracking Over Joints in Concrete Substrate_Generic Picl-1
Severe transverse reflection cracking over joints in concrete substrate
(Photo courtesy of Pavement Interactive)

What are the causes of road cracks?

Load induced road cracks

Load induced cracking is caused by repeated loading from traffic: either fatigue cracking or reflection cracking as detailed above.

Non-load induced road cracks

Non-load induced cracking is generally thermally induced and is referred to as low temperature cracking. This describes the road shrinking at lower temperatures, generating tensile stresses in the asphalt, which lead to transverse (across the road width) cracking. Another form of non-load induced cracking is associated with the presence of expansive clay subgrade soils. If these soils dry out, they shrink, causing longitudinal (along the road) cracking in the road surface.

How can road cracks be avoided?

Tensar has a range of solutions to help prevent several types of road cracks including fatigue, reflective, and longitudinal cracking and extend your asphalt’s lifespan.

Fatigue cracking results from repeated flexing of the asphalt pavement. The degree of flexure is dependent upon the structural strength of the pavement. Tensar stabilisation geogrids incorporated into the subbase or unbound base layer of a pavement increase the strength of the pavement, reducing deformations and fatigue in the surfacing.   The fatigue resistance of an asphalt overlay can be improved by the inclusion of Tensar AX5-GN structural interlayer at the base of the overlay.

Reflective cracking in overlays can be delayed by inclusion of an appropriate asphalt interlayer. Tensar has a range of asphalt interlayer products that have been proven to reduce reflective crack propagation.

Longitudinal cracking due to the presence of expansive clay soil can be prevented by a Tensar stabilisation geogrid in the unbound granular layers, to control lateral movement of the unbound layers in the event of clay shrinkage.

For more information, visit our Tensar solutions.