What Is Rutting In Pavement?
What Is Rutting In Pavement?
A rut is a depression or groove that forms in the surface of a flexible pavement as a result of repeated vehicle traffic.
It is found in the wheel tracks of the roadway and can become deeper over time as vehicles continue to pass over it.
The depression may also be accompanied by an upward bulge or heave on either side of the rut as the pavement becomes worn and damaged.
Rutting is a type of damage that occurs on asphalt roads over time due to the accumulation of permanent deformation or consolidation. It is characterized by the appearance of grooves or indentations in the road surface, typically in the wheel paths.
Asphalt is a flexible material, and rutting can be more pronounced in hot weather when the binder on the surface of the road becomes sticky.
The cause of rutting is the movement of the aggregate and binder in the asphalt, similar to how a wagon might leave tracks in dirt. It is not caused directly by the weight or movement of vehicles on the road.
What Causes Rutting In Pavement?
There are three primary causes of rutting in flexible pavements:
- Asphalt Layer Problems
If the mix-design of the asphalt is not suitable or the layers are not adequately compacted, it can lead to unacceptable surface rutting. On the other hand, a proper mix-design should be able to support traffic for the entire intended lifespan.
The asphalt layers must be firm enough to resist deformation and outward flow under the weight of tires, but also flexible enough to prevent fatigue cracking. The mix-design must be able to handle the expected traffic loads, volume, and climate conditions.
Factors that affect the stiffness of the mix include the size and shape of the aggregate particles, the proportions of different sizes in the mix, and the grade and type of bitumen used to bind the aggregate.
The asphalt mix must also have the proper proportions of aggregate, binder, and voids for the specific mix type.
Poor compaction can cause the asphalt layers to compress under the weight of traffic, resulting in surface rutting, but this is generally not an issue with modern materials, equipment, and techniques.
However, problems can occur if the asphalt cools below the optimal temperature before compaction is finished, for example, if it has to be transported a long distance to the job site.
- Structural Layer Problems
The subbase and base layers of a pavement are responsible for supporting the weight of traffic. If these structural layers are too thin, the load on the foundation of the pavement may be too great, leading to deformations on the surface, such as rutting.
However, including Tensar geogrid in the base layer can increase its strength and stability, reducing movement of the aggregate particles and helping to distribute and reduce the load on the foundation. This can extend the lifespan of the pavement and lower maintenance costs.
- Weak subgrade layer problems
The pavement design relies heavily on the strength of the subgrade. If the subgrade is weaker than expected, the pavement may be more prone to rutting.
This can be caused by moisture entering through cracks in the pavement, poor drainage, or construction activities that weaken the subgrade.
These issues can be addressed through maintenance, timely repairs, and resurfacing as needed.
In some cases, the subgrade may be weaker than expected due to unexpected soil conditions, insufficient site investigation prior to construction, or faulty testing or interpretation of test results.
Using a product called Tensar geogrid can help stabilize the subbase and prevent rutting during construction by increasing the subbase’s bearing capacity and resistance to rutting.
What Problems Are Caused By Rutting?
Rutting can be a safety concern as it can affect steering and increase the risk of aquaplaning. It can also lead to driver discomfort and potential hazards due to maneuvering to avoid ruts.
Additionally, rutting can decrease the lifespan of a road by causing surface cracking and weakening the pavement, leading to increased maintenance requirements and shortened service life.
What Are The Types Of Rutting?
Rutting is an unavoidable symptom of road use, and it’s important to understand the different types of rutting in order to evaluate the condition of your pavement.
Rutting can be divided into two main categories: surface rutting, which is caused by traffic loading on flexible pavements such as asphalt; and sub-surface rutting, which occurs when the roadway subgrade fails due to consolidation or insufficient stabilization.
Surface rutting typically appears as shallow grooves on the pavement surface, while sub-surface rutting typically manifests itself as deeper ruts that can cause instability or reduced drainage capacity.
Understanding these different types of rutting allows for proactive maintenance and repair strategies that will save money in the long run.
