Asphalt rutting remains one of the leading forms of flexible pavement distress and is classified as a longitudinal surface depression located along the wheelpath. There is no exact severity levels defined for this type of distress, instead measurements of surface depressions are used for analysis. These measurements are then classified as low, moderate and severe, and reflect which repair methods are applied.
Rutting occurs in the wheel path as a permanent deformation impacting any pavement layers or subgrades. Consolidation or lateral movement of materials usually leads to rutting. Rutting shows up in wheel paths because traffic loads apply the most pressure here leading to reoccurring stress.
Rutting Measurement: Identifying Severity
The average rut depth in the wheel path of a given segment or sample measures severity of rutting.
Low Severity = ¼ inch to ½ inch
Medium Severity = ½ inch to ¾ inch
High Severity = anything over ¾ of an inch
The extent of rutting is the full length of the segment in the wheel path. Measurements should be taken from as many locations as possible and then averaged out.
If rutting becomes extreme the surrounding pavement layers can become raised. In most cases, rutting forms progressively right along the wheel path, and eventually reaches a maximum depth at the center of the path. These ruts are most notable post-rain because they fill up with water. Wear is another key term associated with rutting that refers to the surface depression of the wheel path, caused by tire abrasion.
Types Of Rutting
There are two types of rutting: mix rutting and subgrade rutting.
Mix rutting results when the subgrade does not rut but the pavement surface shows depression marks in the wheel path as a result of compaction and/or mix design problems.
Subgrade rutting is classified by the subgrade showing depression marks along the wheelpath as a direct result of loading. As a result, the pavement settles into the subgrade ruts creating a sunken appearance in the wheelpath.
What Causes Asphalt Rutting?
Continuous traffic load can cause any asphalt to show signs of rutting due to consolidation or lateral movement of materials. Certain circumstances as well as improperly mixed or applied asphalt make roadways more susceptible to rutting. Some common causes of asphalt rutting include:
-Improper compaction of HMA layers in the construction process may cause pavement to continually become denser when placed under the pressure of traffic loads. This is why proper construction techniques with adequate compaction remain fundamental to quality asphalt.
-A number of issues relating to the mix design or manufacture, such as excessive mineral filler, too high asphalt content or insufficient angular aggregate particles in the mix.
-The actual wearing away of surface particles due to consistent traffic.
-Inadequate pavement structure leading to subgrade rutting.
-Plastic deformation is when the material fails and the mix becomes displaced and tends to hump up along the outside of the wheel path. This occurs because the mix does not have the strength needed to hold up under constant stress imposed by loaded vehicle tires.
-In cold climates where it snows ruts are more likely to form due to studded snow tires. While damage remains the same, it is related to mechanical dislodging caused by wear and tear as opposed to pavement deformation.
Repairing Asphalt Rutting
There are special challenges and considerations to keep in mind when fixing asphalt rutting based upon the cause of the damage as well as the extent of rutting. An investigation must take place in order to determine the cause of failure. Investigations may include a visual inspection or more extensive sampling and testing, such as trenching.
If damages are related to structural deficiencies, the pavement may not be a good candidate for preventive maintenance treatment. Faulty construction is typically best fixed through reconstruction or rehabilitation. Maintenance treatments are less severe but only effective if the issue is related to normal wear and tear caused to properly constructed asphalt.
If damages are related to plastic deformation all of the damaged materials are removed and replaced with a mixture that can adequately hold up under given stress and temperature conditions.
If pavement is deeply rutted the cause must be determined prior to repairs in order to ensure it doesn’t occur all over again. Low severity ruts (under ½-inch) can generally be left alone unless they show signs of worsening. When dealing with pavement that is heavily rutted a successful project typically entails leveling and overlaying the pavement.
Kleenco Construction knows the industry inside and out, repairing asphalt rutting comes second nature to us. We provide solutions to anything and everything that comes our way, hence why we are trusted to handle some of the largest projects in the industry.