With billions of tax dollars being spent around the country on maintaining pavement infrastructure it is important to know how to spot a road in need of repair, before those repairs become critical and expensive. Some road rehabilitations are far cheaper than others and can help prolong a pavement segment’s lifespan while sensibly optimizing a city’s budget.
The most important things to recognize when doing a visual survey of a street are the types and quantities of pavement distresses that are present. The distresses measured can reflect the rehabilitation method that is best suited for each road segment. They can also provide a glimpse into the future condition of a roadway if it does not receive any rehab treatment. So, what are the different types of pavement distresses and how do they impact the overall lifespan and cost of rehabilitating a road?
For the purposes of pavement analysis certain types of distresses may have a more drastic effect on the overall pavement quality score.
Types of Pavement Distresses
There are several different pavement distresses that are identified by the ASTM (American Society for Testing and Materials). These are separated into two categories, Load Associated Distresses (LAD) and Non-Load Associated Distresses (NLAD).
Below is a collection of the eight most common distresses that may be present on asphalt streets:
Raveling – Raveling is the loss of fine aggregate materials on the pavement surface measured by the severity and number of square feet affected. This is an NLAD caused primarily by normal weathering. This distress is also commonly found in areas where there is heavy traffic around a turning area and the friction of tires can cause the surface materials of the road to come loose. Raveling reduces the friction of tires and increases roughness on the pavement surface. Raveling can spread very quickly.
Bleeding – Bleeding is the presence of free asphalt binder on the roadway surface caused by too much asphalt in the pavement or insufficient mixing of the aggregate materials. The result is a pavement surface with low skid resistance, especially when wet, and is measured by the amount and severity of the area. This is an NLAD that is commonly found in wheel paths.
Alligator Cracking – Alligator cracking or fatigue cracking is quantified by the severity of the failure and number of square feet. Even at low extents, this can have a large impact on the condition score as this distress represents a failure of the underlying base materials. It is one of the most common types of LAD and can spread rapidly if left unchecked.
Edge Cracking – Though edge cracking only appears on streets with unpaved shoulders, it can also be a sign of severe weakening of the pavement base. Edge cracking commonly occurs on rural roads without sufficient drainage. This allows water to seep under the surface of the street and begin eroding away at the base. Edge cracks may start forming from just outside the wheel path along the shoulder, but may spread very rapidly to the center of the street where much more damage will result in the form of alligator cracks and potholes. Drainage should be properly established so water cannot seep under the surface of the pavement.
Wheel Path Rutting – Starting at a minimum depth of ¼ inch, wheel path ruts are quantified by their depth and the number of square feet encountered. Like alligator cracking, low densities of rutting can have a large impact on the final condition score. This is a LAD that is caused by vehicle movement shifting the underlying pavement materials and is considered a pavement distortion.
Potholes – These are commonly seen in areas with lower structural standards and poor drainage where an already present distress, such as alligator cracking, have filled up with water enough that the soil beneath the pavement has begun to erode. Combine this erosion with continued pressure from street traffic and the surface asphalt is forced out of place. This creates a hole in the pavement where the asphalt surface is completely missing. Potholes are measured in severity from low at less than 25mm to high at over 50mm. Potholes can grow and become very dangerous if left unattended to. They can severely damage tires and vehicle suspensions, and even cause serious accidents. Potholes themselves are a NLAD but they are also usually a symptom of a much greater problem with the pavement base.
When assessing the overall condition of a roadway, taking notice of these common pavement distresses is key. Not only can these distresses help you to ascertain the remaining life in a roadway’s base, but they also reveal the types of rehabilitation treatment that may best suit a particular segment.
Here is a short list of the above distresses and their recommended rehabilitation treatments:
If you are interested in pavement management, check out our article on the Advantages of a Well-Maintained Pavement Infrastructure. Learn a few of the social, economic and quality-of-life benefits that come with good quality roads.