How to Spot A Failing Asphalt Street
Those in charge of making decisions about maintenance and rehabilitation of roadways understand the best way to stretch our budget dollars is by programming M&R work projects early in the life of the road before those repairs become critical and expensive. Many road rehabilitation activities can help prolong a pavement segment’s lifespan while sensibly optimizing a city’s budget.
One of the most effective ways to avoid more costly road maintenance is to have a plan in place for constant monitoring of roadway conditions. Ideally, a system-wide pavement condition survey occurs periodically, at least once every three years. This survey data is commonly loaded into a robust software program that is used to create maintenance and rehabilitation work programs that can be adapted to regional best practices and costs and customized to fit budgeted dollars.
So let’s discuss the pavement condition survey process. What are we looking for? The most important things to recognize when doing a visual survey of a street are the types, and quantities of pavement distresses present. The distresses measured and quantities of each can reflect the rehabilitation method that is best suited for each road segment. Some types of distress impact the pavement quality score more than others. They can also provide a glimpse into the future condition of a roadway if it does not receive any rehab treatment.
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 and is 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. Untreated raveling can cause pavements to deteriorate 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 and at intersections.
Patching – Patching is an area of the road that has been replaced by new material to repair the existing pavement. A patch is always considered a defect no matter how effective it is. When the majority of a roadway surface is covered by a patch, such as a large utility replacement, the rating of the patch is minimized and the patch it is considered a NLAD. When a patch is used to cover a defect such as alligator or edge cracking it indicates pavement failure that needs short-term attention.
Longitudinal Cracks – These are quantified by their length and width. These distresses are primarily due to age and weathering and not considered a LAD. Longitudinal and Transverse cracks that intertwine can indicate the start of alligator cracking. These cracks are common on all roads and can result in moisture entering and weakening the roadway base. Whenever possible they should be waterproof-sealed to slow damage to the surface around the cracks and keep water away from soils under the pavement.
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 pavement 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 maintained or re-established so water cannot seep under the edge/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 pavement condition score. This is a LAD can be caused by repeated heavy vehicle traffic, inadequate asphalt mix design, and vehicle movement shifting the underlying pavement materials and is considered a pavement distortion.
Potholes – These are commonly seen in areas with aging pavements and poor drainage where already present distresses, such as alligator cracking, have filled up with water enough that the wet soil beneath the pavement loses its ability to support the asphalt or concrete above. 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 understanding 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:
- Raveling – May be slowed by the application of surface maintenance treatment such as chip seal or micro-slurry seals or thin asphalt overlays.
- Bleeding – Though minor bleeding can be addressed through the light application of coarse sand (to absorb the excess asphalt binder) major bleeding is often addressed with surface rehabilitation or reconstruction.
- Patching – Though patching is already considered a pavement rehabilitation, it is still important to monitor the patching process to assure quality mending of the existing roadway. Edges of patching should be waterproof sealed to keep water out.
- Longitudinal and transverse cracks – Deterioration of cracks of this type can be slowed through a waterproof sealing process. In the case that the cracking is severe or wide, localized patching may be needed. It is very important that longitudinal and transverse cracks be treated before and as part of the rehabilitation of roadways. (ie; crack seal before an overlay).
- Alligator cracking – for this type of distress, sealing is generally not going to be effective. If the cracking is small and localized it may be dug out, carefully cleaned, and replace with a patch. A large section of alligator cracking is a common first sign of pavement structural failure and often indicates that the base and sub-base under the roadway should be examined and rehabbed as needed.
- Edge cracking – This type of cracking spreads very quickly so even light edge cracking should be waterproof sealed as early as possible. Drainage should be properly maintained or re-established so water cannot seep under the edge/surface of the pavement.
- Rutting – Heavy rutting (>1/3 inches deep) can be a significant concern on higher-speed road segments because of the possibility that vehicles could hydroplane during rainstorms. Milling of the road surface should occur where rutting exists prior to asphalt overlays.
- Potholes – These can get substantially worse over time and present a major danger to motorists so, they must be repaired by patching or at a minimum, filling as early as possible.
If you have any needs related to pavement management or evaluation of your pavements, IMS can help.
We have completed over 1,000 pavement management projects and rights-of-way asset management assignments across the United States. Contact us for more information.