What are these distresses on my pavement?
Cracking, deformations, and deterioration are three categories of pavement distresses. Each of these distresses can indicate how well your pavement is performing, or more critically, how much longer it might last. Identifying the distresses on your asphalt pavement can help you formulate the most cost-effective maintenance plan.
Cracking
This is the most recognizable form of pavement distresses. Cracking can occur for a number of reasons, but the main causes are either environmental factors or inadequate pavement structure. Environmental factors that cause cracking are temperature and UV radiation from the sun. Harsh Minnesota winters bring very cold temperatures. These cold temperatures cause the pavement to contract and try to pull away from itself (i.e., crack). While the asphalt is new and fresh, it is flexible and can stretch, but the aging of the asphalt caused by UV radiation (called oxidation) makes the asphalt more brittle with each year until it can no longer resist the cold temperature shrinkage. This process produces thermal cracks that are very consistent, evenly spaced cracks that typically travel in the same direction. Sealcoating creates a protective layer on the surface of the pavement that can slow the aging process or consider using a specialty crack-resistant asphalt binder next time you rehabilitate your pavement.
Other cracks can also be caused by the aging (or oxidation) of the asphalt surface, but instead of cold temperatures, traffic loads can cause the more brittle pavement to crack. Over time, the cracks interconnect and form what is called block cracking, due to the checkerboard-like pattern created by the cracks. Pavements with block cracking are usually well built and can be easily maintained with cracksealing and sealcoats, and they are great candidates for rehabilitation with a mill and overlay.
Structural cracks are a different type of crack. These cracks start at the bottom of the pavement and may take a few years to appear. Structural cracks are caused by weak subgrades and/or asphalt pavements that are too thin, which allows heavy traffic loads to flex the pavement beyond what it can resist. These cracks are called fatigue cracks, or more commonly called alligator cracks because the crack pattern resembles alligator scales. Fatigue cracking can occur in isolated areas of a properly designed pavement or can be widespread if the pavement is under designed.
Deformations
Pavement deformations are caused by subgrade failures, asphalt deformations, and/or freeze-thaw cycles. All of these deformations can look very similar but are caused by very different issues. When the subgrade, the material below the asphalt pavement and aggregate base, is too soft, it can be compressed by the traffic loading on the surface to create a depression in the pavement. Subgrade failure deformations typically affect larger areas and look like the pavement has settled or sagged to create a wide bowl for water to pool. Asphalt mixtures can also have deformation issues. There are many known factors that can contribute to these deformation issues, including the binder grade, the angularity of the aggregates used, the amount of fine aggregate in the mix, the number of binder in the mix, the amount of recycled materials in the mix, and more. Asphalt deformations are typically small and look as if the asphalt moved straight down where the heavy load was applied and bulged up slightly around the applied load.
Generally, these deformations occur early in the pavements life, and depending on the severity, can be corrected with mill patching, full depth patching, or rehabilitation of the pavement.
Additionally, deformations can be formed during winter’s freeze-thaw cycles, which can cause ice lenses to form below the pavement. These ice lenses cause the pavement to heave upward when formed and after the ice lens melts, the area becomes a depression in the pavement. For more information on freeze-thaw cycles see our blog from February.
Deterioration
The last form of pavement distresses is deterioration, or the loss of pavement materials. Raveling is one form of deterioration and is the progressive loss of asphalt materials from the surface of the pavement. It starts with the fine aggregates breaking loose, which exposes the larger aggregates. Eventually, the larger aggregates may begin to break loose, creating a rough driving surface and pockets for water to infiltrate the pavement. Pavements that are showing signs of raveling should be seal coated to protect the pavement surface from further deterioration.
The most common and most recognizable form of deterioration is potholes. Potholes form when large chunks of pavement are broken loose or deteriorated to rubble and carried away. Potholes form in areas already affected by cracking and deformation and should be repaired quickly to avoid damage to vehicles or injury to pedestrians.
Download our Pavement Distresses Flyer to identify the distresses affecting your parking lot, or contact BR to have a pavement assessment performed by one of our trained professionals.
Bituminous Roadways, Inc. is the Twin Cities’ most respected and sought-after asphalt pavement company. With more than 70 years in the industry, we provide dependable service and the highest level of quality asphalt paving anywhere. We proudly serve the Twin Cities metro and the surrounding area.