Understanding Pavement Defects

Losing Your Car to An Asphalt Pothole

 

Defects in Asphalt That Every Property Owner Should Know-Part 1

    

 

From time to time every parking lot and roadway will experience some type of defect or failure. From the stress of vehicle traffic to the impact of weather all asphalt has a life cycle. It is important for the property owner to not only identify the type of asphalt failure their surface is experiencing but to also choose the best repair technique. Here is the introduction to pavement defects.

Alligator Crack
Alligator Cracking

Alligator cracking is a load associated structural failure. The failure can be due to weakness in the surface, base or sub grade; a surface or base that is too thin; poor drainage or the combination of all three. It often starts in the wheel path as longitudinal cracking and ends up as alligator cracking after severe distress.

FIX: Because a structural failure is taking place the only possible solution to alligatoring is to perform a full-depth patch.


Block Cracking 

Block cracks look like large interconnected rectangles (roughly). Block cracking is not load-associated, but generally caused by shrinkage of the asphalt pavement due to an inability of asphalt binder to expand and contract with temperature cycles. This can be because the mix was mixed and placed too dry; Fine aggregate mix with low penetration asphalt & absorptive aggregates; poor choice of asphalt binder in the mix design; or aging dried out asphalt.

FIX: Less severe cracks measuring 1/2 inch or less can be sealed to prevent moisture from entering into the sub grade. More severe cracks should be fixed by removing the cracked pavement layer and replacing it with an overlay.

 

Raveling
Raveling (very porous asphalt)

Raveling is the on-going separation of aggregate particles in a pavement from the surface downward or from the edges inward. Usually, the fine aggregate wears away first and then leaves little "pock marks" on the pavement surface. As the erosion continues, larger and larger particles are broken free and the pavement soon has the rough and jagged appearance typical of surface erosion. 

There are many reasons why raveling can occur, but one common cause is placing asphalt too late in the season. This is because the mixture usually lacks warm weather traffic which reduces pavement surface voids, further densification, and kneading of the asphalt mat. For this reason raveling is more common in the more northern regions(snow belt).

FIX: Apply a thin hot-mix overlay. Other solutions could include: sand seal, chip seal, slurry seal or micro-surfacing. 


Other issues that need treatment before maintenance:

Oil Spots - oil spots are a common problem in parking lots and driveways. These areas must be treated before sealcoating or the oil and chemicals will seep up through the newly applied material and render your sealed surface ineffective. There are number of great products for treating these types of issues. Ask your material supplier what they offer.

Grass - Poorly maintained parking lots will often have grass growing up through the cracks. Cleaning the cracks should be standard practice before sealing them. Use a heat lance to burn out the crack and/or blow out the cracks depending on the severity of the problem.

Mud, tree sap, berry stains, etc - Anything that would sit between the asphalt and the sealer must be removed. Without removing it the sealer can not properly adhere to the asphalt and will eventually (sooner than later most likely) peel off. Blowers, push brooms, pressure washers, and gas powered brooms are all tools you should have in your pavement maintenance arsenal.