Why Does My Parking Lot Have Potholes? And What Can I Do to Prevent Them?
Your asphalt pavement is designed to last more than 15 years with timely, proper maintenance. Potholes can occur when that maintenance has been ignored or when maintenance procedures have been delayed or performed poorly.
Potholes occur when the supporting material beneath the asphalt pavement surface has been weakened. That means the aggregate base is probably wet and, if the damage is severe enough, the subbase (dirt or clay) beneath the aggregate is wet also. Simply put, water weakens.
As asphalt pavement ages it oxidizes and becomes more brittle; this is normal. As with any material that is brittle, it can begin to crack; this is normal too. These cracks start out small but if left untreated will grow longer and will widen. Climate and traffic can speed cracking, and cracks will expand during the winter.
If you neglect the cracks in your pavement you eventually will begin to see potholes…because here is how to make a pothole:
First, the pavement becomes damaged. This can be the result of some unusual trauma – a car accident, for example, where a light pole falls and gouges the pavement – but it is usually the result of age. As explained above this can be accelerated by poor or improper maintenance, but the result is that the damage creates pathways for moisture to work its way beneath the pavement surface.
Once the moisture is beneath the surface it weakens the base and subbase because that’s what water does. Then, if you live in the right climate, it will freeze. And as we all learned in Junior High by filling and freezing a glass jar with water, water expands when it freezes. In Junior High the water cracked the glass, but as water freezes and expands beneath the pavement it basically pushes the pavement surface up, a little.
As temperatures rise, the frozen aggregate and subbase warm and contract. What do they leave behind? A small space beneath the asphalt surface. This means that a small area of asphalt pavement is no longer supported by the base and subbase.
In many areas of the country where the temperature fluctuates above and below freezing this can happen many times over the course of a winter. These are termed “freeze-that cycles.” Each time the temperature rises not only does the pavement’s support system contract but there’s another opportunity for more moisture to find its way beneath the pavement. When the temperatures drop and the base and subbase freeze again, they expand and push the pavement up even more (and even more again if there’s more moisture to work with). Then when temperatures rise again the pavement’s support system contracts again, leaving behind an even larger space beneath the asphalt surface. You can see where this is headed. It’s easy to understand the havoc that numerous freeze-thaw cycles can wreak on a damaged pavement.
But that’s only opening the door to the real problem. Eventually the weakened pavement surface collapses into the small space beneath it. This can be caused by traffic or, if the pavement is weak enough, it can just happen on its own. Now you have the very small beginnings of a pothole.
But, and this is important, now with the collapsed pavement you have an even bigger opening for moisture to seep beneath the surface! So the process not only continues, it is exacerbated and happens progressively faster. The small crack that was left unattended has created a small pothole, which, if left unattended, will create a bigger, more costly and unsafe pothole.
And this pothole problem is contagious. Water finds its way, so once it’s found a way beneath the pavement surface it continues to move. As it moves down it further weakens the structure directly beneath the small pothole. As it moves horizontally it extends the weakness of the pavement structure across a broader area. This can create more potholes but is often likely to create extensive “chicken-wire” or “alligator” cracking (so called because it looks like chicken wire or alligator skin). If your pavement gets to this point you have a major job ahead of you that could be both complex and costly.
While it is impossible to prevent all potholes – the brutality of winter combined with traffic and aging asphalt virtually guarantees your pavement will experience damage – you can delay their development, you can restrict their growth, and you can repair them ASAP.
Here’s what you need to do to prevent potholes and the surrounding damage.
1. Remove and replace damaged areas
If you already have potholes or if any areas exhibit chicken-wire cracking, those areas probably need to be removed and reconstructed. (Ask your contractor.) That process involves saw-cutting around the damaged area, removing all damp or weakened substructure and replacing it with new material, then constructing an asphalt concrete surface patch to protect the new support structure. Failure to take this step will certainly lead to much more extensive and much more costly repairs in the too-near future.
2. Repair cracks
Cracks are the easiest way for water to find its way beneath the surface so it’s essential to fill them. Basically cracks ¼-inch wide or wider need to be filled. They can be filled using an unheated cold-pour material, but in most cases a hot-applied, rubberized material provides better protection and lasts longer. Cracks need to be clean and free of grass and other debris, and their sides need to be sound to accept the material.
3. Sealcoat your pavement regularly
This is the easiest, most cost-effective maintenance approach to protect your asphalt pavement investment and to delay deterioration.