Time to Repair Potholes

Here’s how they form – and how to repair them

Mark the edges that will be sawcut or milled. Edges must be straight and research indicates a rectangular or polygon shape works best (as opposed to a square or rectangle).
Mark the edges that will be sawcut or milled. Edges must be straight and research indicates a rectangular or polygon shape works best (as opposed to a square or rectangle).

While the weather might not yet enable you to start all your pavement maintenance jobs, late winter/early spring is a great time to tackle the potholes that have popped up across many of the properties you handle.

Potholes start as cracks in the pavement. These cracks expand and contract with freeze/thaw cycles during the winter, and as cracks expand or become more prevalent, more and more moisture – rain and melting snow -- reaches beneath the pavement surface. This moisture weakens the base and subbase; as it loses its strength it can shift when traffic drives over it – and potholes can result.

This process is accelerated as the temperature drops because the wet material expands when it freezes, pushing up the pavement surface. The wet base or subbase contracts when the temperature rises and a thaw occurs.

After a number of freeze-thaw cycles, a small space is created between the asphalt pavement and the base. Traffic breaks the pavement into the depression, creating the beginnings of a pothole. The longer this pothole is left untreated, the deeper and larger the pothole becomes and the more extensive the damage to the surrounding pavement. Left untreated this defect will accelerate overall pavement deterioration. So it is cost-effective to repair potholes as soon as they occur.

While potholes are probably unavoidable it's important to realize that potholes can be minimized through proper pavement design, proper pavement construction and a regular maintenance program that involves crack repair, sealcoating, and timely overlays. Such a program can keep potholes to a minimum.

But when they do occur there are a variety of ways to repair potholes, depending on the goal and budget of the client.

  • Throw-and-go. This approach is the quickest, least costly (in the short term) and least-effective. It involves filling the pothole with cold mix asphalt until the mix sit above the surrounding surface, then compacting the cold mix. Compaction often is a hand tamper but often simply the pressure of a car tire driving back and forth over the repair.
  • High-performance mix. Available in bags or in bulk, these proprietary materials combine aggregate and emulsion specially formulated to adhere to itself and to the pavement and also to resist the effects of moisture. Some of the producers of this product design it to perform in specific climates so contactors can match the material to their climate. More expensive at first than cold mix asphalt, they are expected to last longer so the life-cycle costs of the material are generally lower.
  • Infrared Repair. While this is not a long-term option for some pothole problems, it can be used effectively to help prevent or delay potholes and it can be a relatively inexpensive quick fix that both repairs a pothole and make the pavement look good. With an infrared repair the pothole and the area surrounding it is heated by the infrared unit. As with any infrared repair it’s important that the heated area extend to a stable and sound pavement so the repair is tied to existing strength. Once the area is heated, rake the pavement and add asphalt mix to fill the pothole and spray rejuvenator on to the mix, then compact the heated area. Because infrared repair is basically a maintenance process it’s to the advantage of the property owner that it be used on cracked areas before they deteriorate to the point of a pothole (or near pothole).
  • Spray patching. A number of manufacturers make truck- and trailer-mounted and tow-behind units for spray patching. The process is similar on all equipment and involves air pressure blowing water and debris from a pothole, spraying a tack coat of binder on the insides and bottom of the hole, using high air pressure to blow asphalt and aggregate into the hole (the velocity compacts the material from the bottom up), and then covering the patched area with a layer of aggregate. Pavement can be opened to traffic immediately.
  • "Remove and replace." This approach takes longer, requires more labor and equipment and is more expensive. But it will generally yield better results and will last longer and will improve the overall pavement structure. That’s because remove-and-replace will get to the root of the problem – and then solve it. Here are the basic remove-and-replace steps:
    • Set up set up traffic control around the worksite. On parking lots and low-volume roads pay attention to traffic flow and pedestrian traffic and set up traffic control that guides people and traffic away from your work zone while protecting your crew. Contractors working on-road can consult the American Traffic Safety Services Association for traffic control guidelines. Workers also should wear appropriate high-visibility clothing.
    • Using either chalk or spray paint, mark the edges of the area to be removed. Edges must be straight and research indicates a rectangular or polygon shape works best (as opposed to a square or rectangle).
    • Make sure to extend the area to be removed into structurally sound, stable pavement. Don’t just remove the damaged area.
    • Remove the damaged pavement. Milling or sawcutting are best because they produce a clean edge for the repair. An air hammer can work but the edge it creates isn’t straight or clean and the action of the hammer can crack pavement that is structurally sound.
    • Excavate the area until you reach a stable grade. Make sure to remove all damaged or wet material of the base and subbase.
    • Replace base aggregate if necessary.
    • Apply a tack coat tot the vertical edges to improve adhesion.
    • Install asphalt in two lifts, compacting each lift separately.

Many contractors offer a variety of these options to their clients, to match the clients’ needs and budget. But the important thing to remember is that the primary cause of potholes is moisture. That’s why proper and timely maintenance of asphalt pavements – whether sealcoating or crack repair -- is required to protect pavement and extend its life.