The Preservation Curve

High-tech materials, mobile equipment can keep potholed, cracked pavements in use longer.

By Tom Kuennen, Contributing Editor

Potholed, cracked or delaminated pavements are so common that they can be easily overlooked. That’s until driver complaints spur reaction, or until it becomes apparent that the pavement has decayed so much that it’s no longer worth remedial maintenance spending.

By that time, it will be no longer worthwhile to put any more money into the pavement to attain a serviceable condition. Having fallen off the “preservation curve,” during which maintenance funds will substantially extend the pavement’s service life, the pavement will have to be rebuilt at much greater expense than if periodic preservation had been provided (see adjoining page).

Classic “throw, roll and go” patching is a time-honored solution to pothole repairs.

Fortunately, a variety of pavement preservation tools exist – among them, new high-performance patch materials for asphalt and concrete pavements, and self-propelled pothole patching machines – that are making the preservation of potholed and distressed pavements, well, less distressful.

Pothole Patching Today

Historically, filling potholes might have needed a truck and a crew of maintenance workers, who would place a few tons of material per day. The “throw, roll and go” paradigm – in which workers toss shovels of hot- or cold-mix asphalt into a pothole, the rear tire of the truck backs over the pothole, and everyone moves on to the next pothole – no longer need be the norm. That’s because new methods automate this process with great improvements in productivity.

At the same time, the longevity and quality of pothole patch materials has gotten better. And with mobile patching equipment, even though more expensive equipment is required, agency work forces no longer are exposed to traffic in a moving work zone.

With higher cost materials, pothole patching should be considered an investment, rather than a quick fix. The material used should be selected on the basis of where a pavement fits into a pavement inventory and pavement management system (PMS). If a pavement is so far gone that it is ready for reconstruction, the least expensive material likely is the best for emergency repair.

By applying pavement maintenance at frequent intervals, existing pavement (green) condition can be prolonged over many years (blue), as opposed to letting the pavement decline over years to a point where major expenditures are required (red).

Ultimately, the issue boils down to available funds. The road industry and owners know how to build long-lasting roads, but they usually don’t have the funds to build the longest-lasting pavement. Instead, a road may not be constructed to optimal standards, and then the pavement may not be maintained in a timely manner that will prolong pavement performance. Potholes and other surface distresses can be the result.

The right choice of patching material should be determined after study, because pothole repairs should be an engineered process. Emergency repairs may use a material – such as hot- or cold-mix asphalt – that can hold for 48 hours to three months, perhaps until late spring. But other materials, when cured, can be far stronger than the existing pavement matrix, with the possibility that the pavement can disintegrate from around the patch, with the patch material still intact.

What is a Pothole?

The Federal Highway Administration defines a pothole as a bowl-shaped hole in the pavement surface, of various sizes, with a minimum width of 6 inches. Low-severity potholes are less than 1 inch deep, moderate from 1 to 2 inches deep, and high severity greater than 2 inches deep.