Pavement Preservation Journal, Spring 2015, Vol. 8, No. 1
By Larry Galehouse, P.E., P.S.
Every spring the news media embark on their pursuit of potholes and the damage they cause to vehicles. In some locations it has been become an annual ritual to embarrass road agencies for their lack of proper maintenance. In response, road managers often counter that a lack of sufficient road funding is responsible for poor pavement conditions and the resulting potholes.
Although both sides of the discussion have merit, because of potholes, road users must endure repair costs and inconvenience. Drivers experience damage to tires, wheels, and vehicle suspensions.
Sometimes serious road accidents occur as a direct result of potholes on high speed roadways. Motoring and related organizations estimate that potholes cause billions of dollars in damages to vehicles in the United States each year. But it doesn’t have to be that way, because simple practices exist can that effectively thwart the development of potholes.
POTHOLES IN WARM, COLD CLIMES
Most people know that potholes are caused by the presence of water in the underlying pavement structure. Both warm and cold climate regions suffer potholes.
In warm climates, erosion by water present in the road’s structure undermines a road’s driving or friction course. Combined with the presence of traffic, the affected driving course begins to weaken, then suffers fatigue, and ultimately the poorly supported driving course is broken, creating a hole in the pavement surface. Now even more water can enter the pavement structure.
In cold regions, cycles of freezing and thawing accelerate this process as water infiltrating within the structure freezes and exerts pressure on the pavement above. When the road and trapped water thaws, the resulting cavity collapses under traffic, forming a pothole. Sometimes water from the thawing of upper portions of the pavement structure cannot drain past still-frozen layers below. The saturated supporting pavement structure is weakened and the pothole forms.
How does water get into the underlying pavement structure and create a pothole in the first place?
The simple answer is that almost always, the cracks and joints are left unmaintained and unsealed.
The time to solve the pothole problem is when the cracks begin to form on the pavement surface. Yet many road agencies forego easy and low-cost crack treatments in lieu of more costly pothole repair.
Pothole repair is full of risk for the driver, maintenance worker, and highway agency. Although some road agencies use sovereign immunity as a defense, there is no defense for a loss of life.
Maintenance workers who fill potholes are unprotected by work zones and exposed to traffic, often resulting in fatalities. Moving pothole filling operations – the “throw, roll and go” method in which staff forces shovel asphalt mix into a pothole, the rear tires of the haul truck are backed over the hole, and the operation moves down the road – often are inadequately marked, with drivers suddenly coming on an operation with little warning.
But crack and joint sealing usually are performed in a proper work zone, reducing the risk for workers and drivers.
DO IT RIGHT FIRST TIME
Maybe you have heard the saying, “there is never enough time and money to do it right the first time, but there is always enough time and money to do it over”.
In this instance, doing it right the first time means implementing a crack and joint sealing program in advance, while doing it over (and over) is the practice of pothole filling and patching, that is, waiting until the fix becomes dangerous and more expensive.
The following simple steps, done in advance, will prevent potholes from forming:
• Begin by sealing small cracks in flexible pavements early in the pavement life when it is in good condition, and continue sealing throughout the pavement life. Transverse, longitudinal, reflective, block, and edge cracks should all be sealed. When the pavement is properly sealed, potholes and parallel crack development are very rare
• Monitor concrete pavement joints and reseal if there is a loss of sealant, or an adhesion or cohesion failure
• Seal the interface between the pavement and all castings, e.g., manholes, catch basins, water valves, etc., and
• Seal the joint between the pavement and the concrete (curb) gutter pan.
Keeping water out of your pavements by keeping cracks and joints filled or sealed during the summer will go a long way in avoiding potholes the next spring.
A video defining the problem is available at: http://youtu.be/j9lAgMT
Technical information on crack and joint treatments may be found at: https://www.pavementpreservation.org
Galehouse is executive director, National Center for Pavement Preservation at Michigan State University
