Q&A: LRRB Pothole Repair Video
The LRRB, with assistance from Mn/DOT, has produced a new video, Pothole Repair: Proven Practices. Produced by Braun Intertec, the video offers up-to-date information on the best methods for handling those potholes that can't be avoided. Mike Marti of Koch Materials (formerly with Braun Intertec), who is also a member of the LRRB Research Implementation Committee, prepared this Q&A, which summarizes some of the major points covered in the video. The video will be available from Mn/DOT's Office of Research Services (http://www.dot.state.mn.us/inra.shtml) by late March; call 651-282-2272 for information on how to get a copy.
Year after year, our roadways have to withstand seasonal changes, extreme environments, and increasing traffic-both volumes and loadings. Yearly local government is faced with trying to maintain a vast network of roadways with decreasing budgets, to provide safe roadways for the public in a cost-effective manner. Since our cities, counties, and the state of Minnesota put millions of dollars into pothole patching every year, it's a good idea to look carefully at the advances recently made to the process of pothole patching.
Q: Who developed these advances?
A:Two research programs:
- Mn/DOT's Smooth Pavement Task Force
- FHWA Strategic Highway Research Program
In these projects, a combined total of more than one thousand potholes were repaired and then monitored to determine which repair methods work best. Both studies agreed that patches can last longer-and save us all a lot of money-if better materials and methods are used.
Q: What causes potholes?
A:
- Cracks develop in the pavement as a result of traffic, aging, and weather.
- Water from rain or melted snow gets into the cracks.
- When the temperature drops, the water freezes and expands, making the cracks deeper and wider.
- With more precipitation, more freeze-thaw cycles, and continued vehicle loading, sooner or later the cracks go all the way through the pavement. Now water can get underneath the surface.
- When this subsurface water freezes and expands, it pushes the pavement up and weakens it even more. When the ice melts and contracts, it leaves a space. So we have a weakened pavement layer over a cavity.
- With continued traffic and heavy loads-potholes!
Q: Are there different types of pothole patches?
A:Yes. They are classified as:
- Permanent
- Semi-permanent
- Temporary
In any given situation, three factors should be weighed carefully in deciding which patching method to use-pavement condition, pavement life expectancy, and the overall availability of resources. Following are some general guidelines.
Q: When is permanent patching used and what are the steps?
A:Permanent patching is the technique to use for a pavement that's in good condition, has a relatively long life expectancy, and when permanent patching fits into the agency's overall picture of available resources. Steps of permanent patching:
- Mark area to be patched. Keep area rectangular.
- Cut vertical edges (saw, jack hammer, or mill).
- Clean area (sweep and blow).
- Tack edges.
- Place, do not throw, high-quality patch material.
- Compact the material!!!
Q: What is the difference between permanent and semi-permanent patching?
A: Semi-permanent patching is used as a proactive measure to keep a small pothole from turning into a major failure. The procedure for semi-permanent patching is similar to permanent patching. The difference is that you don't cut the pavement.
Q: When is temporary patching used?
A: It's the right choice when there is a hole that could damage vehicles and needs to be patched right away-but it is not realistic to close the road. Temporary patching is also used for a road that's in generally poor condition or is scheduled for an overlay or reconstruction.
Q: How can temporary patches be improved?
A: Research emphasizes that some simple changes in the temporary patching process can produce higher quality, longer lasting patches. As with permanent and semi-permanent patching, materials and methods make a difference. And the message here is the same as before: The most cost-effective repairs are made with high-quality material.
Most important, the well-known "throw and go" technique should be discontinued-and replaced with a "place-and-roll" method. In other words, place the material in the hole instead of throwing it in. And be sure the material is in the hole-not around the hole. Again, compaction was found to be very important. Researchers state that, for temporary patches, good results can be achieved by driving, or rolling, over the patch several times. For better results, compact more carefully with a tamper or vibratory compactor.
Q: What are the three most important things to remember?
A:
- Use high-quality patching material. It is cost-effective compared with using less expensive material, which ends up costing more in the long run because it doesn't last.
- Compaction is essential for every patch-even if it's just driving over a temporary patch with a truck.
- The old "throw and go" method for temporary patching should be replaced by a "place and roll" method.