In one capacity or another, Mike Kennedy has been working for nearly three decades in Minneapolis’ streets department, which is charged with patching the city’s potholes. (Kennedy, now the city’s director of transportation, maintenance and repair, said he does not resent R.T. Rybak for stealing the title of his memoir.)
We always seem to have some level of a “pothole bloom” when the temperatures warm up in the spring. Every year I seem to get the same question, “Is this the worst pothole year you’ve ever seen?”
The enemy is water. Over the winter, moisture gets down into the pavement through joints and cracks and infiltrates the pavement. Older streets have plenty of crevices and other paths for water to seep into. As water freezes, it expands. It pushes the pavement materials apart and pushes up on the pavement’s surface. When the ice melts, it contracts and the surface can cave in. That’s a pothole.
As traffic pounds down on the roadway, the material breaks up further and the pothole can grow larger. If there is water present, the materials get splashed out, causing the pothole to grow wider and deeper. You get all sorts of sizes — from a surface defect to a full-blown pothole that reaches down into the subgrade. They can sometimes grow as big as 3 feet wide and upwards of 10 inches deep.
Pothole repair is typically reactive, meaning we wait until they form to fix them. We don’t track potholes, we don’t try to count them. We do the worst first, looking for anything that’s going to damage a vehicle. We generally start on the streets with higher traffic and faster speeds.
The same people who plow the streets fix the potholes. In the late winter or early spring, we may have to spread our resources between plowing snow, opening storm drains to prevent flooding, and filling potholes – all at the same time! On a typical early spring day before we start our permanent patching season, we may have two to five crews of two to four people each. Some are just working out of a pickup truck with asphalt while others have specialty trucks or a trailer that can keep the asphalt hot for better workability. At that time of year, we’re trying to fill as many as we can and cover as much ground as we can. It’s about shoveling the patching in, maybe packing it down a little bit. Then off you go.
The winter repairs are made with a cold mix, also known as a street mix, which is a cold asphalt that doesn’t bond or stay very well at all. But you can use it in the colder temperatures. Sometimes it lasts into the summer, sometimes it lasts for a week and sometimes it lasts for less than a day. We often have to go back around and patch the same potholes repeatedly.
In the winter, it’s about temporary patching, but in the summer we can perform permanent repairs. The difference is that we can use better materials and procedures. First the pothole gets cleaned out, then the sides and edges are coated with liquid asphalt cement, which is the black material that’s mixed with gravel to make asphalt. This acts like a glue for the hot asphalt, which is placed in the hole, rolled and compacted. It cures quickly as it cools to make a durable and long-lasting repair. The upside of permanent repairs is that they last, but the downside is that it takes longer to do the work.
Hot mix asphalt is never made in the wintertime in Minnesota. Nobody does paving in the winter; it’s too expensive to fire up the burners and keep a plant hot, and road construction is not practical in the cold winter months. For 60 years, Public Works had its own concrete batch-making plant in Minneapolis and our own asphalt production plant. About a dozen years ago, it got to the point where it was less expensive to buy asphalt than to make it. We decommissioned our plant, tore it down and it’s gone. Now the city buys hot mix from commercial asphalt plants. St. Paul still has a very old plant of its own, which is great because we can get hot mix a little earlier in the spring and a little later in the fall than we can from the commercial plants.
A good defense against potholes is a good offense. A year or two after you pave a road, you already start to see cracks in the pavement. Sealing those cracks, or sealing the joints in concrete pavements, keeps the water out and helps prevent potholes. Seal coating or resurfacing are good pothole prevention strategies to deter surface deterioration and keep water out. Pavements that are new, or have been seal coated or resurfaced, will have fewer problems than older pavements.
People can get frustrated when it takes a long time to fix potholes. But we can’t be everywhere at once. We have limited budgets, limited numbers of people, limited resources to tackle the problem. We chase them and repair them as best we can. Over the last decade, the city has invested in good pothole prevention strategies, so while there still are potholes every year, there are actually a lot fewer than there could be.
— As told to Zac Farber