Tag Archives: patching

Patching pavement with microwaves and magnetite

On Wednesday, I had a chance to watch a demonstration of a uniquely Minnesotan pavement patching technology that combines an industrial-strength microwave with a special asphalt mix. What makes it “uniquely Minnesotan?” In addition to having been developed by University of Minnesota researchers and a Monticello-based company (and with some funding from MnDOT), this innovative method involves a special asphalt mix using magnetite, a mineral that abounds on Minnesota’s Iron Range.

It also addresses a very Minnesotan transportation problem: winter pavement repair. In the video above, Kirk Kjellberg of Microwave Utilities, Inc., highlights some of the benefits of using the 50,000-watt microwave to heat the pavement during patching. In addition to creating a longer-lasting patch, the microwave is considerably faster than many alternative techniques. The technology is still relatively new, but its supporters claim it allows for pavement repairs in the middle of winter that are as strong and durable as the ones road crews do in the summer.

The demonstration, which was organized for members of the Local Road Research Board, took place at MnDOT’s District 3 training facility in St. Cloud.

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The people (and machines) who fix Minnesota’s potholes

In Minnesota, with our often wildly unpredictable weather and constant freeze-thaw cycles, potholes are a fact of life. Anyone who’s climbed into a motor vehicle in the last month or so has doubtlessly encountered countless reminders of this dismal reality. Fortunately, we have a small army of public works professionals devoted to eradicating this perennial nuisance. The Minnesota Local Road Research Board recently produced this video, which nicely explains the various methods used to combat potholes in Minnesota.

Potholes form when water invades cracks in the pavement and infiltrates the soil beneath it. When that water freezes, it stretches the road surface, causing the fractures to expand. After a few cycles of freezing and thawing, the pavement begins to buckle and eventually collapses under the weight of passing traffic, creating disruptions in the road’s surface.

Road crews use a variety of methods to fill potholes. The simplest method is the “throw-and-go” procedure, in which workers simply shovel an asphalt mixture into the pothole and pack it down until the road’s surface is smooth. A related method is “throw-and-roll,” where the patch is compacted using an asphalt roller.

Other methods include:

  • “semi-permanent” patching, in which workers clear the pothole of moisture and debris and then square the edges with a pavement saw before applying the patch;
  • “spray injection,” which involves using specialized equipment to blast water and debris out of the pothole before spray-filling it with asphalt mix and finally applying a dust coat of dry aggregate on top; and
  • “slurry” or “microsurfacing” crack filling, in which a slurry of aggregate, asphalt emulsion and mineral filler is placed over a crack in the pavement and leveled off using a squeegee.

This Asphalt Pavement Maintenance Field Guide (PDF), co-funded by MnDOT and produced by CTS, provides a handy how-to guide to pothole patching and other types of pavement repairs commonly applied by public works professionals in Minnesota.

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