Pothole Rangers using the current procedure for patching.
Filling pothole using injection/spray patching method.
Filled pothole using the injection /spray patching method.
Always in search of making the most efficient use of our manpower and limited resources , this past week, SDOT began a two-year test on a new product and method of filling those pesky potholes in Seattle’s streets. The product is called an “injection patch” and requires a special truck developed just for applying fill with a tar and rock mixture. The truck heats, mixes and blends the patching material and then sprays it into pot hole. Only one person is needed to drive and carry out the work. The force with which this blend is sprayed totally fills a pot hole.
No northwest city currently uses this spray patching technology. Seattle’s current procedure is also used by other northwest cities including Portland, Vancouver, and Olympia. That procedure requires a three-person team that must first jackhammer the hole, dig out the sides of the hole so it is no longer round, but rather a square shape, and then fill the space with an asphalt mix which is the same as that used to pave streets. The square shape is necessary because the asphalt mix can’t be sprayed into place and thus does not fill in every crack and cranny of an uneven shaped hole. A second method is also used to make fast repairs with an asphalt mixture and is aptly named “throw and go.” With this procedure, the Pothole Rangers simply heat the asphalt, smear it into the hole, and then move on to the next work location.
This past week SDOT began testing the strength and durability of the three types of repairs and patching materials in potholes on three blocks of N 85th between Wallingford Avenue N and Aurora Avenue N. One block of potholes was injection or spray patched, on a second block the potholes were jack hammered out and filled with the standard asphalt mix; and the third block of potholes received the “throw and go” treatment. Over the course of next two years, these three blocks will be monitored every three months and the data will be compared to determine which procedure and fill proved to last longest.
Why test the three types when this “new” patching method only requires one worker, is quick and is successfully used in many states? For one thing, the truck may do it all, but it comes with a hefty price tag – several hundred thousand dollars. The company which manufactures the trucks loaned one to the city for a day of testing. While other cities have found spray patching successful, they have a different kind of base beneath their roads. Seattle is largely built on clay-like material that is not hard and when heavy vehicles such as buses and trucks travel on the streets the clay beneath is “squishy” and results in the development of pot holes in the city’s surface streets. In contrast, other cities such as Denver, which has far more extreme weather, has a very hard base under laying its streets. Streets with a hard base tend to hold up to the weight of heavy vehicles and develop potholes in the traditional way – as a result of freeze- thaws. In this situation, water seeps into cracks and then expands when it freezes; when the frozen water thaws the crack has become a pothole.
Stay tuned in as we track the results of this potentially faster, cheaper, better way of filling potholes.