In the far northern reaches of the continental U.S., pavement maintenance supplies can often be in short supply, depending on the time of year. This can seriously impede pothole patching as asphalt plants close for the winter. The City of Fargo, ND, only 160 miles from Canada, took matters into its own hands to extend its road patching season and provide a better solution to potholes for its citizens. The result of their efforts was better roads for surrounding communities as well. “The throw-and-go method of cold mix patching was not even lasting a day when wet conditions were present,” explained Ben Dow, Director of Public Works for the City of Fargo.
With winter lasting up to five months in the upper Midwest, the freeze/thaw effect on Fargo roads can be a double whammy. Moisture from snow melt can often penetrate pavement surfaces, causing subgrade saturation. Once moisture has accumulated in the subgrade and the temperatures drop, the water in the subgrade freezes and expands, pushing both underlying base material and the pavement surfaces upward. The void in the underlying soil allows for the collection of additional moisture in the subgrade and pavement settlement. “The end result is potholes, alligator cracking, pavement edge breaks and shifting concrete causing uneven roadways,” said Dow. “We really needed a tool to make our repairs last longer.”
Four years ago the city tried a spray-injection patcher manufactured by Cimline Pavement Maintenance Group in Plymouth, Minn., and found it both provided a more permanent fix and reduced costs. “The DuraPatcher enables our crews to build up broken pavement edges and potholes from March through November,” Dow noted. “We have found it to be a tried and true method, especially on our arterial roads.” The bonus of spray-injection patching is the versatility of repairs that are possible, something that hot mix and cold patch cannot do. “In addition to the obvious pothole filling, spray injection can execute repairs such as pavement profiling, water control and immediate repairs to raised manholes and shoulder failures,” explained Dow. The city also realized better utilization of its personnel, an important consideration with more than 2,000 lane-miles to maintain.
The spray-injection method provides a permanent repair by spraying a mixture of emulsion-coated aggregate with sufficient force to compact the mixture as it is applied in layers. The operator patches a pothole in four steps delivered through one nozzle:
1. Clean the pothole with forced air.
2. Apply an emulsion tack coat.
3. Spray the hole with emulsion-coated aggregate.
4. Cover the finished patch with dry aggregate so traffic can resume immediately.
The DuraPacher is available in truck- or trailer-mounted configurations. The City of Fargo purchased a trailer-mounted unit that is towed by a dump truck to supply the aggregate.
While Dow had a permanent pothole patching solution, he was faced with limited availability of CRS2 emulsion—the carbon disulfide asphaltic binder that is used by the DuraPatcher system. Dow said, “Sometimes CRS2 would not become available from the local distributer until June or July, which delayed pothole repair well after the fact of pavement disintegration in early spring.” The solution was to invest in an onsite 6,000-gal emulsion storage tank. City workers recognized that the emulsion tank was the key to their pavement preservation program’s success.
In a year’s time the city took delivery of approximately 100,000 gal of CRS2 emulsion. The Public Works Department used roughly 25,000 gal for its own purposes. In a unique arrangement, the city offered to supply other government agencies from its supply of emulsion for roughly 10% over its purchase price. As a result, five surrounding communities were able to make spray-injection repairs, using their own or rented DuraPatcher equipment. The result was that improved pavement preservation spread to surrounding areas.
When asked to calculate the economic savings of using spray injection patching, Dow pointed out that there is no real comparison to previous repair methods. He emphasized that his team was unable to make successful pavement repairs from February to May each year because hot mix was not available and cold patch methods weren’t lasting. That’s why the comparison was so easy. “The profits on the sale of CRS2 to surrounding communities have been averaging a little over $19,000 per year, so we are currently looking at a five-year return on our investment in the tank at this point,” Dow noted.