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NRRI to test taconite tailings for construction durability
You’re in your car on the way to work. Suddenly you slow down, realizing that a construction truck, which is patching a hole in the roadway, is dead ahead. As you slowly pass the construction scene, it occurs to you that something is not quite business as usual. That truck is patching a hole in January.
No it’s not a strange dream – it’s a not-too-distant possibility if technology that’s being tested this construction season by the University of Minnesota Duluth Natural Resources Research Institute and the Minnesota Department of Transportation proves successful.
For a number of years, NRRI researchers have been developing new and value added uses for the region’s abundant natural resources – namely timber and taconite. One such new use, which has been under exploration for the past several years, is the mixing of taconite tailings with asphalt for use in roadway patches and construction.
Using mining waste rock in road aggregate is not a new application. Although widespread use has yet to be established, taconite waste rock has been used in road construction for more than 50 years. One notable example is the Brainerd Speedway, which was repaved with waste rock aggregate in 2002.
Coupling microwaves with the use of waste rock could make the application more attractive in coming years. Why? Because combining taconite aggregate with microwaves could allow road repairs to take place in the dead of winter, when traditional hot mix is not available, and cold weather makes taconite mix cool off too quickly.
There are other factors that make taconite aggregate an appealing alternative. In addition to the inaccessibility of hot mix during the winter months, taconite mix may fill another niche – use in remote areas that are too far from a hot mix plant to make transporting financially feasible.
“(Traditional) hot mix gives you good quality repairs,” said MnDOT District 1 Engineer Duane Hill, “but it’s not always available in this region in remote areas.”
And, in 2007, NRRI researchers concluded that aggregate shortages also could become commonplace in metropolitan areas during times when infrastructure is being expanded or rebuilt. That potentially makes the use of taconite aggregate possible outside this region, where transportation of taconite waste is less of an issue.
After a number of years of testing and formulation research, NRRI has developed taconite waste rock mix that’s been tested in the Duluth area as well as on the Iron Range. The formulation shows promise.
“This product can be mixed very quickly and sets up very quickly,” said Larry Zanko, NRRI senior research fellow. “It can be driven on in as little as a half an hour.”
The use of microwaves adds the benefit of being able to patch holes in winter. With a truck-mounted microwave producer, construction crews can heat concrete or other materials around the patch as well as the patch material itself – allowing better adhesion between old and new road surface.
Pairing microwave technology with taconite aggregate use has been under exploration for the past eight to nine years, according to Zanko. He said the concept was brought to NRRI researchers’ attention by another researcher, David Hopstock. Taconite waste rock, which contains about 26 percent magnetite, can absorb microwaves very readily – making it an ideal candidate for such cold weather repairs.
“In theory, we should be able to do a patch when it’s 10 below as well as when it’s 80 above,” said Hill.
While the use of microwaves to thaw the ground for road repairs had been identified, it was less clear how to implement microwaves effectively.
To clear that hurdle, NRRI researchers took a cue from a Monticello company, Microwave Utilities Inc., which was using similar technology to heat the ground for wintertime utility line repairs. Ground thawing with microwaves, according to information from the company, reduces time on winter projects by 90 percent.
Microwave Technologies President Vern Hegg said his company developed the use of microwaves as “a better way to thaw the ground out.” Burning propane was previously a widely used method for ground thawing, but it takes 24 to 36 hours to complete. Microwaves have the ground thawed for utility installation in about one hour, he said.
“Our system is very similar to your microwave oven at home,” Hegg said. Microwave Utilities units, he added, seal to the ground, making a barrier that prevents emissions.
Over the course of this construction season NRRI, working in coordination with MnDOT, will be testing the durability of taconite waste rock aggregate.
Zanko doesn’t think the use of taconite in road construction is likely to replace its primary use – making steel – anytime soon. Nonetheless, discovering and implementing other uses for taconite or its waste rock strengthens the iron mining industry locally and provides possible new revenue streams and jobs. The research also benefits private companies, like Microwave Technologies, which is working closely with researchers to improve their own microwave units.
“These are niche applications,” said Zanko. “But, they have the potential to generate value.”
For officials at MnDOT, who also have been experimenting with the use of infrared heat in pothole repair, taconite aggregate and microwaves offer options. “It’s another tool in the toolbox,” said Hill.
Zanko said NRRI officials are working with mining companies on the Iron Range to develop long-term supply. He declined to provide further details on those talks.Previous Construction Articles:
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