IN MINNESOTA, IRON-ORE TAILINGS REPLACE VIRGIN AGGREGATE

In Minnesota, taconite tailings have been used successfully for decades as a replacement for virgin aggregates in road construction, and could be exported elsewhere in the country, report Julie A. Oreskovich, Marsha Meinders Patelke and Lawrence M. Zanko, Natural Resources Research Institute, University of Minnesota-Duluth, in their paper, “Documenting the Historical Use of Taconite Byproducts as Construction Aggregates in Minnesota: A GIS-based Compilation of Applications, Locations, Test Data, and Related Construction Information.”

Taconite is a low-grade iron ore, pelletized for blast furnace reduction. Even as virgin aggregate resources are getting more difficult to permit and extract, Minnesota's taconite mining industry generates more than 125 million tons of mining and processing byproducts annually that hold aggregate potential of trap-rock quality, the authors write.

“Materials such as blast rock, coarse crushed rock and coarse tailings (collectively known as Mesabi hard rock) have been staples of northeastern Minnesota road construction for over four decades,” they say. “Infrastructure is already in place to move these materials to markets throughout the country to augment local aggregate resources.”

Because these highway construction applications are not widely known outside of northeastern Minnesota, the authors assembled related test data and documented how and where taconite byproducts have been used. Letters, interviews, site visits and searches of archived records were the primary modes of data collection. The result is a project report with a stand-alone Microsoft Access (or Excel) database and an ArcView GIS product containing mappable Mesabi hard rock usage locations with accompanying data.

The resulting databases can be queried on a variety of topics or attributes. The researchers found more than 400 documented usages in Minnesota from 1960 to 2006, including 1,120 usage miles of roadway pavement and fill. The primary applications are for bituminous pavement (with desired hardness, durability, with 100% fractured faces ideal for Superpave mixes); and fill (with desired free-draining attribute and containing a ready-made fine aggregate equivalent). The Minnesota Department of Transportation is the top user.