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This report evaluates the technical and economic viability of using coarse taconite tailings for construction aggregate purposes by analyzing the results of tests run on their physical, geological, mineralogical, and chemical properties as well as doing a market analysis.

In support of a broader MnDOT effort to evaluate current practices, materials, and policies for pavement patching and repair for both asphalt and concrete pavements, the University of Minnesota Duluth Natural Resources Research Institute (NRRI) conducted additional evaluation, refinement, field testing, and performance monitoring of two taconite-related approaches to pavement repair that rely on mixes/techniques that contain (or are enhanced by) taconite mining byproducts and co-products. The first taconite-related approach to pavement repair uses a rigid pavement/pothole repair compound formulation developed and patented by NRRI that is fast-setting, taconite-based, and contains no petroleum or Portland cement. Depending on the formulation, the repair compound can be water-activated or activated by a chemical solution. A water-activated formulation referred to as Rapid Patch was the focus of the investigation. The second taconiterelated approach to pavement repair employs a high-power (50kW), vehicle-based (truck-mounted) microwave system for in-place pothole/pavement repair/recycling in which magnetite and/or magnetite-containing aggregate (taconite rock) can enhance microwave absorption and therefore the systems performance. The two repair alternatives evaluated during this project merit further development and consideration, as the field performance of both suggests they have long-term potential for more widespread use. Based on feedback from maintenance personnel who used and/or observed both repair alternatives during the project, both alternatives would benefit from operational modifications that would reduce the deployment time required to complete a repair and increase the number of repairs that can be accomplished during a single shift. Doing so would likely lead to greater acceptance and more widespread use.

This project refined the Natural Resources Research Institute's (NRRI's) patented taconite-based repair compound, explored equipment options, and field tested/demonstrated a low-cost mechanized system that can efficiently mix and place the repair compound in larger quantities while minimizing or eliminating direct contact and hand mixing by maintenance personnel. The rigid, taconite mineral-based, all season rapid-setting repair compound contains neither petroleum nor portland cement. As such, its environmental footprint is much smaller than cold-mix or hot-mix asphalt products, mastic, and portland cement-based repair compounds. The refined and optimized formulation utilizes relatively low-cost and abundant mineral byproducts and co-products; and the mechanized deployment system makes use of relatively inexpensive commercially available, i.e., off-the-shelf; equipment; compared to single-bucket mixing. Larger-scale continuous mixing remains a challenge and is still under investigation. The expected economic benefits include cost savings for both raw materials and maintenance labor. In addition, the rapid-setting nature of the formulation combined with a mechanized deployment system would allow pavement and pothole repairs to be conducted faster and with moving traffic control, thereby avoiding lengthy traffic-disrupting lane closures. Key project outcomes are lower costs, better-quality and longer-lasting repairs, and improved productivity.

Expansion and maintenance of roadway infrastructure creates a demand for high quality paving aggregates. Taconite industry rock and tailings are a potential source of virgin paving aggregates. Currently there is limited information available for implementing these products in construction design specifications. Preliminary information of product performance within current design constraints is valuable to both state design engineers and to future pooled-fund studies. This information can identify the potential for using these products in surface courses or possibly for use in rich-bottom leveling layers. This study examined the viability of utilizing these products in the Minnesota Department of Transportation (Mn/DOT) Superpave bituminous mixture design specifications. As part of the study 40 laboratory specimens were produced from 11 asphalt mixtures and then evaluated for asphalt content, air voids, and aggregate gradation. This report summarizes the results of the laboratory mixture evaluation.