A Brief History of the Use of Taconite Aggregate (Mesabi Hard RockTM) in Minnesota (1950s – 2007)

Abstract

Taconite aggregates (collectively termed Mesabi Hard Rock™) have been used as construction aggregate in Minnesota for nearly 50 years, dating back to the early days of the taconite industry. Coarse taconite tailings are a ready-made, free-draining, fine aggregate equivalent suitable for use as select granular and fine filter aggregates. Their angular interlocking form, when placed with water and covered with Class 5, produces sound embankment fill material. Their hardness, strength and durability produce superior wear and friction properties in bituminous mixes. This, coupled with 100% fractured faces, makes them ideal for Superpave mixes. Their cleanness (very low -200 mesh) makes them a valuable tool for adjusting volumetric properties in bituminous mix design. Crushed taconite rock brings the same hardness, strength and durability to the coarser aggregate size fractions, making it ideal for crushing to desired specifications for use as fill, filter material and the coarse aggregate component in bituminous and concrete mixes. Historically, taconite aggregate products have been used most when road construction, maintenance, and repair projects are in close proximity to the taconite operations, i.e., on the Mesabi Range. The 1970s and 1980s saw the use of coarse taconite tailings spread to the Twin Cities metropolitan area, as well as to the southern and western reaches of the state for use in bituminous overlays and surfacing. The 1990s and 2000s saw taconite aggregates become a staple of Duluth area bituminous contractors and road constructors, to the degree that they are used in some capacity in nearly every project. Millions of tons of taconite byproducts are produced every year in the mining and pellet production process. Couple this with nearly 50 years of production and the enormous size of this resource becomes obvious. While much of this material is consumed by the taconite mines for day to day operations (haul roads, tailings dams, shovel pads, drill hole stemming, etc.), much remains stockpiled and available for use. Infrastructure already in place for shipment of pellets (roads, railroads, and Lake Superior docks and ship-loading facilities) can be accessed for shipment of aggregates throughout the United States and beyond. This report is a historical narrative of the highlights of taconite aggregate usage as road construction aggregates in Minnesota. It documents how taconite byproducts have evolved from stockpiled "wastes" to become premium "in-demand" aggregates suitable for meeting today's infrastructure needs.