Performance of Taconite Aggregates in Thin Lift HMA: Final Report - January 31, 2012

Abstract

This project was undertaken to advance the knowledge of the beneficial uses of taconite mining coarse tailings (taconite fine aggregate) for thin lift hot mix asphalt (HMA), to facilitate technical information gathering and marketing of such uses and properties, and to encourage the beneficial use of recycled/byproduct materials like durable and wear- and skid-resistant taconite (Mesabi) aggregates, recycled asphalt pavement (RAP), and asphalt shingles. In combination, the use of each is highly desirable because it promotes resource conservation, safety, and energy-saving. Outcomes of this study suggest that Mesabi rock and tailings products show promise as components of 4.75-mm Dense-graded, Stone Matrix Asphalt, and Ultra-Thin Bonded Wearing asphalt mixtures. Laboratory and field investigations of taconite tailings should continue. The Mesabi rock can be incorporated in standard Superpave, SMA, and fine/sand asphalt mixtures in upcoming construction projects. In each case construction and long term field performance should be evaluated. The investigators conclude that taconite-based thin lift HMA mixes that also incorporate RAP should be recognized as an environmentally sound, i.e., combining the use of byproduct and recycled/reclaimed materials, and high-quality option for HMA pavement rehabilitation and preservation. Collectively, the material testing results suggest that thinner wear-course pavements made from appropriately designed taconite-based mixes can match or exceed the service life of conventional MnDOT Level 4 mixtures. If extended service life is realized, then taconite fine aggregate could be a cost-effective choice at end-user locations where high-quality local aggregate sources are lacking or absent. These enhanced performance attributes can add intrinsic value to taconite materials and make them more desirable to use and more cost-effective to transport longer distances, thereby improving and broadening their near- and long-term potential for regional and national highway infrastructure projects.