A northern Minnesota mining byproduct could provide a more affordable option for a highly effective, but expensive pavement safety treatment called High Friction Surface Treatment (HFST), and help expand its usage across the state.
Real field data is currently lacking for a direct comparative performance evaluation of Mesabi (taconite) friction aggregate versus the standard calcined bauxite used in HFST applications.
Calcined bauxite has been given a preferred status relative to HFST usage by the Federal Highway Administration (FHWA), but is imported, expensive, and energy-intensive to produce.
A recycled/byproduct alternative like Mesabi friction aggregate may still provide adequate or comparable field skid resistance performance and is significantly less energy-intensive to produce. This treatment could be applied using construction equipment already widely used across Minnesota.
This treatment is particularly of interest to Minnesota counties. County highways often have sharper horizontal curves than state highways and these curves can be dangerous to motorists. When flattening the curve is not possible (due to cost and right-of-way constraints), increasing the friction of the road improves safety.
“Safety is a top priority for county engineers across the state—our job is to provide safe roads for the public,” said Tracey Von Bargen, Grant County Engineer and technical liaison for the project.
“Mesabi friction aggregate may be a more financially attainable treatment for Minnesota counties than calcined bauxite. Adding friction to our roads—especially along curves—is one way to get us closer Toward Zero Deaths.”
In a new study, researchers will install HFST systems using both aggregate types.
This summer, a standard HFST application was applied on several roadway curves in St. Louis County (the first on a Minnesota county road system – see video); it will be compared with test sections of taconite-based HFST to be applied later in the northern Minnesota county.
The project team will evaluate whether Mesabi friction aggregate can partially or fully replace calcined bauxite in HFST applications by considering appropriate treatment installation alternatives, including but not limited to:
- Various adhesion methods, such as epoxy, asphalt binder, and micro surfacing
- Varying blends of Mesabi friction aggregate and calcined bauxite including 100% Mesabi friction aggregate and 100% calcined bauxite (for comparison)
- Appropriate aggregate gradation
Evaluation criteria may include:
- The cost to install and maintain, along with a comparison to standard HFST installations using calcined bauxite
- Skid resistance test comparisons, monitoring performance, and evaluating wear over time in the field and the lab, including the effect of snow and ice maintenance operations (i.e., snow plowing)
- Assess effect of aggregate color on pavement surface temperature and impact on duration of snow and ice coverage
- Assess impact of surface treatment on the retention and effectiveness of de-icing chemicals
- Estimated Start Date: 07/29/2020
- Estimated Completion Date: 12/31/2023
- Funding: Local Road Research Board
- Principal Investigators: Lawrence Zanko, Mihai Marasteanu, Manik Barman
- Technical Liaison: Tracey Von Bargen
Details of the research study work plan and timeline are subject to change.
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