Waste products as road materials

This research summary is part of the final deliverable for Report 2024-23, "Re-Use Of Minnesota Waste Material In Sustainably Designed Soils: Part 2, published in September 2024

Minerals, forestry, agriculture, and industrial activities in Minnesota generate substantial by-products and waste. Strategies to reuse or recycle these can reduce landfill waste, enhance public health, conserve resources, and cut costs and emissions. Building on the frameworks by Johnson et al. (2017), Saftner et al. (2019), and Saftner et al. (2022), this project extended its scope across Minnesota to include materials like dredge sediment from Mississippi River, RCA (recycled concrete aggregate) and VersaLime. Researchers identified, selected, and characterized various waste, by-products, and commercial materials statewide, as well as tested engineered soil mixes for roadway applications, assessing their stormwater retention and support for native plants. Laboratory methods characterized these mixes, which were implemented and evaluated in situ. A preliminary environmental life cycle assessment (LCA) was also conducted quantifying the environmental impacts of the engineered soil mixtures. Results were compiled into a design guide for the Minnesota Department of Transportation (MnDOT) engineers.

This report is meant as a state of the art on utilization of solid waste material for road construction and maintenance. There are many waste materials, but in Minnesota three products are of prime interest because they are available in such large quantities. These are: Taconite Tailings, Fly Ash, and Boiler Slag Much study has been done on some of these large volume materials. Some of the successful uses found for these products are embankment fill, subbase, base, stabilize for soil or aggregate, paving aggregate, and bituminous mix components. This report undoubtedly is not the "last word" on the subject of solid waste utilization. Some materials or uses may have been overlooked or neglected, but it is hoped that the overall local state picture is well represented. This report has attempted to show that there are some large volume waste materials, there are bona fide uses for them, and utilization could be expanded with some effort. This also applies to lesser volume materials that sometimes aren't recognized as being usable.

This is a project summary of the research that went into Report 2013-15, " Recycled Asphalt Pavement: Study of High-RAP Asphalt Mixtures on Minnesota County Roads."

This research investigated the effects of incorporating recycled concrete aggregate (RCA) at low replacement levels on the properties of concrete. Four different RCA sources were used, each with different aggregate properties. For each source, replacement levels of 5, 10, and 15% were tested and compared to a control group, which had no RCA. Of the four RCA sources investigated, three had similar levels of absorption capacity and percent fines, while one source had higher levels of both properties. RCA replaced virgin aggregate of a similar gradation and replacement was on the basis of volume. Fresh and hardened concrete properties were tested, including air content, super air meter (SAM) number, slump, workability via the box test, compressive strength, flexural strength, elastic modulus, Poisson’s ratio, coefficient of thermal expansion, surface resistivity, freeze-thaw durability, and unrestrained shrinkage. Digital image correlation was used to visualize strain fields during compression testing. A statistical analysis was conducted to determine if any observed differences in hardened properties between the test mixes and the control group were statistically significant. This research found that using up to 15% of an RCA with reasonable values of absorption capacity and percent fines would not negatively impact most concrete properties. It also provided an outline for future research to develop a specification to define what constitutes reasonable values of RCA properties for future use.

This is an Innovation Update that shows the how MnROAD uses fly ash in pavement design, after the release of three research reports (2009-27, 2007-12, and the 2007 Low Volume Road & Farm Loop (Cells 33, 34, 35, 77, 78, 79, 83, 84) Construction Report.)

This is a project summary of Report 2010-09, "Incorporation of Recycled Asphalt Shingles in Hot-Mixed Asphalt Pavement Mixtures."

The goal is to assess potentially suitable, available aggregate resources that could supply an abundant, high quality, low cost aggregate for roadway use. This effort will help pave the way to use this material in the near future, especially in areas that aggregates are becoming scarce. Currently this aggregate material from the Iron Range is considered "waste product" relating to their taconite production, but it has high potential for its use in our roadways which includes the use of fine to coarse taconite aggregate materials in hot mix asphalt, concrete mixes, and other pavement applications for both its constructability and field performance over time. This would help create a greater comfort level for the use of this aggregate and help promote its use in the state and the nation

This Technical Summary pertains to the LRRB-produced Report 2009-32, “Hydraulic and Mechanical Properties of Recycled Materials,” published October 2009.

This Technical Summary pertains to the LRRB-produced Report 2009-27, “Use of Fly Ash for Reconstruction of Bituminous Roads,” published August 2009.