A growing demand for paving aggregates and an overabundance of plastic waste may create a sustainability partnership. Plastic is a significant contributor to the waste stream in the U.S. Less than 10% is recycled and repurposed. Transforming plastic waste into useful materials like road pavement could have numerous environmental, economic and sustainability benefits.

Local agencies and MnDOT explored the feasibility and material performance of plastic waste incorporated into both asphalt and concrete pavement mixes. Information gathered from recycled plastic material providers informed the choices of materials to test in the laboratory. Researchers analyzed mixing processes, material behavior and durability of both asphalt and concrete pavement mixes. While further research and field testing is needed, the plastic-modified pavement mixes showed high potential for equal or improved performance and significant sustainability benefits.

The use of recycled materials in place of virgin materials to manufacture corrugated HDPE pipes has environmental and fiscal benefits. Investigators field-tested corrugated pipes manufactured with recycled materials and pipes manufactured with all virgin materials to compare performance. No discernible differences were found between the two, with satisfactory function and performance for both. A modified life cycle assessment and life cycle cost analysis identified areas of positive environmental impacts and opportunities for cost savings, respectively, by deploying corrugated HDPE pipes manufactured with recycled material.

Materials used to make pavement markings visible at night may also cause the markings to be slicker than surrounding pavement, especially in wet conditions. Bicyclists, motorcyclists and pedestrians have reported safety concerns when traveling over pavement markings. MnDOT and local agencies set out to explore how much friction pavement materials provide compared to the surrounding pavement.

Researchers tested a variety of pavement marking materials, and results showed that the friction of pavement markings did decrease over time and wear. Some additives, including locally available taconite, increased friction of certain marking materials. The project also assessed friction measurement tools to guide the agencies in producing the most cost-effective and consistent friction data. The agencies will continue to assess the best pavement marking materials to maximize safety for all road users.

Implementing strategies to reduce early-age cracking in bridge decks may lower costs over the service life of a bridge. For bridge deck installations, investigators adjusted the concrete mixture, regulated temperature differences between concrete and support girders, and reduced spacing between reinforcement bars to minimize this cracking. Results indicated that these strategies can mitigate early-age cracking and save taxpayer dollars.

Locally produced taconite is a potential replacement for imported calcined bauxite as an aggregate used to add friction to roads. Investigators evaluated both taconite and calcined bauxite in high friction surface treatments on local roads near Duluth, Minnesota. Test results showed that taconite and calcined bauxite produced friction numbers that were 40% to 50% higher than the chipseal control test section. Taconite’s performance was comparable to calcined bauxite’s, averaging only 6% lower friction results while reducing environmental impacts and costs.

The supply of high-quality aggregate used to construct roads in Minnesota is dwindling. However, lower-quality aggregate is plentiful and represents an opportunity to reduce road-building expenditures. This project evaluated the performance and cost-effectiveness of varying aggregate quality and other associated materials to develop optimized pavement designs. Results indicated that flexible pavements serving moderate traffic levels can perform effectively using low- to medium-quality aggregate materials with properly optimized thicknesses, which offers a substantial reduction in construction costs and avoids a reliance on premium aggregate sources.

The use of centerline rumble strips (CLRS) has been shown to reduce severe head-on crashes on two lane roads by up to 64%. The FHWA has included rumble strips in their new “Proven Safety Countermeasures” initiative, which may result in more widespread use of rumble strips. Installing CLRS in asphalt pavements may accelerate deterioration of the pavement at the longitudinal construction joint. Recent research has measured this effect and suggested chip sealing new rumble strips as a preventive measure; however, chip sealing following installation may not be practical or desirable for many reasons. Other materials that have a demonstrable impact on centerline joint durability, without sacrificing the functionality of the rumble strip, have been described, namely Void Reducing Asphalt Membrane and Rapid Penetrating Emulsion. This project evaluated the efficacy of these material methods for improving CLRS durability while maintaining safety through the use of full-scale field projects.

This project developed guidance and recommendations for integrating environmental impacts into the procurement process for transportation projects. Beginning in 2028, an environmental product declaration (EPD) will be required for projects using concrete or asphalt. An EPD summarizes a product’s potential to impact the environment and provides a standard reporting system that is consistent with rules set by product stakeholders. The project developed a benchmarking methodology to establish environmental impact reference values, created a data collection protocol and life cycle information model to estimate production and construction environmental impacts, and mapped impacts to specific pay items.