To limit the environmental impacts of transportation projects, agencies need to identify the sources of greenhouse gas emissions throughout a project’s life cycle. By identifying specific sources and activities that generate emissions, the Minnesota Department of Transportation (MnDOT) can take steps to reduce its carbon footprint. This project explored the use of life cycle assessments and Environmental Product Declarations to measure and reduce the emissions associated with MnDOT paving projects, specifically the transportation of asphalt from production plants to job sites and subsequent paving activities.
Continue reading Incorporating Environmental Assessments of Paving RoadwaysCategory Archives: Materials and Construction
New Project: Holistic design and selection criteria for unbound geomaterials used in pavement systems
Unbound geomaterials used in roadway base layers strongly influence pavement durability, yet current practices in Minnesota often focus narrowly on gradation and index properties. This research seeks to fill that gap by examining mechanical behavior alongside hydraulic, water retention, and suction characteristics to better understand how these materials perform within real-world environmental and pavement systems.
Pavement base layers serve two essential purposes: providing mechanical support that prevents fatigue, settlement, and rutting, and enabling drainage that protects the structure from elevated pore pressures and freeze‑thaw damage. Although millions of tons of these materials are used annually, past studies rarely consider the full interaction between the base layer, surface conditions, and environmental factors.
The project’s primary goal is to develop a new holistic guideline for selecting unbound geomaterials and designing pavement foundations. By integrating both mechanistic and hydraulic considerations, the long‑term objective is to support a shift toward design approaches that enhance roadway performance while reducing maintenance needs and costs.
The Objectives:
This project aims to develop a new holistic unbound geomaterial selection and pavement foundation design guideline. This will be achieved through the completion of four primary objectives:
- Review of current roadway foundation design practices and guidelines of MnDOT and local counties and cities in Minnesota.
- Collection and analysis of existing data from the literature on the topic (including the extensive previous work of the research team).
- Developing a holistic design and material selection framework that explicitly takes material drainage characteristics, material mechanical characteristics, unsaturated soil mechanics properties, and prevailing environmental characteristics into account.
- Extensive laboratory and field testing to demonstrate and verify the new approach.
- Evaluating and modifying the pore suction resistance factors and seasonal multipliers used in MnPAVE.
Project Details:
- Estimated Start Date: 7/10/2025
- Estimated Completion Date: 6/30/2027
- Funding: MnDOT and Local Road Research Board
- Principal Investigator: Bora Cetin
- Co-Principal Investigators: Tuncer Edil, Michele Lanotte, and William J. Likos
- Technical Liaison: Ceren Aydin
Details of the research study work plan and timeline are subject to change.
To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.
Preventive Road Sawing and Sealing to Reduce Maintenance Costs
Asphalt pavements will inevitably begin cracking and require maintenance to preserve an adequate level of service. However, preemptively sawing and sealing roads at prescribed locations can reduce cracking and improve maintenance predictability. To help the state’s transportation agencies better manage pavement deterioration, the Local Road Research Board sought to compare the performance of a lower-cost unmodified asphalt binder using the saw-and-seal method with that of a higher-cost polymer-modified asphalt binder without using saw and seal.
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New Project: Design guidance and best practices for the use of light fill for sustainable road construction
Lightweight Fill (LWF) materials—including Tire Derived Aggregates (TDAs), expanded shale/clay, foamed glass, and recycled glass aggregates—show strong potential for sustainable road construction, yet important knowledge gaps remain. Their environmental impacts, long‑term performance, and construction requirements are not fully understood, especially under Minnesota’s freeze‑thaw cycles and high groundwater conditions. Concerns such as leachate production, potential trench settlement, and challenges faced by local road departments highlight the need for further investigation.
This research seeks to address these gaps by reviewing existing practices, evaluating both environmental and mechanical performance, and developing data‑driven recommendations for using LWF materials in road construction. A detailed assessment will help clarify how these materials behave in pavement structures and embankments and how they interact with water‑sensitive environments. A decision matrix will be used to compare LWF materials and support future project planning.
To achieve these goals, the study will evaluate environmental impacts such as leachate risks, analyze long‑term structural integrity, and conduct Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) to assess sustainability and financial feasibility. The research will also develop recommended construction techniques that improve performance and support Minnesota’s climate goals and broader sustainability initiatives.
“Lightweight fill materials show promise for sustainable road construction, and Minnesota looks to learn from what has been done previously,” said Andrew Witter, Sherburne County Public Works Director and County Engineer. “This project will evaluate how these materials behave in local conditions and develop guidance for local counties and cities. The results will help agencies make informed decisions for the benefit of the transportation infrastructure in Minnesota.”
The Objectives:
- Document existing research and practices related to LWF materials in road construction.
- Evaluate the environmental impacts of LWF materials, focusing on leachate risks and interactions with water-sensitive environments.
- Analyze the long-term performance and structural integrity of LWF materials in both pavement structures and embankments.
- Compare LWF materials in a decision matrix to guide future project decisions.
- Perform Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) to assess the sustainability and financial feasibility of LWF materials.
- Provide recommendations to develop construction techniques that optimize the use of LWF materials and align with Minnesota’s climate goals and broader sustainability initiatives.
Project Details:
- Estimated Start Date: 06/25/2025
- Estimated Completion Date: 06/30/2027
- Funding: Local Road Research Board
- Principal Investigator: Michele Lanotte
- Co-Principal Investigators: Angela Farina
- Technical Liaison: Andrew Witter
Details of the research study work plan and timeline are subject to change.
To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.
Evaluating the Use of Stabilizers on Gravel Roads
Gravel roads often experience significant deterioration that requires costly maintenance. To mitigate this deterioration, transportation agencies can apply chemical stabilizers to improve aggregate cohesion. This project examined the mechanical, environmental and economic performance of five gravel stabilizers and three application methods to determine the best options for reducing deterioration.
Continue reading Evaluating the Use of Stabilizers on Gravel Roads
New Project: Are Current Rigid Pavement Roundabout Designs Working in Minnesota?
As roundabouts become more commonplace in Minnesota, the role they play in the improvement of traffic flow and safety increases. Although rigid roundabouts were originally designed with the assumption that they would behave like rigid pavements on motorways, their performance can be affected by the unique traffic patterns and stresses they experience. The irregular shapes of their concrete slabs face distinct braking, stopping, accelerating, and drainage conditions, which increase the likelihood of cracking and other forms of pavement distress. Heavy trucks navigating sharp curves add additional strain. While concrete pavements are generally durable, pavement wear is greatly affected by elements characteristic of roundabout design.
This research seeks to evaluate and improve the performance of concrete roundabouts in Minnesota, with the aim of extending their service life and increasing their overall effectiveness. The project will start with a comprehensive field survey throughout the state, collecting information on different roundabout designs and documenting the types and levels of pavement distress present. The data will be analyzed to identify performance trends and gain a clear understanding of each design’s advantages and shortcomings. In addition to the field investigation, the study will conduct an in-depth structural review of factors such as joint spacing, dowel bar placement, slab geometry, and drainage features.
Using insights from both the field observations and structural analysis, researchers will propose design strategies to improve the durability of Minnesota’s roundabouts. These recommendations have the potential to strengthen roundabout design practices and contribute to a safer, more dependable transportation system.
“With the rapidly growing number of concrete roundabouts being constructed throughout Minnesota, it is important that we monitor their performance and adjust our design methodologies to ensure that the traveling public can utilize them safely, while maximizing the investments spent on their construction and maintenance,” said Thomas Burnham, research operations engineer with MnDOT’s Office of Materials and Road Research. “This research project is set up to accomplish these goals.”
The Objectives:
- To measure rigid pavement roundabout performance for various traffic loads and design features.
- Using pavement system performance data, identify any design changes that could minimize maintenance.
- Create state-of-the-art guidelines and recommendations for improving the design, function and lifespan of concrete roundabouts in Minnesota.
Project Details:
- Start Date: 05/23/2025
- Estimated Completion Date: 05/31/2027
- Funding: MnDOT and Local Road Research Board
- Principal Investigator: Qingli (Barbara) Dai
- Co-Principal Investigators: Quang Tran, Zhanping You
- Technical Liaison: Thomas Burnham
Details of the research study work plan and timeline are subject to change.
To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.
Evaluating Recycled Asphalt Pavement Mixtures
The use of recycled asphalt pavement (RAP) materials in asphalt pavement construction provides numerous benefits, including reduced material costs, fewer environmental impacts and decreased demand for virgin aggregates and asphalt binders. While previous research has examined the performance of RAP materials, less attention has been given to their compaction properties. This project examined RAP mixtures with varying RAP contents to better understand their implications for pavement construction and environmental sustainability.
What Was the Need?
Road projects commonly use RAP in asphalt mixtures to reduce material costs, conserve virgin materials and improve pavement construction sustainability. However, concerns remain that increased RAP content could reduce compactability and crack resistance, negatively impacting pavement performance.
A better understanding of RAP material characteristics and mixture behavior is therefore critical to developing mixture designs that can reliably provide pavement durability and field performance. This project investigated RAP mixture design, compaction behavior at varying RAP contents, the impact of graphite nanoplatelet (GNP) modification and the low-temperature performance of different RAP mixtures.
What Did We Do?
This study analyzed RAP samples from three projects that used the same pavement mixture. Because RAP materials are not uniform, investigators evaluated the samples using processed black-and-white curves, chunk index, gradation, moisture content and binder content. For example, the chunk index measure material homogeneity, with higher homogeneity being desirable for mixing with virgin materials.
The first phase of testing analyzed RAP mixtures containing 25%, 40% and 50% RAP using a gyratory compactor. A mix design spreadsheet documented the proportions of virgin aggregates and RAP needed to achieve target gradations.
Next, investigators evaluated the compaction performance of GNP-modified RAP mixtures by comparing a 50% RAP mixture with and without 6% GNP at compacting temperatures of 135°C, 115°C and 95°C. Previous research indicated that adding GNPs to RAP mixtures can significantly improve low-temperature flexural strength and allow contractors to compact asphalt mixtures to higher densities, potentially improving pavement durability and performance.
Lastly, the project examined the low-temperature strength, fracture and creep performance of RAP mixtures by performing semi-circular bend fracture and bending beam rheometer mixture tests on blends containing 0%, 25%, 40% and 50% RAP.
What Did We Learn?
Gyratory compaction testing showed that mixtures with higher RAP contents required fewer gyrations to reach the target air void level. Specifically, the 50% RAP mixture achieved the targeted 5% air voids with fewer gyrations than the 40% and 25% mixtures. Investigators concluded that the improved compaction was likely due to a greater contribution from mobilized binder under the heating and mixing conditions. As RAP content increased, the amount of effective binder also increased, improving lubrication between aggregate particles and reducing resistance to densification.
Adding 6% GNP moderately improved compaction and reduced gyration demand, although the benefits diminished at lower compaction temperatures. Lowering the compaction temperature from 135°C to 115°C had little impact, but reducing the temperature further to 95°C significantly increased gyration requirements. These findings suggest that adding GNP could improve compactability and may allow for some reduction in heating and compaction temperatures.
Low-temperature semi-circular bend and bending beam rheometer testing showed that RAP mixtures had fracture energy comparable to the virgin mixture and generally higher fracture toughness and flexural strength. Within the range of 25% to 50% RAP, increased RAP content did not result in significant differences in low-temperature creep or strength behavior.
“These results provide promising evidence for potentially increasing the use of RAP materials, but more work is needed to implement it for use in the field,” said Eddie Johnson, Researcher, MnDOT Office of Materials and Road Research.
Overall, the findings demonstrated that RAP mixtures prepared under appropriate laboratory conditions can achieve satisfactory compactability and low-temperature performance. However, replicating these preparation conditions in the field may be challenging and costly.
What’s Next?
While project findings support the continued use of RAP mixtures, additional research could further improve understanding of RAP performance, including:
- Quantifying binder activation based on RAP source, heating temperature, mixing procedure and mixing duration.
- Evaluating the effect of the RAP heating process on binder mobilization and compaction performance.
- Conducting field validation of findings from this project, particularly the improved compactability with higher RAP contents and the benefit of adding GNP.
More Information
New Project: Using Satellite Technology to Monitor Ground Deformations Adjacent to Roads
Geohazards generated by ground movements (e.g., landslides, subsidence, sink holes, etc.) cause substantial damage and interruptions to Minnesota’s highway network. Reactive monitoring approaches and borehole-based instrument sensing both have limited spatial coverage and are limited to sites already known to be in distress. This research explores the establishment of continuous satellite-based InSAR monitoring of ground deformations adjacent to roads on a broad geographic scale that would enable detection of pending hazards before they develop into large failures.
This warning system will combine data from high spatial resolution InSAR measurements, optical remote sensing data, and deep learning algorithms to automatically detect and continuously monitor deformations across large spatial regions. The research team will create MnDOT training modules to demonstrate the utility of the deformation data and automated warning system.
InSAR monitoring is expected to improve the safety and reliability of Minnesota’s transportation system and reduce costs and delays associated with emergency repairs. It would also support the state’s geotechnical asset management program by assessing the feasibility of InSAR for tracking performance of geotechnical assets (e.g. retaining walls, slopes, pavement foundations, etc.).
“This research project will help us determine if InSAR technology is ready for prime time for transportation agencies as a remote sensing tool to track performance of assets,“ said Raul Velasquez, geomechanics research & deployment engineer at MnDOT’s Office of Materials and Road Research.
The Objectives:
- Develop an automated warning system that can alert MnDOT staff of areas where abnormal ground deformation (e.g., landslides, subsidence, and sinkholes) is occurring along Minnesota interstate highways, allowing them to proactively intervene.
- Assist MnDOT in continuing to build its geotechnical asset management program by assessing the feasibility of InSAR for tracking performance of geotechnical assets such as retaining walls, slopes, and pavement foundations.
Project Details
- Start Date: 05/16/2025
- Estimated Completion Date: 08/31/2027
- Funding: MnDOT
- Principal Investigator: Ali Khosravi
- Co-Principal Investigators: Anand Puppala, Jack Montgomery
- Technical Liaison: Raul Velasquez
Details of the research study work plan and timeline are subject to change.
To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.
CTS Webinar: Infrastructure Materials and Performance
Tuesday, April 21, 2026
noon–1:30 p.m. CDT, Virtual
About the Event
Understanding how infrastructure materials perform over time is critical to making informed design, construction, and maintenance decisions. This webinar will feature two recent University of Minnesota research efforts that examined the real-world performance of commonly used transportation infrastructure materials.
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Assessing Recycled Pavement for Use in Road Design
Cold recycling road pavement materials into new road construction is a cost-effective and sustainable practice. However, the properties of these materials must be characterized to adequately design pavement structures. This project developed a framework and tool for transportation agencies to estimate the key material properties of cold recycled materials incorporated into road designs.
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Crossroads 