When asphalt pavements face extreme cold, freeze-thaw cycles, and aggressive snow plow operations, the standard preservation playbook developed in warmer climates may not apply. The National Center for Asphalt Technology (NCAT), under Auburn University and the National Asphalt Pavement Association, recognized this gap and partnered with the Minnesota Department of Transportation (MnDOT) to study pavement preservation in one of the coldest regions of the United States. The resulting test strips in Mille Lacs County, Minnesota, represent a landmark effort to quantify how different preservation treatments perform when temperatures drop to minus-30 degrees Fahrenheit for days at a time. Understanding how cold weather affects paving materials is essential for contractors working in northern climates, much like understanding How Climate Affects Concrete Hot Weather Cold Weather and wind effects is critical for quality outcomes in any paving operation.
Why Cold Climates Demand Different Preservation Strategies
Northern pavements contend with mechanical damage from ice expansion, thermal contraction cracking, and the abrasive action of snow plows. These stresses are fundamentally different from the heat and oxidation that dominate pavement deterioration in southern climates.
The Freeze-Thaw Cycle and Thermal Cracking
When temperatures drop below freezing, the ground and asphalt contract at different rates, creating tensile stresses that crack the pavement. The freeze-thaw cycle compounds the problem:
- Water enters existing cracks and surface voids during warmer periods.
- Temperatures drop below freezing, and the water expands by approximately 9 percent as it turns to ice.
- Ice expansion widens existing cracks and creates new ones.
- The cycle repeats with each freeze-thaw event, progressively deepening the damage.
In central Minnesota, this cycle can repeat dozens of times per winter. Deicing salts compound the problem by keeping pavements wet at colder temperatures, increasing the number of freeze-thaw cycles the surface experiences.
Snow Plow Damage and Infrastructure Funding
Minnesota snow plows operate without plow shoes, meaning the metal blade scrapes directly against the pavement surface. Over years of plowing, this wears away the asphalt surface, particularly in wheel-path areas. This mechanical abrasion creates a damage profile not seen in warmer climates where plowing is rare or nonexistent.
Transportation agencies across the northern United States must maintain roads through harsh winters with budgets that are often shrinking. The solution identified by the NCAT-MnDOT partnership is pavement preservation through thinlays: asphalt overlays of one inch or less, typically three-quarters of an inch thick. Thinlays can extend a road’s service life before major reconstruction becomes necessary, allowing managers to stretch limited funding further.
Test Strip Design and Research Objectives
In the summer of 2016, NCAT and MnDOT constructed 13 hot mix test sections in Mille Lacs County, Minnesota, mirroring identical sections at the NCAT Pavement Test Track in Auburn, Alabama. This parallel design allows direct comparison of the same treatments in fundamentally different climates.
Location and Traffic Conditions
The project includes two road types representing extremes of traffic loading:
- Low-volume route CR-8 near Pease and Milaca, carrying approximately 1,000 vehicles per day, reflecting rural collector roads common across northern states.
- High-volume route US-169 carrying up to 25,000 vehicles per day, representing a major arterial highway where traffic loading and speed compound cold-weather stresses.
Each test strip is 528 feet long (one-tenth of a mile). The monitoring period spans three to five years, with pretreatment conditions documented and ongoing mapping of surface distress.
Research Objectives and Mix Designs
The partnership’s objectives are: quantify the life-extending benefit of preservation treatments in a northern climate, compare performance data between identical treatments in Alabama and Minnesota, evaluate thermal cracking and snow plow damage, and develop performance curves for objective agency decision-making.
The 13 test sections include a variety of asphalt mixture types:
| Mixture Type | Key Characteristics | Intended Application |
|---|---|---|
| Ultra-Thin Bonded Wearing Course (UTBWC) | Thin layer with polymer-modified emulsion bond | Rapid surface treatment with high skid resistance |
| Asphalt Rubber Binder (ARB) | Crumb rubber modified binder for flexibility | Crack-resistant surface in cold climates |
| Open-Graded Friction Course (OGFC) | Porous mix design that drains water | Reduced splash and improved friction in wet conditions |
| High-Modulus Asphalt (HiMA) | Stiffer binder for improved rutting resistance | High-volume road applications |
| High RAP-RAS with Rejuvenator | Recycled material with Delta S plant-based rejuvenator | Sustainable mix with improved crack resistance |
Each mix was produced in 32-ton batches by Hardrives Inc. using their 350-ton asphalt plant. Despite haul distances of up to 45 minutes, mix temperatures at placement ranged between 246 and 258 degrees Fahrenheit.
Equipment, Materials, and Construction Methods
Equipment manufacturers, contractors, and material suppliers donated time, equipment, and expertise to construct the test strips. The project required a crew of 16 from East Alabama Paving of Opelika, Alabama, working alongside local Minnesota contractors.
The Roadtec SP-200e Spray Paver
Madden Contracting Company shipped its Roadtec SP-200e Spray Paver from Louisiana to Minnesota for the project. This specialized paver applies the tack coat and asphalt mat in a single pass, offering distinct advantages:
- No trucks or paver tracks contaminate the cleaned, sprayed road surface.
- No vehicular traffic picks up the tack coat in wheel rut areas because emulsion is sprayed just inches in front of the augers.
- Hot asphalt immediately steams water out of the emulsion, creating a rapid, strong bond between the new surface and existing pavement.
- The shot rate can be varied based on project needs, and spray width matches the asphalt placement precisely.
Astech Corp of St. Cloud donated its SB2500 Shuttle Buggy to feed the Spray Paver during the hot mix test session. As a pavement preservation company working in Minnesota and surrounding states, President Bruce Batzer recognized that his firm would benefit directly from the research.
Rolling, Compaction, and Rejuvenating Additives
Sakai America contributed two double-drum rollers with on-site operator guidance. The SW 770HF and SW 654 rollers provided final compaction of the new asphalt mats. Caterpillar donated a rubber-tired CW 34 wheel roller suited to the thinlay applications. Collaborative Aggregates sponsored a Delta S applied research section at both climate locations. Delta S is a plant-based rejuvenator used in high RAP-RAS content mix designs to restore aged binder properties and prevent premature cracking.
Implications for Agencies and Contractors
The cold-climate test strips represent a significant step forward in pavement preservation science, offering practical guidance for transportation agencies and contractors alike.
Data-Driven Preservation Decisions
As Buzz Powell, assistant director at NCAT, explained, the goal is to quantify the life-extending benefit of each treatment. Once quantified, agencies can make decisions based on life-cycle cost scenarios local to their jurisdiction. The performance curves from the southern climate, combined with the regional shift observed in the north, provide objective data to deliver the best product at the lowest cost to taxpayers.
Approximately 19 states are sponsoring these projects, with more than half a dozen from northern states. The findings reach far beyond Minnesota, providing guidance on thermal cracking and snow plow damage that has not been available previously because those conditions are unique to extreme northern climates.
Practical Guidance for Contractors
Several lessons from the NCAT-MnDOT project apply directly to everyday contracting operations:
- Thinlay technology works when properly specified. Mats of three-quarters of an inch to one inch can extend road life significantly. The key is matching mix design to site-specific traffic and climate conditions.
- Bond quality determines long-term performance. The bond between the thinlay and existing surface is critical in cold climates where freeze-thaw cycles can delaminate poorly bonded layers. Single-pass spray pavers offer the highest bond quality.
- Rejuvenators extend recycled mix life in cold weather. The Delta S plant-based chemistry demonstrates that high RAP-RAS mixes can perform well in freezing conditions when the binder is properly restored.
- Micromilling before thinlay placement improves uniformity. Milling to maintain crown, grade, and cross slope before placing the thinlay ensures a uniform surface that performs predictably over time.
For guidance on equipping teams for winter operations, see Out in the Cold Essential Gear and Strategies for cold-weather construction.
Life-Cycle Cost Benefits
Jeff Brunner, Pavement Research Director for MnDOT, noted that better treatments mean longer-lasting pavements, saving money and reducing disruption to the traveling public. Identifying which preservation treatments provide the best performance-to-cost ratio in cold climates gives agencies the tools to stretch infrastructure dollars further. Similar research into cold-climate building systems, such as the work on Do Heat Pumps Work in Cold Climates a and Do Heat Pumps Work in Cold Climates a, demonstrates the same principle: climate-specific design produces better outcomes than one-size-fits-all solutions.
Conclusion
The NCAT-MnDOT cold-weather test strip project is a milestone in pavement preservation research. For the first time, identical treatments are being evaluated in both a temperate southern climate and an extreme northern climate, providing agencies with data to make informed, cost-effective decisions. The 13 test sections in Mille Lacs County, subjected to freeze-thaw cycles, minus-30-degree temperatures, and direct snow plow contact, will deliver performance data that defines best practices for cold-weather pavement preservation for years to come.
The collaboration between NCAT, MnDOT, equipment manufacturers, contractors, and material suppliers demonstrates what the industry can achieve through public-private partnership. The ultimate beneficiaries are taxpayers who get longer-lasting roads and the traveling public who experience fewer construction delays and safer driving surfaces throughout the year.