How Two of the Largest Pavement Testing Facilities Are Tackling Hot and Cold Climate Challenges

The world of pavement engineering is defined by a fundamental challenge: what works in a hot, humid climate may fail completely under freezing winter conditions. For decades, state departments of transportation (DOTs) across the United States have relied on research from two of the largest accelerated pavement testing facilities in the world to guide their design specifications. Now, a formalized partnership between the National Center for Asphalt Technology (NCAT) in Alabama and the MnROAD facility in Minnesota is producing groundbreaking parallel experiments that address the full climatic spectrum. This collaboration directly impacts how engineers approach asphalt pavement engineering mix design construction methods rehabilitation strategies and pavement management systems across all climate zones. By testing identical materials under dramatically different conditions, researchers are generating implementable data that benefits DOTs and ultimately thousands of cities and towns nationwide.

The NCAT-MnROAD Partnership: A New Era in Pavement Research

NCAT, headquartered at Auburn University, operates the Pavement Test Track in Opelika, Alabama. MnROAD, owned and operated by the Minnesota Department of Transportation, sits about 40 miles northwest of Minneapolis. These two institutions represent the largest full-scale accelerated pavement testing facilities on the planet, and their newly formalized partnership marks a significant shift in how pavement research is conducted.

In the past, transportation officials in northern states expressed concerns that findings from NCAT experiments were not directly applicable to their colder climates. The partnership directly addresses this limitation by running parallel experiments with identical materials and construction methods at both locations. The climate contrast could hardly be more extreme:

According to Dr. R. Buzz Powell, PE, Assistant Director and Test Track Manager of NCAT, researchers from the two centers have informally collaborated for years through the Transportation Research Board’s Committee on Full-Scale Accelerated Pavement Testing. However, research programs were historically limited to DOTs with similar climates. The new formal agreement changes that paradigm entirely, with funding provided by 19 state DOTs through the national Transportation Pooled Fund that supports the NCAT Pavement Test Track.

Inside the Testing Facilities: Scale and Capabilities

Understanding the scale of these two facilities is essential to appreciating what the partnership can achieve. Each represents a massive investment in infrastructure designed to simulate years of real-world traffic in a compressed timeframe.

NCAT Pavement Test Track in Opelika, Alabama

The NCAT facility consists of a 1.7-mile oval track featuring 46 test sections, each measuring 200 feet in length. Sections are sponsored in three-year cycles by state DOTs, the Federal Highway Administration, and industry partners who bring specific research objectives to their sponsored sections while contributing to shared objectives for the entire track.

Key capabilities include:

• Continuous trafficking by 70-ton tractor trailers over two years
• Simulation of up to 15 years of Interstate traffic loads
• Controlled loading conditions for precise comparative analysis
• Advanced instrumentation for real-time pavement response monitoring

MnROAD Facility Near Minneapolis, Minnesota

MnROAD encompasses a more complex layout that includes three distinct roadway components:

• A 3.5-mile segment of Interstate 94, providing mainline traffic loading under real conditions
• A 3.5-mile bypass for diverting interstate traffic when test sections need to be constructed or evaluated
• A controlled-access 2.5-mile closed-loop low-volume roadway that simulates rural road conditions

The facility contains 50 test cells, each 400 feet in length. Research is sponsored by state DOTs, the Minnesota Local Road Research Board, FHWA, and industry partners. Principal staff includes Ben Worel, Dave Van Deusen, and Chelsea Hanson, supported by MnDOT Materials Research personnel Jerry Geib, Paul Nolan, and Jeff Bruner, who collaborated with Dr. Powell on the pavement preservation test sections.

Cracking Under the Microscope: Validating Laboratory Tests

One of the two primary experiment groups in the NCAT-MnROAD partnership focuses on cracking validation. Cracking in asphalt pavements is widely recognized as the principal indicator of pavement failure. It typically results from fatigue caused by repeated traffic loading, and it manifests in different forms depending on climate and pavement structure.

Types of Pavement Cracking Under Investigation

Dr. Powell explained that the cracking group experiments were designed to identify laboratory test methods that accurately predict cracking in the field. The research targets two distinct cracking mechanisms:

• Near-surface fatigue cracking: This type initiates at or near the pavement surface and propagates downward. It is commonly associated with hot weather conditions where repeated heavy loading causes the upper pavement layers to fail.
• Reflective cracking: This occurs in rehabilitated pavements near the junction with an existing asphalt layer that is already cracked. The crack propagates upward through the new overlay, compromising its structural integrity and allowing moisture infiltration.

Experimental Design: Hot Versus Cold

The beauty of the partnership lies in the experimental design. Hot weather sections were built on the NCAT Pavement Test Track to study near-surface fatigue cracking, while cold weather cells were constructed at the MnROAD facility to investigate low-temperature cracking. At both locations, mixes were selected to incorporate various combinations of recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS), providing a broad range of cracking performance for evaluation.

An array of laboratory tests is being conducted on both lab-produced and plant-produced mixes. The goal is to identify which laboratory tests best predict actual field performance. Reliable cracking tests that can be used during mix design and for quality assurance during production are critically needed to eliminate mixes that lack durability.

With fewer new roads being built today and increasing emphasis on reusing materials milled from existing pavements, the DOT community has growing concerns about premature cracking caused by the brittle and oxidized condition of recycled materials. While incorporating RAP and RAS reduces manufacturing costs by replacing virgin aggregates and some virgin liquid asphalt binder, the potential impact on long-term pavement performance remains a major concern that these experiments aim to resolve.

For additional context on pavement surface treatments and their regulatory background, see Refined Tar Based Pavement Sealers What Pavement Professionals.

Pavement Preservation: Cost-Effective Strategies for Extended Service Life

The second major experiment group focuses on measuring the effectiveness of pavement preservation treatments. These treatments are designed to improve pavement condition and extend service life for both low-traffic and high-traffic roadways. The Federal Highway Administration recognizes these methods as effective strategies for preserving pavements that remain in good condition before the onset of serious damage.

Applying cost-effective treatments at the right time can restore pavements almost to their original condition, postponing costly rehabilitation and reconstruction. The NCAT-MnROAD experiments are quantifying these benefits across different climates and traffic levels.

Treatment Types and Locations

Test sections were built on local roadways near both facilities to evaluate treatments under realistic conditions:

The treatments installed by the contractor East Alabama Paving included:

• Chip seals
• Microsurfacing
• Scrub seals
• Cape seals
• Thin overlays

East Alabama Paving was the same contractor used for the NCAT sections, ensuring that treatments at both facilities were designed and built identically. Dr. Powell traveled to the MnROAD facility in August 2016 to oversee construction and verify consistency.

The Role of Asphalt Rejuvenators in High-RAP Mixes

A particularly notable experiment within the preservation group involved applying a 3/4-inch wearing course inlay of dense-graded hot mix asphalt containing RAP and RAS dosed with an asphalt rejuvenator. The rejuvenator used was Delta S, a plant-based liquid chemistry developed by the Warner Babcock Institute for Green Chemistry and supplied by Collaborative Aggregates LLC.

The application was performed on the northbound slow lane of US Route 169 near Pease, Minnesota. The construction sequence was as follows:

1. Milling out 3/4 inches of existing wearing course from the 400-foot test cell
2. Application of a tack coat of asphalt emulsion at the rate of 0.23 gallons per square yard over the milled surface
3. Manufacturing of the asphalt mix using a portable 350-ton-per-hour Barber Greene drum mix plant owned and operated by Hardrives Inc.
4. Injection of Delta S rejuvenator in line with the liquid asphalt supply, as was done in the Alabama experiments
5. Storage of finished mix in three silos supplied by Dillman Equipment
6. Delivery via haul trucks to a ROADTEC SB-2500 material transfer buggy
7. Paving with a ROADTEC Spray Paver
8. Initial breakdown compaction using a SAKI SW770 HF roller in vibratory mode
9. Finish compaction with a SAKI SW654 static roller

The rollers produced a nuclear density gauge reading of 94 percent for the experimental mix, indicating good compaction quality. Equipment and materials were donated by suppliers: SAKI donated the rollers, Dillman Equipment supplied the silos, and Delta S was donated by Collaborative Aggregates LLC.

The parallel experiments are producing findings directly implementable by a larger base of state DOTs that previously may have had concerns about the applicability of research from facilities operating in a different climate. Field performance data from both cracking and preservation experiments is being monitored with identical automated technologies at both locations, with all data stored in a shared database.

For professionals looking to get the most out of industry events where such innovations are discussed, Maximizing Value At Pavement Maintenance Trade Shows Lessons offers practical guidance. And for a deeper look at the equipment side of pavement removal and preparation, see Tearing Up the Pavement Modern Cold Milling and.

Implications for State DOTs and Municipalities

The broader implications of the NCAT-MnROAD partnership extend well beyond the research community. State DOTs and municipalities that rely on DOT pavement specifications for local roads and streets will benefit from:

• Validated cracking tests that can be used during mix design and quality assurance, reducing the risk of premature pavement failure
• Quantified performance data on preservation treatments across different climates, enabling more informed budget allocation
• Guidance on optimal RAP and RAS content levels, balancing cost savings with long-term durability
• Data-driven rejuvenator dosing recommendations for high-recycled-content mixes
• Climatically appropriate pavement design strategies that account for local conditions

As the findings from these parallel experiments emerge, they promise to reshape pavement engineering practices across the United States, delivering safer, more economical, and longer-lasting roadways from the Gulf Coast to the Great Lakes.