Road Tests
This content originally published in the Winter 2024 print edition of NAPA Quarterly. Subscribe here.
Test sections in North Dakota to provide real-world results for balanced mix designs.
BY CHUCK MACDONALD, Contributor
It can be tricky business to predict how to build long-lasting pavements. Traffic loads, trucking numbers, resistance to cracking, subgrade conditions, and weather all play a part. Most agencies and companies do tests and hope for accurate predictions on how the roads will last over the decades. Balanced mix design (BMD) performance tests like the Hamburg Wheel Tracker and the Indirect Tensile Cracking Test (Ideal-CT) are used frequently to replicate road conditions over time.
The National Center for Asphalt Technology (NCAT) has provided reliable results based on real-world conditions at its test track in Auburn, Ala.
The North Dakota Department of Transportation (NDDOT) decided to take NCAT’s model and subject roads to the harsh conditions in the northern United States. NDDOT is partnering with Border States Paving out of Fargo to build eight test sections, two miles apiece. Each test section will have a different mix proportion designed to have cracking and rutting test results that are variable.
In Summer 2024, the Border States team worked to rebuild ND 14, located about 20 miles from Bismarck, the state capital. The route carries vehicle and truck traffic traveling from I-94 north to Canada. NDDOT has endeavored to use the rebuilt road as the ‘control’ part of the experiment, with the different BMD field verification sections as the variables. The paving project begins at I-94 and stretches north for 21 miles. The full road extends about 175 miles to the Canadian border.
The various mix designs were produced out of the company’s portable asphalt plant located near the project.
The project will use Superpave with a softer binder, PG 58H-34 and PG 58S-28. The various mixes will contend with the state’s extreme weather conditions. The region frequently sees temperatures reach 100° in the summer and temps can plunge to -40° in the winter. This summer, the area near the paving site experienced intense rains with flooding at levels expected only once every 100 years. This flooding followed last summer’s near-drought conditions.
“We have used a disc-shaped compact tension test to measure thermal cracking in a freezing environment,” said Tyler Wollmuth, PE, NDDOT Assistant Materials Engineer and the main mover behind the project. “We run cracking tests at -24° C and -18° C. Still, there is nothing like a live test to see performance under real conditions.”

State transportation agencies in surrounding states are taking a keen interest in the project.
“Highway 14 is not a test track, so we can’t alter the traffic,” said Wollmuth. “There are some gravel pits along that road and farms. Many people use it as a bypass around Bismark or as an alternative to Highway 83. The road will reflect real-world conditions.”
Four of the test sections will use polymer-modified asphalt and four will not. Two of the eight sections will include 15% RAP in the mix. The aggregate will be the same for all the test sections; only the binder content will vary.
“We will probably not see much difference in the sections over the first couple of years,” said Wollmuth. “Within five years, we should see enough variability to make some assumptions. We don’t have much of an issue with rutting here; we are more concerned with cracking.
“We have learned a lot from NCAT in our interactions with them,” said Wollmuth. “Our objective is to be able to build roads for our state that will perform better.”
PAVING THE WAY FOR RESEARCH
Border States CEO Korey Bender and his team handled the paving on the 100,000-ton job. Border States worked closely with Bryce Wuori at PaveWise for statistical information and data and to help establish rolling patterns for each section.
The construction team widened the road and performed a 10-inch full-depth reclamation for the project, which included cement stabilization. The top two layers included a Superpave layer, then 2 inches of the various BMD mixes. The paving team used three different types of aggregate including 5/8″ rock, 3/16″ air-separated crusher dust, and natural sand in the mixes.

No rejuvenators or additives were used.
Workers paved the final test sections with the various BMD mixes during September. Funding for the project came from NDDOT.
Border States workers used a traditional paving train for the work. The paving team used belly dump trucks for depositing the asphalt in windrows feeding the paver with a pick-up machine. RDO and Wirtgen America provided a semi-autonomous roller for part of the field compaction work.
“As somebody who loves asphalt, I think this has been an exciting project to work on,” said Bender. “This was a complex job already, but the BMD facet added even more complexity. I believe this is an opportunity to move the industry forward in building long-lasting pavements.”
As the test sections were being constructed, samples of asphalt were taken at the paver and tested for cracking and rutting performance by NCAT in their mobile lab and by NDDOT in their materials lab in Bismarck. Extra materials will also be sent to the NCAT lab in Auburn for further testing and evaluation. Early testing results indicate that the sections will have plenty of rutting and cracking variability.
NDDOT will continue to monitor these sections to see how traditional test results compare to real-world wear-and-tear.