Like most state departments of transportation, North Dakota DOT takes a systematic approach to maintaining the quality of its road network. Through its Pavement Management System (PMS), NDDOT's central office inspectors drive every road in its network once a year to assess the "pavement condition value" of road structures, using technology to analyze the ride smoothness, the extent of rutting, and photo images to document surface conditions.
The information is then forwarded to district offices to help district engineers evaluate the projects they would like to address in the coming season. District offices then forward their "wish list" to the central office for further analysis based on the classification of the roadway, the volume of traffic it carries, and the importance the road plays in overall statewide transportation's system.
According to Scott Zainhofsky, NDDOT planning/programming engineer, the road agency does not operate by focusing on the worst roads first.
"We are working to provide a statewide level of service based on what the public wants," Zainhofsky says.
To do that, preserving and maintaining good roads is a priority because it provides the best value to taxpayers.
District engineers provide a list of preservation and reconstruction projects they would like to address and NDDOT's central office advises them on how much funding they will receive. Preventive maintenance and preservation projects have and continue to allow district offices to maximize the funding they receive by extending the service life of good roads.
Typically, a new hot mix asphalt road will receive a chip seal application two to three years after it's been constructed. That's generally the first line of defense or offense in extending the life of a NDDOT asphalt road.
The road agency has tried to go longer than two to three years before applying its first preservation treatment, but North Dakota weather is brutal - 100 degree summers and -20 degree winters, accelerating surfacing deterioration.
Recent work on a section of Interstate 29 north of Fargo illustrates how NDDOT uses preservation to continue maintaining the serviceability of a good road structure that requires more than just a chip seal solution.
Omaha, NE-based Monarch Oil Company, a division of Martin Resource Management, was contracted to micro surface a 21-mile stretch of I-29 from the Argusville Interchange to the Blanchard Interchange.
The original 8-inch-thick continuously-reinforced Portland cement concrete interstate was overlaid with hot-mix asphalt in the late 1990s. According to Kevin Gorder, assistant Fargo District engineer, a 3-inch asphalt overlay was specified at the time, with crown and slope corrections resulting in a thicker asphalt overlay on portions of the two 12-foot-wide travel lanes. Several years after that major upgrade, NDDOT's Fargo District invested in a chip seal maintenance application.
Since it's a heavily-traveled north/south corridor, supporting freight traffic in and out of Canada, the 10-year-old asphalt overlay was beginning to show signs of rutting, particularly in the right travel lane of both northbound and southbound sections of this stretch of I-29.
Several years ago traffic counts averaged approximately 11,000 vehicles daily, with trucks hauling freight in and out of Canada representing 20% to 25% of that volume. NDDOT chose micro surfacing as the best solution to fill the ruts and improve the overall safety and ride smoothness of road.
The International Slurry Surfacing Association states that "micro surfacing is recognized not only as the most cost-effective way to treat the surface wheel-rutting problem, but also a variety of other road surface problems."
Research gathered by ISSA also supports applications of micro surfacing capable of filling wheel ruts up to 1 1/2 inches deep when the pavement has stabilized and is not subject to plastic deformation.
A micro surfacing application will generally extend a good road's serviceability for another seven years or so before an additional maintenance/preservation treatment is required.
Monarch executes the project
According to Steve Walenz, Monarch general manager, the project was originally let out for bid as two separate projects (northbound and southbound) and eventually combined and awarded in 2008. Due to weather and construction delays, the combined project was moved to the 2009 construction season.
The project called for a micro surfacing Type III (-3/8-inch aggregate) scratch coat to fill the ruts on the right travel lanes and a second micro surfacing Type III wearing course over both travel lanes, with a fog seal emulsion application on the adjacent shoulder asphalt.
"Rather than using individual rut boxes to apply the scratch coat, we used a 10-foot-wide box to provide a more consistent and level plane that is otherwise difficult to achieve with separate rut box passes over each rut," Walenz explains. "We had approximately 80 lane miles to pave with the final wearing course after we addressed the ruts with the scratch course on the right travel lanes."
Using a Bergkamp M1 paver, Monarch's micro surfacing paving crew of 25 completed the project in approximately 30 days.
"The road was in pretty good shape and only required some minor milling of some cracks where pavements were pushing together and bulging upward," explains Justin Arnold, construction manager overseeing the project.
The real challenge for Monarch was maintaining the stockpile of Type III aggregate it had staged in Cass County in 2008.
"Because weather conditions not only delayed this project but some of our other projects, we were not able to complete the work in 2008 as intended," Walenz explains. "That produced the additional challenge of maintaining the stockpile so the gradation stayed in tack, especially since the bottom two feet of the pile was under water during the spring flooding (2009 Red River)."
The only other unplanned challenge that had to be addressed once the project got underway was in removing the existing centerline stripe, which consisted of a material NDDOT did not think the micro surfacing application would adhere to.
"We had to make some scheduling adjustments once we got underway to accommodate other subcontractors, but since we produce the CSS (cationic slow-setting) emulsion used in the micro surfacing process, we were able to control when and how much to ship to our staging area in Cass County," Walenz states. "We used seven to eight nurse trucks to supply the paver since we were operating 20 miles or so from our staging area. We completed all the work within 28-30 days with single-lane closures during the day to apply the treatment and allow it to cure."
The total project required 12,000 tons of the Type III aggregate and 370,000 gallons of CSS-1H polymer-modified emulsion to complete the micro surfacing work, and approximately 63,000 gallons of HFMS-2 emulsified liquid asphalt to fog seal the 9.5-foot-wide outside shoulder and 3-foot-wide inside shoulder.
For NDDOT, the micro surfacing preservation approach used on I-29 provided the most cost-effective solution to address rutting issues, while delivering a safe and smooth ride for motorists who rely on that vital corridor. It's just one of many tools the road agency uses to keep good roads in good condition.