It may very well be the smoothest 10 mi. (16 km) of interstate highway in the state of Montana and maybe even in North America. Heck, it might be the smoothest chunk of highway on the globe, if you talk with those involved.
A recently renovated 10-mi. section of I-90, starting in Alberton, Mont., which is located on the western part of the state near the Idaho border, and stretching east, received sterling commendations, shattered target IRI scores, and earned the general contractor $605,000 in quality bonuses. It even won the 2014 MCA Excellence Award for Best Paving Smoothness from the Montana Contractors Association.
“Our crew, subcontractors, and the Montana Department of Transportation [MDT] inspectors all worked seamlessly together giving us the efficiency, thoroughness and quality results we were after,” said Lance Streeter, general superintendent with Knife River Corporation’s Western Montana Division, headquartered in Bismarck, N.D. “This was a two-year project that we finished in one construction season.”
Knife River Corporation was the general contractor on the $15.5 million I-90 renovation. The company has 5,000 employees during peak season and operates in 18 states with physical locations in 14 of them. It is the country’s 10th largest aggregate producer and the 5th-largest U.S. producer of sand and gravel. The company had eight employees assigned to the road project.
The I-90 project commenced on June 10 with Knife River’s subcontractor Industrial Builders Inc., Bismarck, N.D., performing the shoulder-to-shoulder rotomilling of the road to three-tenths of a foot, with the milled material converted to reclaimed asphalt pavement (RAP). The drive lane and passing lane were milled out an additional three-tenths for a total of six-tenths of a foot.
As Industrial Builders began completing the 40 lane miles of milling, Knife River could begin paving.
“When we first looked at this project I knew we had to be aggressive in our work schedule and that we had to achieve consistent smoothness with each lift that we placed,” Streeter said. “The payment incentives that MDT offered were very attractive and within our capabilities to achieve.”
The bonus incentives offered by MDT were based on achieving paved finished surfaces with favorable International Roughness Index (IRI) scores:
• 45 — 55 IRI was acceptable — no bonus, no penalty
• 35 — 44 IRI earned up to 24 percent bonus, based on a sliding scale
• below 35 IRI earned a 25 percent bonus
“I knew that in order to achieve a low IRI index throughout the job that we needed continuous paving with thoroughly mixed HMA at the right temperature,” said Streeter. “I knew that in order to achieve that we’d need to use a Shuttle Buggy.”
Knife River owns three Roadtec SB-2500e/ex Shuttle Buggy material transfer vehicles (MTV) that are designed to store and transfer hot-mixed asphalt material to a paver to enable continuous paving production. An anti-segregation auger remixes materials just before delivery to the asphalt paver.
“I was a part of our decision to purchase our first Shuttle Buggy MTV in 1998, so I knew how critical this machine would be to maximizing the performance of our asphalt paver; plus, we have the same operator and mechanic from back then who know the machine inside out ” Streeter said. “The Shuttle Buggy was instrumental in ensuring continuous paving and it reduced our trucking costs since the trucks could dump their loads and return to the plant, which was located about 23 to 28 miles away.”
Streeter continued, “When you look at temperature change and segregation issues that can occur during a 30-minute haul, it’s easy to see how the Shuttle Buggy helps. With its 25-ton surge capacity we had plenty of mix to feed the paver and keep it continuously productive. This meant our belly dump train could unload and leave right away.”
Knife River used a two-dump-truck train for asphalt hauling. The lead belly dump had a 26- to 28-ton (23.6 to 25 t) capacity and the connected pup had a 12- to 14-ton capacity. The Shuttle Buggy used a windrow pickup head to add the hauled HMA to its dump hopper. The Roadtec SB-2500e/ex is powered by a 300 hp Cummins QSL 9 engine.
The Montana I-90 rehab project required a total of 165,000 tons (149,685 t) of HMA with approximately one third of that being RAP. Knife River placed three lifts. The bottom lift was three-tenths thick and the top two layers were each 15-hundredths.
“The Shuttle Buggy was key to ensuring our quality on each lift,” said Streeter. “It was interesting that as our MDT inspectors began to see the quality we were achieving we started seeing more and more visits from other MDT officials outside of our team — they were very interested to learn how the MTV was helping us.”
The project required cooperation and coordination to maintain uninterrupted paving. In addition to the steady delivery of HMA from the asphalt plant, there was the removal and replacement of 60,000 ft. (18,288 m) of guardrails.
“Our sub, Mountain West Holding Company, based in Missoula, Montana, had all six of their punch trucks working,” Streeter said. “They did an incredible job of pulling guard rails in front of the paver and then replacing them after the paver — it was poetry in motion.”
The Montana I-90 project, which started in June, was completed Oct. 28 — a full year ahead of schedule. In addition to an early completion, Knife River Corporation also achieved an average IRI index score of 29, which gave the company the highest incentive payment for finished pavement smoothness. For its efforts, Knife River earned $605,000 in bonuses.
“This project was a totally coordinated effort among everyone connected with the project,” said Streeter. “We created a smooth, very rideable, surface — probably among the best I’ve ever seen.”
In looking back at the project, Streeter credits the Shuttle Buggy for helping them achieve the quality of paving, and for production savings.
“With our Roadtec Shuttle Buggy, I estimate that we easily saved $165,000 in our trucking costs alone,” stated Streeter. “There were no delays. Our belly dump train could unload and leave right away.”
The quick turnaround of the haul trucks helped maintain the aggressive production pace the Knife River set. Early in the day, Knife River would pave at a rate of 450 ton (408 t) per hour and slow the pace down to 350 ton (317.5 t) per hour toward the end of the day because they were outstripping the asphalt plant’s production.
“The key to our success on this job was the ability to keep our paver continuously paving with homogenously mixed HMA at the right temperature,” Streeter concluded. “The Shuttle Buggy made it possible. It gave us the production consistency that made the difference to this 10-mi. stretch of I-90 between the Alberton Interchange and the Huson Interchange.”
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