Better Roads Staff
Working 15 feet wide, a Blaw-Knox PF-3200 paver equipped with a Carlson Easy IV screed placed the asphalt. The contractor used a Blaw-Knox contact ski on the centerline and a contact-on-mat reference ski.
The breakdown roller was a Sakai SW-800 roller working 66 inches wide and making three passes. The average warm mix temperature at the breakdown roller ran about 30 degrees cooler than the hot mix temperature – 245 degrees F vs. 275 degrees F, respectively. A 54-inch-wide Bomag BW 138AD roller handled finish rolling work. The finish roller made five passes, and warm mix temperature there averaged 130 degrees F compared to 135 degrees F for the hot mix.
Northeast Asphalt released an official report of results on the project and reported several advantages for warm mix using the Akzo Nobel Rediset additive:
• The average burner fuel savings reached 10 to 12 percent, operating at an average of 275 degrees F.
• The asphalt cement mixture is workable with the additive and RAP incorporated into the asphalt cement mixture.
• The asphalt could be compacted at lower temperatures
• The additive offers the potential to extend haul distances beyond what is possible with hot mix.
“There were no clear disadvantages found in regards to using the Akzo-Nobel Rediset LQ-1106 warm-mix additive,” the report states.
“Warm mix widens the temperature window at which you can compact the asphalt,” says Van Beek. “The asphalt is more workable, and easy to construct. We changed up our rolling pattern somewhat with the warm mix. With warm mix we backed off the breakdown roller because the temperatures were quite a bit lower. Then on the hot mix we worked up closer to the paver.
“We experimented with putting a rubber-tired roller between the hot roller and the cold roller,” says Van Beek. “But then we found that we actually got a better ride by putting the rubber tired roller behind the cold roller.” Van Beek reported an absence of smoke and fumes with warm mix.
Taking out the cracks
Back in the mid-‘90s some road managers would prescribe sawing and sealing joints in asphalt pavements, in similar fashion to concrete pavements. It didn’t work out very well, as the Minnesota Department of Transportation (MnDOT) found on Highway 59 in Stevens County.
“The theory was that if they sawed and sealed joints in the bituminous pavement, it would control the cracking,” says Brad Cegla, an MnDOT construction engineer. “But because of the sawing and sealing on Highway 59, those joints faulted over the years. You got a bumpy pavement.”
To repair a 13-mile stretch of the two-lane road, MnDOT required milling to a depth of 1.5 inches, cold-in-place recycling to a depth of 3 inches, and two lifts of hot-mix overlays, each 1.5-inch thick. The initial milling assured the state that the height of the final roadway would only rise 1.5 inches above the original grade – an important factor to keep crossings and entrances close to the existing height.
Cegla says the state chose cold recycling because it would take out the faulted joints and prevent reflective cracking later on. “The thinking was to break up that reflective cracking from below, and provide a recycled layer between the original pavement and our new overlay,” says Cegla.
Anderson Brothers Construction of Brainerd, Minn., won a $3.5 million contract with MnDOT to rehabilitate the road. After the initial milling, a subcontractor, Midstate Reclamation of Lakeville, Minn., swung into action with its cold-in-place recycling train.
“Our crew managed to complete 2.5 to 3 miles each day, working 10-hour days,” says Andrew Dauk, Midstate’s project manager. “The specification for cold-in-place recycling called for temperatures to be 50 degrees and rising. We figured our production was pretty impressive, considering that average overnight lows for that time of year are in the low-40s and working daylight hours are at their lowest.”
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