The base lift was compacted to 2 in. deep and was followed by a 1 1/2-in. friction course. The road was paved in two 14-ft. passes, resulting in a 12-ft. driving lane with 2-ft. paved shoulder each way, flanked by 4-ft. gravel shoulders. A total of 20,000 tons of WMA was placed on the just-under five-mile-long project.
For the project, the initial cost of the WMA PG 58-28 was $3 per ton less than the traditional HMA PG 58-34 binder. More data and time are required for long-term performance answers, but the initial indicators are positive.
The WMA test also permitted the county to boost the percentage of RAP used in the mix. RAP that had been removed from the pavement the year earlier was screened and crushed, and stockpiled during the winter prior to reuse in the warm mix.
"In Minnesota, the type of binder determines the maximum RAP that can be used, and because we are using PG 58-28 oil -- non-polymer modified -- we can use up to 30% RAP," says Wayne Dosh, senior engineering technician, Crow Wing County Highway Department. "If it were polymer modified, we would be restricted to 20% RAP. That was one of the benefits of using the warm-mix additive, as we were able to bump up the RAP another 10%, with further savings."
Warm mix was being delivered by bottom-dump trailers from a portable plant minutes away, and placed by an Ingersoll-Rand/Blaw-Knox PF-3200 paver. The paver was fed by a Cedarapids windrow elevator.
Breakdown rolling was done by a Caterpillar CB-534D vibratory steel tandem roller using three passes. A Caterpillar PS-360B pneumatic roller made seven passes in the intermediate spot. And the finish roller -- an Ingersoll-Rand DD-110HF articulated double-drum compactor -- made five passes in static mode.
Because WMA is not as dependent as HMA on heat to provide the workability needed to achieve density, the county may be able to extend its paving season, which is limited in the northern tier of states.
"From what I've seen, WMA will be an excellent way to extend the paving season," Dosh says. "We typically are not supposed to place asphalt after September 15, in the northern part of the state. And due to weight restrictions following the winter thaw, we can't start hauling heavy loads like asphalt from the middle to the end of May, depending on the kind of winter we've had. If there's been a long, cold winter, it might be the first of June before we can pave. [With WMA}, we are looking at a paving season of 120 days -- longer if there is a warm fall."
Greenville Paving puts shingles in the mix
Just over two years ago, James Ross, asphalt/quality control manager at Greenville Paving & Contracting Inc., Greenville, NC, returned from a recycling conference inspired by the information presented on recycled asphalt shingles (RAS). "At the time, AC binder prices were in the $700/ton range," he notes. "How do we save money and still put out a quality product? I felt RAS was the answer."
Greenville Paving & Contracting convinced the North Carolina Department of Transportation (NCDOT) to test the RAS mix on the US-258 resurfacing project, which consisted of nine miles of widening, resurfacing and shoulder reconstruction on two sections. Mixes used included 7,311 tons of B25.0B (base), 23,347 tons of I-19.0B (binder) and 13,721 ton of S9.5B (surface). Only the S9.5B surface mix had the tear-off shingles in its design.
The base and binder mixes were placed in May and June. Provisional approval was given on the tear-off shingle and RAP blend S9.5B surface mix design in late July. By mid-August, approximately 8,000 tons of S9.5B surface mix with recycled tear-off shingles and RAP was placed. The mat was laid at a rate of 168 lbs. per sq. yd. at 1 1/2 in. Equipment used included a Caterpillar AD1000 paver and two 634D rollers, plus a Roadtec material transfer vehicle.
Ross says they have seen improvements in items such as rutting and volumetric properties over traditional mixes. Another important improvement is less compactive effort.
"Density compaction on a RS9.5B mix is 92% per NCDOT specifications," says Justin Ross, certified roadway and density technician for Greenville Paving. "While using the mix that contained the tear-off shingles, product densities were running on average 93.2% with less compaction effort than the same mix type without the shingles."