Warm-Mix Asphalt Simplifies Wisconsin Highway Job

By Mike Larson, Editor | September 28, 2010

Payne & Dolan, Inc., Waukesha, WI, found that warm-mix asphalt was the ideal product when it repaved three miles of two northbound lanes on State Highway 74 near Sussex, WI, just west of Milwaukee.

Owned by the Wisconsin Department of Transportation (WisDOT), the project included milling, pulverizing and repaving the two northbound driving lanes and a shoulder lane from the highway's junction with Capitol Drive, northward to its intersection with County Hwy. K.

It also included lowering and repaving 500 feet of Highway 74's two southbound lanes to create more clearance under the Capitol Drive overpass.

The $1.8-million contract required the project to be completed in 25 working days — with limited work during peak traffic hours.

Warranted Project Gives Contractor More Options

WisDOT let this project as a warranted job with a ride specification, rather than as a traditional bid.

In a traditional bid, the contractor must meet a number of specifications for asphalt mix type, lift thickness, application temperatures, compaction density, and other factors throughout the process. After the job is done and has met all the specifications, WisDOT takes control of the road, and the contractor's responsibility for the job is through.

When a job is bid as a warranted project with ride specification, WisDOT's requirements focus on the end result, rather than the materials and processes used to achieve it.

WisDOT provides inspection of the process and approves the methods used, but the contractor remains responsible for correcting any flaws that show up during the next five years (that's the warranty).

While WisDOT provides the general guidelines of the project including the sub-base preparation and overall thickness of the pavement, the contractor selects the asphalt mix types and layer thicknesses. Payne & Dolan worked in collaboration with WisDOT to use warm-mix asphalt (WMA) for the pavements on STH 74.

Payne & Dolan Project Manager Sam Bilhorn explained, "This road sees lots of heavy truck traffic, and our experience with WMA told us that we could use it to provide an excellent pavement that would meet the specified requirements."

"WMA," continued Bilhorn, "stays workable longer, so we have more time to get the compaction just right for each lift we put down."

The final product was to be further examined for quality, as WisDOT had included a ride quality specification — that is, the completed road would be tested for bumps, roughness and other irregularities that could adversely impact the ride quality felt by the traveling public.

For such a ride-spec job, WisDOT tests the finished pavement by driving a specially equipped vehicle over the completed road at specified speeds while the test vehicle's sensors measure all of the required elements.

Process Begins With Milling

Payne & Dolan began reworking the northbound lanes by using a milling machine to grind off 4-1/2 inches of the 7-inch-deep existing asphalt pavement.

The milled-off asphalt was trucked to a Payne & Dolan processing plant for recycling in future paving projects.

The remaining 2-1/2 inches of asphalt was then pulverized into the top 6 inches of the gravel base, which was then graded and compacted.

Explained Bilhorn, "Since the base course and roadbed were in good condition, they made a good foundation for the new asphalt pavement. We pulverized the bottom 2-1/2 inches of the existing pavement and mixed it into the existing gravel base and then graded for the asphalt pavement. This allowed more material to be reused on site, reducing the amount of existing materials that needed to be removed from the site."

Warm-Mix Asphalt Selected For Pavement

For the new pavement, Payne & Dolan chose to use WMA from one of its production plants in nearby Sussex, WI.

The mix was designed by Payne & Dolan's in-house experts and approved by WisDOT.

According to Payne & Dolan Quality Control Manager Signe Reichelt, hot-mix asphalt (HMA) and WMA are pretty much identical, except that WMA contains just one extra ingredient that enables it to remain pliable at lower temperatures.

Says Reichelt, "The added ingredient keeps the WMA pliable and workable for a longer time than HMA, but it does not change the strength of the final pavement. Within 12 hours after the asphalt has set up, all traces of the added ingredient disappear. After that, you cannot tell whether the asphalt was HMA or WMA."

Adds Reichelt, "Because WMA stays workable at lower temperatures, it is particularly useful at the beginning and end of the paving season."

In addition to providing extended working time, the WMA was also chosen for its environmental friendliness. Says Bilhorn, "Warm-mix asphalt takes less burner fuel to heat the mix and less electricity to run the plant as the material is produced at temperatures 40 to 50 degrees cooler than HMA."

Paving Technique Key To Superior Result

But while WMA gives the paving crew more time to do the job perfectly, paving technique is the real key to a superior pavement.

Says Bilhorn, "How well an asphalt pavement turns out depends on the mix, but even more so on how the asphalt is laid and compacted. How many lifts will you use to achieve the total depth of pavement? What thickness should each layer be? How will each be compacted? How continuous is the paving operation? There are many considerations."

For this job, Payne & Dolan decided to pave each of the two northbound lanes in three lifts totaling 5-1/2 inches — using 16,000 tons of asphalt for the entire project.

The paver on the project was an Ingersoll Rand 3201.

According to Bilhorn, "One of the challenges was completing the paving smoothly in spite of limited working conditions during peak traffic periods. At times we would work through the night in order to get a long, uninterrupted stretch of work done."

Bilhorn says that one key to a superior result was using the Roadtec SB-2500C asphalt transfer device to feed the paver rather than dumping directly from asphalt-delivery trucks into the paving machine. "Whenever the paver stops moving, there's potential to create a bump in the roadway," he says. "Having the trucks deliver into the transfer device, which then feeds the paver by conveyor, eliminates one potential source of bumping and stopping the paver."

For each layer, or lift, Payne & Dolan first paved one lane, then the adjacent one. To be sure the center seam where the two lanes abut knitted together, Payne & Dolan used a joint heater to soften the edge of one lane's pavement, as it laid the pavement for the adjoining lane along side.

The vibratory rollers worked in synch with the paver to make sure each lift was compacted uniformly over its entire width and length.

Payne & Dolan completed re-paving of the northbound lanes and shoulder on time, and the construction efforts resulted in an overall ride incentive to Payne & Dolan from WisDOT.

Short Stretch Of Southbound Lanes Also Part Of Job

The Hwy. 74 contract also included lowering and repaving 500 feet of the two southbound lanes in order to create more headroom under the Capitol Drive overpass.

That part of the job required digging out the existing concrete pavement and base course, grading the road bed lower, then laying new base course and repaving the stretch with new concrete.

Payne & Dolan subcontracted the excavating and grading for that part of the project to Musson Brothers, Inc., Rhinelander, WI, and subcontracted the concrete paving to Trierweiler Construction, Marshfield, WI.

That portion of the project was also completed on time and within spec.