Setting the Smoothness Standard

When the National Asphalt Pavement Association heads to The Big Island of Hawaii in February for its 50th Annual Convention, attendees will travel one of the smoothest roads on their way to the convention hotel thanks to the technology and craftsmanship Jas. W. Glover Construction employed in resurfacing a 21.5-mile stretch of the Queen Kaahumanu Highway.

The Hawaii DOT project required profile milling and fresh HMA overlay to achieve an average International Roughness Index of 90 inches per lane mile, with no individual areas of the surface having a deviation (bump or dip) exceeding four-tenths of an inch in 25 feet. Well, Glover not only met the smoothness specification, the asphalt contractor far exceeded the specification with a smoothness rating of well under 60 inches per lane mile.

Prior to beginning work on the project in April, Glover took profile readings of the existing road surface and recorded average IRI smoothness deviations of 180 to 200 inches per lane mile. All the milling crews and paving crews had to do was reduce those deviations by 50 percent in order to qualify for smoothness incentives. But unlike other paving projects, where the contractor would typically put down an intermediate course and a surface course to obtain the smoothest ride possible, this project called for only a 1 1/2-inch surface overlay on the two 12-foot-wide travel lanes. The contractor also had to construct 10-foot-wide shoulder lanes that were used as travel lanes during construction.

Michael Park, paving superintendent for Glover, says that "with only one chance to meet the IRI smoothness specs with an overlay, we had to rely on the milling process to remove most of the existing surface deviations." Hawaii's DOT just implemented the IRI smoothness specifications two years ago, and the Queen Kaahumanu Highway resurfacing project was the first major project that would be put to the test. It was also the largest road project Glover has undertaken, and it required a considerable investment in new equipment to achieve smoothness requirements and the completion deadline of September 1.

Milling operation

Using a Roadtec RX60 milling machine equipped with a Topcon System 5 automated laser leveling device that uses three electric eyes to calculate the average highs and lows of a 50-foot stretch of road surface, Glover's milling crew milled three-quarters of inch off the travel lanes. The crew worked at night, milling approximately three miles and 385 yards of material, which was used to build up the shoulder base of the road. The goal was to stay two to three days ahead of the paving crew.

According to Lucky Harris, milling foreman, equipping the milling machine with leveling automation proved to be the best solution for achieving the smoothness specifications required.

"Since this project did not call for a leveling course, we used our milling operation as the leveling course," Harris says.

Approximately 50 percent of the entire project required full-depth milling due to severe structural deviations in the asphalt. Those sections were done first and replaced with six inches of intermediate HMA course, and then milled with the existing road to achieve a consistent surface. At the end of each overnight shift, crews had to sweep and stripe the milled surface before opening the travel lane back up to morning commuters.

One of the more challenging aspects of the milling operation was to establish a crown in the center of one of the travel lanes in order to accommodate future expansion of the highway. In order to achieve a 1.5 percent slope on the crowned lane, the milling crew had to adjust the seven-foot-wide milling head for each pass down the 12-foot-wide travel lane.

Paving operation

Twenty-four hours after the milling crew completed a three-mile stretch of road, Donald Uchima's paving crew took over. Using a Cedarapids 461 rubber track paver equipped with a Carlson EZ screed and float trackers, Uchima's 10-man crew put down 1,700 to 1,800 tons of HMA a day.