CONTRACTOR'S CHOICE GOLD: A micro scope

July 15, 2011

A major South Carolina asphalt milling subcontractor is using fine-tooth milling or “micromilling” to give South Carolina taxpayers smoother roads. Micromilling with a full-lane drum provides paving contractors a more even substrate on which to place asphalt lifts, essential for winning smoothness bonuses. For bonus-winning thin-lift hot-mix asphalt (HMA) layers micromilling is a must.

Last year, South Carolina was taking a leadership position on micromilling and it shows in the increase of fine milling jobs undertaken by the contractor, Pavement Products & Services Inc., Piedmont, S.C. One reason for the increase is that the state was correcting cross slopes. Also, by doing the planing in two stages, PP&S eliminated the drop-offs that would result from doing the work in one pass.

To do this work, PP&S was utilizing its Wirtgen cold mills both day and night.

One of the W 2200-12s was only three weeks old when it was put to work on I-185 in Greenville. In addition, work on I-185 west of Greenville—three lanes both north and south—was part of a total 1.4 million sq yd of 1-in. micromilling and 295,000 sq yd of variable surface planing for cross-slope correction. There, PP&S was using two full-lane W 2200s with a 12.5-ft drum and a half-lane micromill.

For super-smooth thin-lift HMA surfacings, cold-milling of the existing, worn surface with a fine-tooth drum is a must, said Jeff Wiley, senior vice president, Wirtgen America Inc.

“With a conventional drum, and relative to ground speed, your ‘peaks-and-valleys’ patterns will be relatively high and deep, and if you are not placing a lift that’s thicker than 1 to 11?4 in., the rough surface can reflect through to the paved surface,” Wiley said. “But with 5?16-in. bit spacing (or less), the definition of a fine-toothed drum, an owner or contractor can minimize the potential reflection of the peaks and valleys through the thin lift surface.”

PP&S hit the ground running, so to speak, with a brand new W 2200-12 in March 2010. “It’s working absolutely great,” said Douglas Limbaugh, operations, PP&S. “It’s humming along. The Level Pro system took a proven product—MOBA—and took it to another level. It’s improved the ease of use. I won’t say a caveman could do it but it makes a seamless transition from grade-to-slope, and slope-to-grade.”

In 2011, the W 2200-class cold mills were being supplanted by the new W 250 cold mill from Wirtgen America Inc., introduced at ConExpo-Con/Agg 2011.

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