Road Science: Secrets to Successful Milling
Cold milling or planing is routinely used for “mill and fill” projects, where milling is followed sooner or later by a lift or lifts of hot mix asphalt which provide a new driving surface. But milling is much more than that.
Cold milling or planing can remove aged or damaged bridge decks, even those composed of tough, latex modified concrete; remove wheel ruts and improve friction coefficients; excavate damaged shoulders quickly and with minimal risk to workers or motorists; refine butt joints; restore road profiles; reveal curbs to improve storm water drainage; remove asphalt pavements full-depth; trim road bases prior to asphalt or concrete placement; and pulverize asphalt pavements.
“In recent years, the machines themselves have become a lot more productive with better technology, but the biggest thing that has happened is that they have become more reliable,” says Eric Baker, marketing manager for Roadtec, Inc. “With the first machines in the mid-70s you would work on them almost much as they would work for you. They were almost self-destructive. But with improved horsepower in the engines, improved component life, and better cutter technology, they’ve really evolved into a very reliable unit.”
The growth of asphalt milling in the context of both “green” construction and the burgeoning pavement preservation movement has resulted in a near-explosion of machines available to United States owners. The result has been an influx of new models.
For example, earlier this year at World of Asphalt, Volvo Construction Equipment introduced its MT2000 and MW500 milling machines. The MT2000 is a four-track, front-load, half-lane milling machine powered by a 610-horsepower Tier 3 Cummins engine. The MW500 is a four-wheel, rear-loading, utility-class milling machine that offers a standard cutting width of just less than 20 inches.
In 2006, BOMAG plunged into the North American market with its BM 2000 series, and the BM1000/30 and BM1300/30 models. They join offerings from long-standing manufacturers like Wirtgen America, Inc., Roadtec Inc., Terex Roadbuilding (formerly CMI Corp.), and Caterpillar Paving Products.
Planning for productivity
Planning a job each day is a key component of higher productivity, and that will mean planning the efficient use of trucks.
“For operators, the biggest thing they can do to enhance productivity is to think through the project the way a paver operator does,” Baker tells
“Operators need to be smart when it comes to managing trucks,” says Jeff Wiley, senior vice president, Wirtgen America, Inc. “Today’s machines have high productivity, and if you don’t have the right number of trucks for that that machine to feed and keep it running steady, you will be inefficient. The milling operation should actually mill and load trucks at least 40 to 45 minutes out of the hour. If you are not doing that, you are not efficient. Therefore the operator needs to balance the trucks, pace himself a bit, and keep the machine running steady. That’s in place of running the machine wide open, then waiting 15 to 30 minutes for trucks to return.”
How truck use can boost productivity was illustrated by a project this spring at Las Vegas’ McCarran International Airport. There, Las Vegas Paving faced a $500,000-per-day disincentive for not completing the project on time when it began a six-month, $75 million milling and paving project on the airport’s busiest runway, 25L/7R, on Nov. 1, 2008.
In part the project involved removing asphalt from the entire 10,525-foot-length of the runway and an 11,000-foot-long taxiway, using two Terex PR800 7-12s and a three-track Terex PR950. Las Vegas Paving’s crews worked 24 hours per day, 7 days a week for the first month, and the mills ran 20 to 22 hours per day, stopping only for fuel and daily maintenance between the two twelve-hour crew shifts.
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