Stretching a road maintenance budget with fine milling
Doing more with less and aggressively seeking new ways to stretch budget dollars are how many businesses respond to a tough economic climate. Federal and state highway and transportation departments are no exceptions. Fortunately, academic research and equipment technology communities together have some promising results to share.
The National Center for Asphalt Technology (NCAT) on the campus of Auburn University (Auburn, Ala.) recently completed a study for the Alabama Department of Transportation (ALDOT) showing that pavement design standards used by many state transportation agencies for decades can be updated to reflect new asphalt material mixes and roadbuilding methods.
Specifically, after thoroughly testing various asphalt layer coefficients on its test track, NCAT’s results determined asphalt pavements can be safely built about 18 percent thinner. This means more highway departments can build and resurf
ace more roads without suffering any degradation in road performance.
Such new standards are also leading to new road-repair efforts to help stretch maintenance dollars. Traditional mill-and-fill efforts involve using road-milling machines with standard-spacing road-milling drums (bits spaced 5/8 inches or roughly 16 mm apart) to remove pavement for rebuilding. A new alternative, fine milling, involves swapping out a
standard road-milling drum for a fine-milling drum with much tighter tooth spacing, 0.3 inches (8 mm) or less. This permits removing only a minimal depth of road surface depending on conditions and replacing it with thin hot-mix asphalt (HMA) overlays. Using thin HMA overlays can stretch maintenance budgets, but also requires fine-milled surfaces so the surface’s peaks and valleys don’t reflect through the new thin overlay.
Fine milling can address other road-repair conditions.
For example, excessive road-mix binder can accumulate on a road’s surface, depending on traffic loads and environmental conditions. This causes a polished surface and increases the chances of accidents due to decreased skid resistance. Where removing the entire road’s surface course and replacing it would have been the conventional solution, fine milling can remove only a top portion of the surface course needing replacement.
Wheel ruts can be efficiently removed by scarifying to a level below the overroll created by traffic and uneven road grades can be quickly fixed. Savings accrue from a number of related areas:
- Less damaged road material needing to be removed
- Less repair material needed
- Milling crews can operate independently from paving crews
- With less material removed and less repair material required, the number of haul trucks is significantly reduced
- Project and contractor costs are more efficiently controlled, expanding the scope and number of repair projects where necessary
How It Works
As previously mentioned, fine milling involves swapping out a milling machine’s standard road-milling drum (bits spaced roughly 16 mm apart) with a fine-milling drum exhibiting more closely spaced bits, 0.3 inches (8 mm) apart or less. Drums also include conical tools, sleeves, and blocks in a range of available styles, including weld-on blocks and proprietary quick-change systems requiring no welding and, in certain applications, no bolts.
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