Better Roads Staff
Diamond grinding provides a smooth surface that can reduce dynamic loading and increase pavement longevity, IGGA reports. Increased pavement life will be obtained by reducing the roughness, IGGA maintains, and can be demonstrated using the American Association of State Highway & Transportation Officials (AASHTO) 1993 Pavement Design Equation. In that equation, serviceability is analogous to smoothness, which means that increased serviceability (a smoother pavement) will result in more equivalent single-axle loads carried by the pavement, the association says.
Diamond-ground surfaces have been found to reduce accident rates, IGGA reports. The Wisconsin DOT, working with Marquette University, found that the overall accident rate for diamond-ground surfaces was only 60 percent of the rate for nonground surfaces. The diamond-ground pavements provided significantly-reduced accident rates up to six years after grinding.
While creating a smoother pavement, diamond grinding does not affect the fatigue life of a pavement and does not raise the pavement surface elevation. Grinding also does not affect the hydraulic capacities of curbs and gutters on municipal streets, unlike bituminous overlays that fill curb and gutter, and reduce their drainage capabilities, IGGA says. Diamond grinding can be applied only where improvement is needed, and can be performed during off-peak hours.
Micromilling Asphalt Pavements
Unlike diamond grinding, micromilling pavements do not require a dedicated machine, as they can be applied by a conventional asphalt cold mill fitted with a fine-tooth drum.
This is particularly important when placing so-called thin HMA overlays, microsurfacing or other spray surface treatments. There, micromilling is preferred to a conventional drum because the latter provides a “peaks-and-valleys” pattern that will be relatively high and deep. If an agency is not placing a lift that’s thicker than 1 to 1-1/4 inches, the rough surface can reflect through to the paved surface. But with 5/16-inch 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.
Georgia DOT’s micromill spec – Section 432: Mill Asphaltic Concrete Pavement (Micro-Mill) – describes micromilling of existing asphalt concrete pavement to remove wheel ruts and other surface irregularities, and restore proper grade and/or transverse slope of pavement as indicated in the plans or as instructed by the engineer.
“The planed surface shall provide a texture suitable for use as a temporary riding surface or an immediate overlay with OGFC [open-graded friction course] or PEM [porous European mix] with no further treatment or overlays,” Georgia DOT says in its spec, and limits use of the micromilled pavement as a temporary riding surface to a maximum of seven days.
• equipped with a cutting mandrel [drum] with carbide-tipped cutting teeth designed for micromilling bituminous pavement to close tolerances;
• equipped with grade and slope controls operating from a stringline or ski and based on mechanical or sonic operation;
• capable of removing pavement to an accuracy of 1/16 inch (1.6 mm);
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