Better Roads Staff
Diamond Grinding vs. Micromilling
By Tom Kuennen, Contributing Editor
Diamond grinding of Portland cement concrete pavements and micromilling of bituminous asphalt pavements are superficially similar in concept, but that’s just about the only thing they have in common.
Diamond grinding of aging Portland cement concrete (PCC) pavements renews the pavement’s skid-resistance, and provides a smoother-riding pavement. And the resulting smoother profile reduces dynamic loading on the pavement, thus extending its service life.
On the other hand, micromilling, or fine-tooth milling – using conventional cold mills with fine-tooth drums and hardened teeth – can remove imperfections from an asphalt surface and prepare it for a super-smooth thin asphalt overlay in a manner superior to conventional cold milling. In some cases, it can even be used instead of grooving or grinding pavements.
Following several years of research, promotion has begun for a new permutation of the diamond grinding process, the Next Generation Concrete Surface (NGCS). As promoted by the International Grooving and Grinding Association (IGGA), the NGCS is said to suppress noise from concrete pavements while enhancing friction and smoothness. The NGCS is being promoted following three years of research at the Minnesota Road Research Project (MnROAD), the world’s largest and most comprehensive outdoor pavement laboratory.
Early in 2011, new NGCS test sections were constructed at the Virginia Tech Transportation Institute’s Smart Road test facility near Blacksburg, Va. In January, three test strips situated on two test areas were constructed, including a conventionally-diamond-ground section, and an area that was conventional followed by longitudinal grooving of each half of the lane using two different groove spacings, of 0.5 and 0.75 inches respectively.
Each of the two test areas were ground one-lane wide and 528 feet long, and will allow the institute to study the impact of grinding and grooving on profiler measurements and on friction test results. In addition, the sections allow the future evaluation of splash and spray, as the Virginia Tech facility has this capability as well.
Diamond Grinding PCC Pavements
Diamond grinding is a concrete pavement preservation technique that corrects a variety of surface imperfections on concrete pavements, and should be used in conjunction with other pavement preservation techniques, reports IGGA.
It involves the removal of a thin layer of the cured concrete surface using a dedicated, self-propelled machine with closely-spaced diamond-coated circular saw blades. Diamond grinding restores rideability by removing surface irregularities. The immediate effect of diamond grinding is a significant improvement in the smoothness of a pavement, and a significant increase in surface macrotexture with improvement in skid resistance, noise reduction and safety.
The value of diamond grinding is borne out by a California Department of Transportation (Caltrans) study, conducted to quantify the expected longevity of a diamond-ground PCC pavement, and its overall effectiveness under various weather conditions and construction practices. In the study, Caltrans reported that diamond grinding “is a viable and cost-effective rehabilitation measure when properly applied. Diamond grinding not only extends the service life of a concrete pavement, but it also reduces tire-pavement interface noise and improves texture and skid resistance. Because the pavement is much smoother after grinding, highway user costs are also reduced through improved fuel efficiency and lower vehicle maintenance costs.”
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.
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