Better Roads Staff
While concrete diamond grinding has been limited to smoothing rough concrete surfaces, the Next Generation Concrete Surface offers a new application for enhancement of PCC pavement smoothness, friction and, especially, noise created at the tire-pavement interface. That’s important, because noise is more and more considered an emission into the environment that must be controlled.
The NGCS is a diamond saw-cut surface, designed to provide a consistent profile absent of positive or upward texture, resulting in a uniform land profile design with a predominantly negative texture. NGCS is a hybrid texture that resembles a combination of diamond grinding and longitudinal grooving.
The texture is most easily constructed in a two-pass operation using diamond-tipped saw blades mounted on conventional diamond grinding and grooving equipment. Testing has shown that these textures can be used for both new construction and rehabilitation of existing surfaces.
The construction method has two separate operations, reports the Washington State DOT in its April 2011 report, Evaluation of Long-Term Pavement Performance and Noise Characteristics of the Next Generation Concrete Surface. The first operation creates a flush ground surface and eliminates the joint or crack faults while providing lateral drainage by maintaining a constant cross slope between grinding extremities in each lane.
The second operation provides the longitudinal grooves, Washington DOT reports. The longitudinal grooves are 0.125 inches wide and 0.125 to 0.375 inches deep. The longitudinal grooves are spaced approximately 0.5 inches center to center. The grooves are constructed parallel to the centerline.
Another variation of diamond grooving and grinding is “patch-and-grind.” Cook County, Ill., in the heart of the Chicago metro area, reports great success serving its road users by using the patch-and-grind method of concrete pavement restoration.
Patch-and-grind involves full- or partial-depth concrete pavement patching and joint repair, followed by diamond grinding of the entire pavement. The patching addresses structural issues such as cracked panels and spalled joints, while the diamond grinding addresses the functional deficiencies.
Patching without diamond grinding can result in poor rideability and is not an attractive alternative when considering the most effective use of the taxpayer’s money, IGGA reports. But the patch-and-grind repair method has proven to be a lower-cost construction alternative when compared to a full reconstruction, the association says. Motorists also realize the benefit of the shorter construction duration.
The Cook County Highway Department has used diamond grinding on a growing number of projects and the technique has migrated into adjoining Lake County, Ill. Full reconstruction of these pavements would have cost the taxpayers three times more than the patch-and-grind technique, IGGA says. A full reconstruction costs approximately $45 to $50 per square yard, while a patch and grind costs approximately $15 a square yard.
“When a typical full reconstruction of a lane-mile costs $1 million, the use of patching and grinding makes sense because it can be done at a fraction of the cost, provides long-lasting repairs and creates far less inconvenience to the motoring public,” says John Beissel, P.E., assistant superintendent, Cook County Highway Department.
Micromilling Fixes Cross Slopes
Micromilling with cold mills isn’t limited to preparing asphalt pavements for thin asphalt overlays. South Carolina is taking a leadership position on micromilling to correct cross slopes, and it shows in the increase of fine milling jobs undertaken by one contractor, Pavement Products and Services (PPS), Piedmont, S.C.
“South Carolina has a lot of ‘flat’ roads,” says Douglas E. Limbaugh, the company’s project manager. “The cross slopes are out of balance. So, we will surface-plane or micromill an inch or two off the road, to get the aged asphalt off, and once that’s done, variable surface-plane or cross-slope correct the main lines or roadways.”
By doing the planing in two stages, the company eliminates the drop-offs that would result in doing the work in one pass. “Motorists don’t have to drive with more than a 1-inch drop, and in the meantime they get a better surface to drive on,” Limbaugh says.
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