Thursday, December 28, 2000 - 09:17

Diamond-Grade Pavements

State departments of transportation are beginning to realize the benefits of diamond grinding as a viable alternative to using asphalt overlays to restore distressed concrete pavements.
The process is an important element of concrete pavement restoration (CPR) and is used to restore or improve pavement rideability and enhance the inherent friction characteristics of concrete pavements.
Diamond grinding was first used in 1965 to eliminate excessive faulting on a 19-year-old section of I-10 in southern California. It was used as the final step in the CPR program, which also involved full- and partial-depth repairs and installation of edge drains, to provide a very smooth riding surface.
Despite its history, however, very little documentation exists on the performance of diamond-ground pavements. To provide the necessary documentation, the Portland Cement Association, together with the American Concrete Pavement Association (ACPA) and International Grooving & Grinding Association—sponsored a study to evaluate the performance of diamond-ground pavements.

Research overview
Performance data were obtained through field surveys and from existing databases, the main source of which was a database of 121 diamond-ground pavement sections created for a 1989 Federal Highway Administration-sponsored study of concrete pavement rehabilitation.
The field survey for the current study focused on revisiting all surviving sites from the 1989 FHWA study. At the time of the field survey in fall 1997, 38 of the 76 sites were surviving, all of which were revisited. The field survey sites also included additional sections, totaling 181 in all.
Another important source of existing data for diamond-ground pavements is the Long-Term Pavement Performance (LTPP) Program database. The LTPP SPS-6 sections, concrete pavement rehabilitation, provide the opportunities for direct, side-by-side comparison of the performance of diamond-ground pavement sections and other rehabilitation alternatives, including asphalt- concrete (AC) overlays.
The tests were used to analyze service life, faulting performance, longevity of diamond-ground texture, and the effects of diamond grinding on slab cracking.

Study results
The study showed that CPR with diamond grinding is an effective means of extending the service life of concrete pavements and imparting a smooth pavement surface with the desirable surface texture. The study also emphasized that the process can be used to address a number of issues, including faulting at joints or cracks; roughness; polished concrete surfaces exhibiting inadequate macrotexture; wheelpath rutting; unacceptable noise levels; permanent upward slab warping; and inadequate transverse slope.
Diamond grinding can be performed during off-peak hours with short lane-closures. It does not raise the pavement surface elevation—and in fact, it can be feathered into adjacent pavement structures—so it can be performed selectively on sections where repair is required rather than across the entire width of the roadway.
The study also showed that the level of smoothness that can be achieved through diamond grinding is equal to or better than that of a new pavement or overlay. According to the study, the removal of hardened PCC with closely spaced diamond saw blades leaves a longitudinal groove-like texture, which increases “macrotexture.” This in turn improves friction and drainage of water at the tire/pavement interface, thereby reducing accidents.
In addition, the textured pavements also are quiet. A multi-state study on noise and textures, sponsored by the Wisconsin DOT and the FHWA concluded that longitudinally textured concrete pavements are among the quietest pavements for interior and exterior noise. The process also removes faults by leveling the pavement surface, thus eliminating the “thumping” and “slapping” sound created at joints.

Long-term effectiveness
The field evaluations showed that CPR with diamond grinding was effective in extending service life at numerous projects. The average age at failure of the sections evaluated was 30.4 years, with many sections surviving 40 or more years.
After evaluating service life, faulting and surface texture, the study showed that a diamond-ground surface may be expected to extend pavement life between 8-20 million ESALs, depending on the climate. Cracking analysis showed that a pavement slab could be reground up to three or four times without compromising fatigue life. No evidence of any deleterious effects of diamond grinding was observed at any of the field sites.

Projects illustrate merits
The study also includes a number of examples that underscore the longevity of diamond-ground concrete pavements. The following are highlights of two of these examples.
I-10, San Bernardino County, Calif., is a diamond-ground, jointed, plain concrete pavement (JPCP) section near Fontana. This is the historic 1965 project where continuous diamond grinding was first used on a concrete pavement. The pavement structure consists of a 8-in. slab on a 3-in. asphalt-treated base with a 15-ft constant joint spacing. This pavement was constructed in 1946. In 1965, two lanes in each direction were added on the inside to widen the four-lane freeway to eight lanes. The original truck lane was diamond-ground.
By 1984, the two-way average daily traffic (ADT) on this pavement was 84,000, and the truck lane had carried more than 19 million ESALs since construction. Retrofitted edgedrains were installed and the pavement was diamond-ground for a second time in 1984. In 1997, 51 years after construction, this pavement was ground for the third time. The current ADT on this freeway is 158,000, which corresponds to more than 2.25 million ESALs per year on the truck lane. The truck lane has carried more than 24 million ESALs since rehabilitation in 1984 and more than 43 million ESALs since construction.
This 51-year-old pavement is an excellent showcase of the endurance and durability of concrete pavements and effectiveness of CPR with diamond grinding. Though the 1997 survey showed low-severity cracking, further extension of the service life is expected due to grinding. Even 14 years after the second grinding, this undoweled, 8-in. JCPC had only an average fault rate of 0.10 in.
Trunk Highway 10, Elk River, Minn., also are projects included in the 1989 FHWA study. This portion of TH10 is a 8-in nondoweled JPCP on a 3-in. aggregate base with 15-ft joint spacing. It was constructed in 1946 and rehabilitated in 1982. The rehabilitation consisted of diamond grinding and joint sealing in the east-bound truck lane and grinding, joint sealing and edge support installation in the west-bound truck lane.
This project had been subjected to relatively low levels of traffic. In 1997, the truck lanes had approximately 2.5 million ESALs since grinding and 5 million ESALs since construction. Some sections in the east-bound direction have been overlaid. The faulting in this truck lane in 1997 ranged from 0.02 to 0.13 in., with an average value of 0.07 in. The average faulting in 1986 was 0.04 in. The east-bound section had a high number of transverse and longitudinal cracks. Fifty-six percent of the slabs in this section had low severity longitudinal cracking and low- to medium-severity transverse cracking. The west-bound section had fewer transverse cracks and no longitudinal cracks, but the average faulting was the same as that in the east-bound section, 0.07 in.
This is an example of a low-volume rural highway that has lasted more than 50 years since construction and more than 15 years since rehabilitation.
The study—and the case studies—lend evidence to many of the long-standing beliefs about the benefits of using diamond grinding as part of CPR. The results are smoother, quieter, safer pavements that last.
For a complete copy of the research study results, please contact ACPA at 5420 Old Orchard Road, Suite A100, Skokie, IL 60077-1059, or call 847/966-2272; fax 847/966-9970.

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