This Technical Advisory was canceled on June 17, 2005
U.S. Department of Transportation
Federal Highway Administration
TEXTURING AND SKID RESISTANCE
OF CONCRETE PAVEMENTS AND BRIDGE DECKS
September 18, 1979
PURPOSE. To issue guidance for providing an adequate level of wet pavement skid resistance on Portland cement concrete (PCC) pavement surfaces and plain or latex modified concrete bridge deck surfaces.
CANCELLATION. This issuance supersedes FHWA Notice N5080.59 dated September 10, 1976, "Texturing of Concrete Pavements and Bridge Decks."
If a pavement or bridge deck surface is to provide adequate skid resistance for high speed traffic, two important, and to some extent independent, requirements must be satisfied. First, the pavement surface must provide for adequate adhesion between the tire and the pavement under wet weather conditions. Second, the pavement surface must provide sufficient surface texture and drainage potential to prevent the buildup of water pressure at the tire-pavement interface. On PCC riding surfaces, this drainage potential can be provided initially by the texturing of the concrete surface. The adhesion component of skid resistance is dependent on the wear and polish resistance characteristics of the aggregates.
A concrete finishing procedure that will provide an adequate and durable skid resistant surface texture is needed on all pavement and bridge deck surfaces.
While a skid resistant surface texture is needed on all pavement surfaces, the need may be especially critical on bridge decks because of the limited recovery area available to out-of-control vehicles.
A burlap drag finish should not be used as the sole means of providing surface texture on projects with design speeds of 40 miles per hour (65 km per hour) or greater.
A broom or artificial grass drag finish, while often producing good initial surface texture, may not be durable unless a deep texture is produced by heavy bristles and high pressures. When a broom, artificial grass drag, or similar finish is specified for use on projects with design speeds of 40 miles per hour (65 km per hour) or greater, specifications that will insure a deep, durable texture must be used. Also, it should be conclusively demonstrated that safe, durable surfaces can be consistently produced by finishes before they are utilized extensively on high speed highways.
Metal tines, when preceded by a burlap or other type of drag finish, are recommended as being the most practical and dependable method of providing positive texture in PCC surfaces. The use of other procedures and equipment that will provide a similar grooved pavement surface is also encouraged. An Attachment to this advisory provides a summary of some of the more important research findings and recommendations relative to the texturing of PCC pavement surfaces.
The use of a deep surface texture on bridge decks may warrant increased concrete cover over the top layer of reinforcement steel beyond the 2.5 inches (63 mm) required for minimum design cover and construction tolerance. The use of heavy transverse textures may also increase the concentration of deicing salts along the curb line unless proper provisions are made to drain these areas. The last 12 inches (300 mm) of deck next to the curb, should be left untextured to facilitate drainage.
Special techniques may be required in order to produce a durable grooved finish on latex modified and other lowwater-cement ratio bridge deck surfaces. The use of flexible tines on such surfaces frequently fails to produce a groove depth sufficient for reasonable durability. In at least one State, satisfactory grooves have been produced in these dense surfaces through the use of a roller consisting of sharpened flat washers welded at intervals onto the outside of a weighted section of pipe. Other techniques may also prove to be successful. As is the case with pavement surfaces, it is normally desirable that the plastic grooving application be preceded by a burlap or other drag finish or a light broom finish.
Regardless of the finishing or texturing method used, adequate durable skid resistance characteristics cannot be attained unless the fine aggregate has suitable wear and polish resistance characteristics. Research conducted by the Portland Cement Association indicates that the siliceous particle content of the fine aggregate should not be less than 25 percent. If past experience indicates that the coarse aggregates will be exposed by surface wear and have a significant effect on the skid resistance of the pavement, they, too, should have suitable polish resistance characteristics. Crushed material will normally provide higher skid resistance than uncrushed gravels.
Associate Administrator for
Engineering and Traffic Operations
TEXTURING OF PCC PAVEMENT SURFACES
Transverse grooving will assist in providing a pavement surface with good durable pavement skid resistance characteristics at high speeds, will reduce splash and spray and headlight glare from wet roadway surfaces, and will continue to facilitate surface drainage until the depth of the wheelpath ruts exceeds the depth of the grooves. Longitudinal grooving assists vehicle control at curves and sites involving lateral movements. Both types of grooving effectively reduce the hydroplaning potential. The longitudinal grooving of existing pavements, while not necessarily producing an improvement in skid number, has been found to be an effective means of reducing accidents at sites having high, wet weather accident rates.
Although longitudinal grooving may be preferable under some circumstances, and particularly when dealing with existing pavements, transverse grooving is considered to be superior to longitudinal grooving for general use on new construction because of the improved pavement drainage provided. Also, with the increased use of smaller, lighter cars and radial tires, complaints of vehicle handling problems on longitudinal grooved pavements seem to be on the increase.
From the standpoint of compatibility between tire tread designs and pavement texture, it is desirable that, to the extent practical, longitudinal grooving patterns be standardized. The use of 0.095-inch (2.4 mm) wide grooves spaced on 3/4-inch (19 mm) centers is recommended. There is insufficient information available on which to base recommendations regarding the optimum texture for a milled PCC pavement riding surface. Some extremely harsh milled surfaces may be unacceptable for use as a riding surface.
The use of tines 0.03 inches (0.8 mm) thick, 0.08 inches (2.0 mm) wide and 4 to 6 inches (100 to 150 mm) in length has resulted in good, durable surfaces when the grooves were constructed to the maximum depth practical. This maximum practical depth, which will vary depending on the concrete mix design and other factors, is normally in the 1/8-inch (3 mm) to 3/16-inch (5 mm) range. Average transverse groove spacings of approximately 1/2 to 3/4 inch (13-20 mm) arerecommended. Groove spacings of less than 1/2 inch (13 mm) may not have adequate durability. An increase in average groove spacing beyond 3/4 inch (20 mm) cannot be expected to increase durability by a significant amount and may lead to noise problems. Relatively uniform groove spacings of 1 inch and 1 1/2 inches (25 and 38 mm) have in some instances been considered unacceptable because of the concentration of tire-pavement noise into an objectionable frequency band. Experience with average groove spacings exceeding 1 1/2 inches (38 mm) is too limited to facilitate the drawing of any conclusions. The use of wider, deeper grooves can be expected to increase the absolute noise level by a significant amount. Randomization of the groove spacing, which may result to some extent from the flexibility of the tines, is considered desirable from the noise standpoint.
The optimum length and angle of the tines will be dependent on the mix design, the weather, the finishing operations, and the stiffness of the tines and may be expected to vary somewhat from project to project.
The timing of the plastic texturing operation is critical. If performed too early, the grooves may close back up. If performed too late, the groove depth will be reduced. The optimum time for performing the plastic grooving operation will be dependent on many variables which are subject to rapid fluctuations.
When a tine finish is utilized, care should be exercised to avoid overlaps in the texturing operations. The overlaps will result in weak areas which will wear faster than the normal texture. For the best initial surface texture, a tine finish should be preceded by a burlap or artificial grass drag finish.
Because of the increased surface area, deeply textured surfaces will require a heavier than normal application of curing compound.
A tire tread depth gauge may be used to measure groove depths both in hardened and plastic concrete. When measuring the depth of fresh grooves formed by the tining of plastic concrete, it must be recognized that an artificially high reading may be obtained that will not be representative of the actual groovedepths that will exist after a few months' exposure to traffic. To insure that the tined grooves will be durable and effective, it is essential that they be made as deep as practical during construction.