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Concrete Pavement Research & Technology INCORPORATING COLORED CROSSWALKS IN CONCRETE PAVEMENTS The use of decorative concrete has increased dramatically in the last few years, especially for urban streetscape programs intended to revitalize downtown areas in small- and medium-sized towns and cities. A common location for decorative (stamped and/or colored) concrete in roadway pavements is at crosswalks. The colored concrete can help serve as a pavement marking if the standard white stripes identifying the crosswalk wear off. The colored crosswalk still alerts pedestrians and motorists of the crossing, making for safer pedestrian/vehicle intersections. Decorative Concrete Basics Many colors and textures are available to enhance the appearance of a concrete surface, often providing a cost-effective simulation of natural stone, brick, or other materials. Integrally colored concrete is made by adding mineral oxide pigments to concretes made with portland cement. The concrete aggregates, particularly fine aggregate, must be carefully selected to enhance the color effect. The amount of coloring material added should not exceed 10% by weight of the cement, because larger amounts of pigment may excessively reduce the concrete strength. Strong color can usually be produced with less than 10% addition of pigment. Different color intensities are achieved by varying the amount of coloring material or by mixing two or more pigments. Red, tan, dark gray, and other hues are produced very satisfactorily using normal cement. However, avoid admixtures that contain calcium chloride since it can cause discoloration. Variations in the components of the concrete mix make color formulas approximate. Experiment with trial mixes for best results. After a basic color is selected, the exact shade may be determined by preparing a number of small panels and varying the ratio of pigment to cement. Once the desired shade is selected, be sure to use the same materials and proportions in all of the actual work. To properly evaluate panels, store them for about five days under conditions similar to the jobsite. Panels will be darker when damp than when dry. Coloring Materials Finely ground iron oxides, either naturally or synthetic, are the most widely used pigments for coloring concrete. Chromium oxide and cobalt oxide usually cost significantly more than iron oxides. Do not use untreated carbon black and lampblack because they are unstable, fade, and reduce air content in the concrete. Pigments should meet quality standards of ASTM C 979. • For BROWNS, use brown iron oxide • For TANS, use yellow iron oxide • For REDS, use red iron oxide • For GREENS, use chromium oxide • For BLUES, use cobalt oxide • For GRAY or SLATE, use black iron oxide Number 5.03 March 2004 P\Gp,N Coy American Concrete Pavement Association c9 5420 Old Orchard Rd. c Fm Suite A100 Skokie, IL 60077 p Phone: 847-966-2272 Fax: 847-966-9970 ��F�7 Ass o�\P www.pavement.com