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The ability of a wide variety of clear coatings to protect the surface of exposed-aggregate and smooth white concrete against soiling by airborne industrial contaminants was investigated. Coated specimens of both types of concrete were subjected to a laboratory accelerated weathering test approximating the effects of these contaminants and then rated for color change. Based on these ratings and analysis of the coatings by infrared spectroscopy, it appears that low-viscosity acrylic resins based on methyl methacrylate generally offer the best protection for exposed-aggregate surfaces. The smooth concretes were more difficult to protect, and the use of higher viscosity materials, of higher solids content, is indicated. Many of the coatings used discolored permanently to various shades of grey, yellow, or brown. A limited number of coated exposed-aggregate specimens were observed in a highly industrial area for one year. The results of this exposure tended to verify the results of the laboratory tests. This report is also found on DVD021.
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