PRODUCTION OF COLORED CEMENT-CONCRETE PRODUCT

PURPOSE:To obtain a colored concrete product having a strong colored coating mainly containing a metal sulfate and stable in color tone in high efficiency by applying an aqueous solution of the metal sulfate on the surface of a concrete article and subjecting to steam aging. CONSTITUTION:An aqueous solution of a metal sulfate is impregnated into and/or applied on the surface of a cement-concrete article. The metal sulfate can be selected from copper sulfate, chromium sulfate, manganese sulfate, iron sulfate, etc. Subsequently, the treated cement-concrete article is subjected to steam aging to obtain a colored concrete product having a colored coating mainly containing the metal sulfate and/or its reaction product on the surface of the cement-concrete article. Further, the coloring is promoted and the colored coating is formed in an early stage by treating the surface of the cement- concrete article with an activating agent, e.g. an alkali aqueous solution (e.g. an aqueous solution of sodium hydroxide) or an aqueous solution of an oxidizing agent (e.g. an aqueous solution of hydrogen peroxide) before or after the impregnation and/or the coating of the metal sulfate aqueous solution.