Hydraulic cement is a powdered mineral mixture that hardens when combined with water. In 1824, Joseph Aspdin invented portland cement, which is a main ingredient in concrete. The eight types of portland cement range from Types I and IA, which are suitable for most structural uses, to Type V, which is suitable for structures exposed to sulfate from soil and groundwater. Other types of cement include blended cements, expansion cements and white cement. Gray cement and white cement have the same structural capacities but different processing requirements.
Raw materials that make up portland cement include limestone, seashells, clay and iron ore. Manufacturers obtain these raw materials from quarries or mines. Gray cement obtains its color from raw materials that contain iron, manganese, chromium and magnesium oxides. To produce white cement, manufacturers must use limestone or other raw materials that contain very low levels of these oxides. White concrete cement must contain aggregates, such as marble, that do not add color.
White and gray cements go through grinding and heating processes. In a kiln at 2600 degrees Fahrenheit, combined raw materials for gray cement form hard, dark-gray pellets known as "clinkers." Producers add gypsum to the cooled clinker and grind the ingredients into a fine, powdered gray cement. White cement powder has greater reflective surface because it is usually finer than gray cement powder. The University of California at Berkeley recommends using ceramic mill liners and grinding equipment for white cement production, because metallic equipment can contain color-altering iron and chromium.
Gray cement is a durable material for bridges, buildings and other structures. According to the Concrete Network, gray cement costs about half as much to produce as white cement and is more widely available than white cement. White cement, which has the same structural capabilities as gray cement, adds decorative drama to archways, hotels and cathedrals and never requires repainting. White cement's reflective properties add visibility to highway medians and energy efficiency to building interiors. During cement production, selected color pigments can add permanent, decorative colors to white cement.
According to the Concrete Network, white cement concrete projects require special supply and preparation considerations. To maintain uniformity of appearance, builders for a massive construction project must obtain large quantities of white cement from a single major producer. The Concrete Network states that builders should set aside truck mixers and aggregates exclusively for white cement concrete to prevent color-altering dust or fiber contamination. Leakproof and stainproof fiberglass or plastic forms prevent spots and stains in white cement concrete.