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Miscellaneous Considerations in Using Iron Oxide Pigments
Addtime: 2017/10/13 Read:4102 Font size: Large Small
Colorimeters or as generally referred to as Spectrophotometers are used to read color values of pigments. Caution should be used when applying the readings of this instrument in matching and controlling color for use in concrete. When reading a drawdown, the instrument reacts to the color produced by the pigment in a dry coating. Because the pigment develops in the concrete quite differently, two pigments that produce a match in a drawdown test may produce different color results in concrete.
Autoclaving of concrete presents a real problem when using Iron Oxide for coloring. While the reds and yellows do withstand the high autoclaving temperatures ( 300 to 350 F), the standard black pigment will not. Temperatures above 280 F will cause the black to oxidate turning it to a reddish tone that is not easy to control. High temperature black iron oxide are available that can withstand temperatures to 600 F. However these pigments are more expensive and of lower color strength.
Quality of iron oxide pigments vary from one manufacturer to another. Equal amounts do not guarantee the same color strength or value.
The fineness of the cement does influence the final color obtained. The finer cement requires more pigment to achieve the same results as with larger particle cement. Therefore control of the cement particle size is critical in developing good repeatability of color.
Water level in a concrete mix also affects the color development. Higher water level produces lighter grey concrete which results in a lighter final color.
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