Application of Dyes and Pigments
Since many years, people have developed many interesting effects by mixing cement and pigments in different ways and in different proportions. Concrete is derived from cement. For about last one century, pigments have been using with concrete to give them different colors. When pigments are mixed with concrete, then actually, these pigments tint the color of the paste portion of the concrete.
To ensure a long lasting cement color shade, the pigment that is being used in the cement, must have a good quality. These pigments (color) are made from both natural and synthetic Iron oxide, cobalt, titanium dioxide and chromium oxide. From iron oxide pigments, red, black and yellow color can be obtained. From cobalt pigments, blue color can be obtained. White color and green color can be obtained from titanium dioxide and chromium oxide respectively. Other colors like buffs, brown, tans, coppers, oranges, chocolates and many other colors can be obtained from the blends of the red, black and yellow colored iron oxide pigments. These colored pigments are: water- wetable, lightfast, alkali resistant and will not negatively effect the firmness and strength of the cement. But, one thing should we remember about the concentration of these pigments in the cement. This concentration should be within the range of 10% of the weight of the cementitious ingredients.
Iron Oxide Pigments
One of the most commonly used pigments with concrete is Iron Oxide Pigments. Iron Oxide pigments are combined with concrete to protect the concrete form fading or prevent the leaching out of concrete. The primary colors of Iron Oxide Pigments are available in red, yellow and black. With the red colored Iron Oxide pigments, shades of blue or orange can be found. To create multitude of colors, these pigments having of different colors are combined together according to a certain ratio. Still today, the use of Iron Oxide pigments is maximum. The few reasons of this popularity of this pigments in the cement industry are:
Chromium Oxide generates the green effect in the cement. But, it is expensive one. So, it is used in some special cases.
Cobalt generates the blue effect in the cement. But, it is expensive one. So, it is used in some special cases.
Titanium dioxide produces the white color effect in the cement and other related materials.
In general, pigments don't react with cement, because pigments are inert in nature. So, pigments are not be counted as cementitious material contents. Then, the question arises, that how pigments are applied with cement. Actually, whenever pigments are mixed with cement then, these pigments form color of cement grains. This is possible, because pigments bond with the cement via the hydration process.
The different pigment that are used in cement industry, are available in different forms. These different forms are: Powdered form, Granular form and Liquid form. Although, pigments work well in all three different forms, but, these require different handling process and composition should be different. However, the oldest form of pigments is the powder form.