Pigments are products that give color to products, while they are in a mixture in the solid phase (in the form of particles) and do not enter into chemical reactions with the components of the mixture.
For dyeing a concrete mix, you must use a pigment that meets the basic parameters:
• light resistance – resistance to UV exposure (burnout);
• alkali resistance – resistance to the chemical action of an alkaline environment, which creates cement (the final products of the reaction can be efflorescence on the product).
Pigments in the mixture dye only cement, enveloping the cement grains with their particles. Therefore, the concentration of pigment in the mixture is calculated in% by weight of cement. With a very high percentage of pigment in the mixture, the strength of concrete is significantly reduced.
By origin, pigments are divided into several major groups.
1. Iron oxide
a) natural iron oxide:
red lead – 5% by weight of cement to obtain a saturated color;
ocher – 5% by weight of cement (saturated color);
b) synthetic iron oxide:
red, dark red (cherry), yellow, light brown, brown, dark brown, black – 3% by weight of cement (rich color). Maximum – 5%.
Blue, green – 0.5% by weight of cement (saturated color). Maximum – 1%.
Phthalocyanine pigments are the most light-resistant, they have a very high dispersion, which leads to good staining ability with a small percentage.
3. Chromium oxide pigment
The chemical composition of chromium oxide is almost pure chromium oxide. The color is olive-green with different shades from yellowish to bluish, insoluble in water, ethyl alcohol, acetone, hardly soluble in all alkalis and acids. As the pigment has a high hiding power.
Green – 3% by weight of cement (saturated color). Maximum – 5%.
4. Soot pigment (carbon technical)
Black 3% by weight of cement (rich color).
5. Dioxide (oxide) of titanium
Titanium dioxide is used to produce pure white. When using titanium dioxide in a large percentage, there is no noticeable decrease in strength. Therefore, in order to obtain optimal white color, it is necessary to apply 2% pigment by weight of the whole mixture (sand + cement). Maximum – 4%.
Some pigments affect the water-cement ratio of the mixture. White pigment (titanium dioxide) dilutes the mixture. Carbon black (technical carbon) makes the mixture more rigid (dries). This must be taken into account when producing the mixture.
Do not allow dry pigment on the form. This leads to damage to the appearance of the entire product and, consequently, to financial losses.