Coloured concrete is the result of aesthetic treatments, based on the usage of pigments on the concrete’s bearing layer. In addition to an effective wear-resistant coating, a desirable finish is achieved.
Coloured concrete shouldn’t be confused with a floor covering such as an epoxy floor.
Colouring concrete techniques
Generally, there are 2 ways to achieve concrete colouring.
The first technique consists of stamping the concrete, where prior to placing and pressing of the texturing moulds, layers of colourant are added to the fresh concrete.
These colourants are pigments in a powder form, although they can also be liquid. This will determine the colouring process and finishing requirements.
Another technique applied in construction is based on incorporating the colourant directly into the traditional concrete mix. This mixture is usually made up of stone aggregates, sand, cement and water (and frequently additives).
Unlike stamped concrete, this technique requires the colourant to be a powdered pigment.
These pigments are inorganic materials of mineral origin. The most commonly used are iron and chromium oxides.
Alternatively, in the second technique, colour cements can be used instead of pigments and conventional grey cements.
Most commonly used pigments in printed concrete
Colours in printed concrete are obtained by adding pigments. These can be classified as either natural or synthetic.
Natural pigments come from mineral deposits. They are composed of metallic oxides and hydroxides, with iron being the most common metal used to apply pigmentation.
Synthetic pigments are, like natural pigments, metallic oxides. However, these originate through industrial processes. In these processes, the raw material (minerals) is refined to modify its physio-chemical properties.
Each metallic oxide is linked to a specific colour, depending on its physio-chemical properties. By doing so, the most frequently used for the stamping and colouring of concrete are the following:
- Chromium oxide: this pigment is responsible for green tones in the concrete.
- Titanium dioxide: it grants traditional concrete with the colour white.
- Cobalt oxide: a pigment that creates blue concrete, in intense shades like navy blue, or light shades like light blue.
- Iron oxide: ferric oxides are used to obtain a wide range of colours and shades. The usual ones are: red, orange, yellow, black and different shades of brown.
In addition to pigmentation, coloured concrete can be obtained by using coloured cement. This type of cement is the result of mixing traditional Portland cement with colourant during the grinding process.
The amount of colourant material corresponds to 5-10% of the weight of Portland cement, the last being the maximum amount.
Consequently, the colouring material only represents between 1% and 2% of the total mass of a coloured concrete.
Of all coloured cements, white cement is the best known and used. It’s produced by using pure and poor raw iron materials, which are heated in rotary kilns.
During this process the peculiarity arises that the particles of coloured cement tend to be smaller than those of traditional cement.
White cement is used to produce any other coloured cement, to develop the lightest and most opaque shades. However, darker shades can be obtained by using traditional Portland cement.