Coloured Concrete

Property owners, designers, and architects are always on the watch out for techniques to improve the look of their properties at a practical cost. Coloured concrete is an answer to their needs.

Coloured concrete is used to anything and everything, from decorate pavement areas as well as structure interior floors. Coloured concrete is attained by adding oxides (dosed either by kg/m3 or as percentage of cement content of the mix) to the concrete at the time of mixing.

Since its introduction in 1950s, coloured concrete has been very popular and its popularity has been increasing over the years. Not only colours, today concrete can also have geometric patters or artistic images to decorate it. With numerous choices to choose from, it can actually become difficult to select the coloured concrete for your project. This article puts together information about how colour concrete is formed.

Colour is added to the concrete to form colour concrete. This can be done by two methods which are by using ready coloured cement or by amalgamating a colouring agent into the concrete during the initial process of mixing. The colour is determined by the pigments selected, that is, natural or synthetic.

Colour concrete that is prepared by natural pigments are made from mined ores such as manganese or carbon which is black in colour, chromium which is green, brown, yellow or red in colour or cobalt spinals which is blue in colour. However colour concrete that is made by synthetic pigments are made from by – products of steel, iron salts or scrap steel dissolved in acid and precipitated. These pigments come in black, yellow and red colours. For permanent colour concrete, the selection of desired colours has to be done very carefully. The exposed colour aggregates give a permanent colour to the concrete and also minimises the effect of the ultra – violet illumination and other stains such as efflorescence.
Efflorescence (white deposits observed on the surface of the concrete) is a common cause that leads to fading of colour in a colour concrete. Lime weeping and lime bloom are the commonly experimental forms of efflorescence. The dissimilarity between lime weeping and lime bloom is the physical appearance of lime weeping that forms blemishes or hazy lazy layers which become evident when the concrete begins to dry out. The effect of efflorescence on the appearance of a concrete structure has been a cause for apprehension for many since a while now. As the intensity of colours used rises, the consequence of efflorescence on coloured structures also becomes undesirable.
Coloured concrete can be produced in one of these methods:

• Integral colour: Integral colour is the colour that is introduced during the batching of the concrete on wearing screeds. The approach is to produce trial mixes which are assessed until the concrete colour is satisfactory for durability, strength and colour of the concrete. This method is used for earthy tones and less intense colours. It is also used when the concrete quality is enough for abrasion.

• Dry shake: Dry shake is the colour that is applied after the hardener is applied. The use of hardeners can boost the abrasion resistance of the surface and may provide slip resistance. This method is used for intense colours which include textured finishes to give slip resistance. It is also used for stamped or pattern imprinted slabs and in cases when enhanced abrasion is required.

• Penetrating reactive chemical stains method is used for creating a variegated patina which is purely decorative. This method is an alternative to painting.

• Painting and coatings method provides a wide range of colours. It is also used when the requirement is purely decorative.