More About Concrete Oxides

 

pigments.jpgIntegrally coloured concrete or full depth coloured concrete involves colouring the entire wet or new concrete, all the way through the slab. This is usually achieved by the addition of synthetic mineral oxide pigments, more commonly known as oxides into wet premixed concrete during the batching and mixing processes.

CCS oxide pigments are a highly effective colourant used to colour 100% of the concrete.  The oxide pigments are an ultra fine powder and unlike a dye that colours by a staining action from a dissolved solution, pigments are insoluble in most liquids including water.

Once added, the ultra-fine mineral oxides disperse throughout the wet concrete mix and bind with the cement matrix in the same way as aggregates do.

As pigments are made from metallic oxides or materials in their most basic form, there is no mechanism for them to degrade or change colour over time. They are not affected by the sun's ultraviolet rays, are light fast (eliminates fading) and once bound into the concrete matrix they provide a permanent colouring solution.

They are also insoluble (prevents leaching out), chemically inert (do not interfere with the hydration of the cement), alkali resistant (suitable for concrete which has high alkalinity) and harmless to the environment.  (Source:- Cement, Concrete & Aggregates Australia- Colouring, Stencilling & Stamping Concrete, June 2007).

Pigment Dose Rates

The specified CCS concrete colour and its intensity is achieved by a pre-determined pigment dose rate per cubic metre of grey or off-white cement.  This rate efficiently disperses enough oxide pigment to colour the cement.

Thorough mixing of the concrete then disperses the CCS oxide pigment to ensure full colour and uniformity.

The amount of pigment required will generally be 3-8% of the weight of the cement in the mix.

Colours

Most colours (reds, yellows, browns and blacks) are oxides of iron. Some colours such as blue, green and white may be more expensive due to the more involved manufacturing process required to produce these special metal-oxide pigments.

The colour of the cement and fine aggregates affects the final colour of the concrete.  Grey cements and off-white cements will tint differently.

Colour oxides in off-white cement will always appear brighter in off-white cement than in grey cement, particularly with lighter blues and yellows.

However, when using blacks, dark red and brown pigments there is little or no difference in colour variance when using either base.

If a lighter, brighter colour is desired the use of an off-white cement base should be considered.

It is also important to note that cement colour and raw materials vary between suppliers. Therefore, all cement needed for a project should come from a single source if colour consistency is important.

Ensuring Uniform Colour

For uniform colour, every aspect of the concrete proportioning, mixing procedure, method of placement, finishing and curing should be consistent. If an exact colour match from batch to batch is difficult, borders of different colours, concrete pavers or other materials can be used to divide large areas into smaller more manageable sections which can be placed from a single batch.  This helps to mask any minor colour variations and can create acceptable patterns. (Source:- Cement, Concrete & Aggregates Australia- Colouring, Stencilling & Stamping Concrete, June 2007).

Water/Cement Ratio

To achieve consistent coloured concrete, the specified water:cement (w/c)ratio in concrete must remain consistent. Changes in the w/c ratio from batch to batch of concrete may result in colour variation.

If concrete is diluted on site by the unauthorised addition of uncontrolled water the concrete will experience lower hardness, strength and durability.  It can also result in paler and/or mottled colour variations in the concrete.

Concrete which has been water weakened will have lower strength, be less hard and wear resistant, easily erodible, more absorbent and permeable to water, degrading chemical solutions and other liquids, more likely to suffer rusting of its steel reinforcement to cause concrete cancer and be subject to greater shrinkage and therefore will be more likely to crack in places other than under the tooled or sawn joints, which visually disguise cracks.

Effects of Pigments on Concrete

Mineral oxide pigments have a negligible effect on concrete strength. In many cases, mechanical strengths are increased slightly - particularly at the same water:cement ratio.

Synthetically produced powder pigments such as CCS Pigments, are preferred to natural versions of pigments due to their uniformity and colour strength.  They are also more economical.

Test Samples

As mentioned above, the properties and raw materials within concrete will vary between suppliers and in order to minimise colour variation, the cement, aggregate and especially the pigment should be specified to be supplied from single sources.

We highly recommend project test samples are made in the desired CCS pigment colour(s) and the concrete mix that will be used.

Australian Standards

Coloured concrete applications should be specified with the prefix S for Special Class concrete to AS1379-2005-The Supply of Concrete and AS3600-2005 Concrete Structures. AS3610-1999 Formwork for Concrete provides guidance for the colour and quality of finish assessment of standard grey coloured, un-pigmented concrete, bound with grey cement. It may however be considered a useful base to establish the core specification for coloured concrete using pigments, as denoted in this Standard by the suffix C.

(Source:- Cement, Concrete & Aggregates Australia- Colouring, Stencilling & Stamping Concrete, June 2007).

Rich CCS powder pigments are made of high-quality metal oxides recycled from iron and steel or refined from the earth and are specially processed for mixing into concrete. They are manufactured to strict Quality Assurance guidelines certified as complying to ISO 9001.

CCS UV resistant mineral oxide pigments comply with ASTM C979-1999 Pigments for Integral Colouration of Concrete and Mortars, British / European Standard BS EN 12878-1999 Pigments for Portland Cements and Portland Cement Products and Australian Standard Colour Pigments For Use with Portland Cement ASK54-1935.

Special Disintegrating Packaging

CCS Pigments are packaged in special bio-degradable paper sacks which are simply added into the concrete mix without having to be opened or poured. The sacks disintegrate when water saturated and are fully mixed into the concrete - leaving no bags to dispose of into the environment.

View Application Guidelines or Full Specifications.