Effect of Grey Cement on Final Colour
Technically the grey colour of the cement can be equated to a weak black pigment which when added to the colour of the pigment used, will produce a new blend.
It follows that if the colour of the cement changes, then the resulting colour of the final blend will be different.
White cement will give best results for lighter colours.
Grey cement will give best results for darker colours.
Limestone will lighten the colour of the mix.
Lighter tone sand will give best results.
The colour of the aggregates, sand and stones will have its own effects, although to a much lesser extent.
Mixing Cycle For Coloured Concrete
When cement, water and iron oxide pigment are present together, water is preferentially absorbed by the cement leaving the pigment in a semi dry stage. This state encourages the clumping together of the pigment particles forming dry balls. This condition of "BALLING" will not breakup totally during the short mixing cycle of the concrete. Large balling creates defects in the product but tiny balling, although imperceptible to the eye, do decrease the overall effectiveness of the pigment. Balling can be easily avoided by using the proper cycle in introducing the pigment into the concrete mix.
The principle of a good concrete mixing cycle is the total spreading of each interacting component before the next one is added. When pigment is introduced into the mix, regardless of where in the cycle it is added, it should be allowed to mix uniformly with the present components before the next step begins. Once spread uniformly, the particles will not clump being forced apart by the other components in the mixer. It is of interest to note here that the cement may also clump together if it is not uniformly spread before water is added.
Based on the above principle, the following cycle emerges as the most efficient way to achieve desirable and optimum results.
Preferred cycle: