Aggregates Sand and gravel, on account of their natural colors, also have an effect on the shade of the finished concrete. Likewise, the granular composition of the sand can have an effect on the shade under certain conditions, namely when the sand contains a high proportion of fines. The higher the proportion of fines in a sand, the less pronounced the tinting strength of the pigment used. Because there is generally very little fluctuation in the composition of sand from the mine, especially in terms of the quantity of fines, there is very little risk that it will cause differences in shade, although to be on the safe side it is one more aspect that deserves consideration.
Water/cement ratio and shade of the concrete Have you ever wondered why the head on a glass of beer is white while the beer itself has a golden color? The foam consists of lots of little air bubbles that scatter the light in the same way that white pigments do. This little digression is relevant because it explains the relationship between the shade of the concrete and its water/cement ratio. The excess mixing water evaporates from the concrete and leaves behind cavities in the form of fine pores. These pores then act like the bubbles in the foam on a glass of beer. They scatter the incident light and thus give the concrete a brighter appearance. Therefore the higher the water/cement ratio, the lighter the color of the concrete. As the following photograph illustrates, gray concrete to which no pigment has been added obeys this law just as colored concrete does. Fig 12. It is clear from the illustrated examples that consistency in the specified water/cement ratio is of great importance in achieving a uniform and consistent perceived color.
Fig. 10: Influence of the color of the cement on the shade of the concrete Fig. 12: Influence of the water/cement ratio on the shade of the concrete
Fig. 11: Influence of the color of aggregates on the shade of the concrete