Managing Concrete Color

• The color of cement used in a concrete mix has the greatest impact on the final appearence of the concrete. Portland cement is available in both white and grey variations.
• Concrete mixes using white cement and pigment will yield colors that range from pastel, at low pigment loads, to paint-like colors when higher doses of pigment are used.
• Concrete mixes using grey cement will yield muted concrete colors ranging from light grey to richly saturated earth tones.
• While white cements must meet specific ASTM standards for color consistency, there may / will be variations in color between individual bags, batches, and manufacturers.
• Grey cement is not required to meet any ASTM standards for color consistency and can vary from grey with cool blue or green tones to warm brown tones.
• Other elements of the mix (sands and large aggregate) will have less of an impact when managing concrete color.

Step 2 – Pigments and Coloring

• Integral color in concrete is achieved by incorporating pigments into the concrete mix design. Unlike topical stains, which are applied only to the exposed surface, integral pigments color the concrete throughout.
• Concrete pigments are classified into two groups – synthetic oxides and organics.

  Synthetic Oxides – Pigments made from oxidized metals and valued for their stability. For example oxidized Iron yields shades of red, yellow, black, and brown. Chromium yields shades of green and Titanium gives us white. Synthetic oxides are available in either powdered or liquid form.

  Organics – Pigments made from organic compounds and valued for their bold tones. For example, carbon black is perhaps the most common organic pigment used in the production of concrete. However, these pigments are not recommended for all applications as they are comparatively unstable and do not meet lightfast (fading) requirements.

Step 3 – Pigment Terminology

• Pigment Loading defines the amount of pigment in the concrete mix relative to the amount of cement. A mix design with 100 lbs. of cement requiring a 10% loading of Iron Black would require 10 lbs. of Iron Black.
• It is important to remember that the pigment loading is based on the amount of cementitious material only, not the total aggregate of the concrete.
• Supplemental materials such as fly ash, silica fume, and slag would be included in the cementitious materials calculations.

Step 4 – Pigment Loading

• Expressed in percentage format, the pigment load refers to the color intensity.

  Example: A concrete mix design containing a 2% load of Iron Black will result in a lighter, less saturated color than the same concrete mix design containing a 5% load of Iron Black.

Step 5 – Saturation

• Saturation is a term used to describe the load point at which additional pigment will not affect the finished color of the concrete.
  • Example: At approximately 5% loading of Carbon Black, the mix design is saturated. Adding additional pigment above the saturation point will only serve to waste pigment.

Step 6 – Load Limits

• Pigments affect the structural performance of any mix design and must be used judiciously.
  • Structural concrete can safely be loaded up to 10% and decorative non-structural concrete can go as high as 15% loading. Under no circumstances should concrete loads exceed 15%.

Step 7 – Pigment Formulation

• Pigment formulations are blends of base pigments commonly expressed in percentages of each color component (i.e. red, yellow, black, white) of the total pigment.
• An example of a pale green formulation would look something like this — 30% Green + 70% White. Stated by weight: a 10 pound batch would contain 3lb of Green and 7lb of White.
• A dark blue formulation could be — 65% Blue + 25% Red + 10% Black. Stated by weight: a 30lb batch would contain 19.5lb Blue, 7.5lb Red, and 3lb Black.