Why Concrete is Gray?

The colors around us are a result of how materials absorb and reflect light. Materials that fully absorb all the light they come in contact with appear black to humans, while those that only reflects what is bounced back from other objects look white. When light interacts with a material, it does not always look the same. Depending on what type of interaction is taking place determines whether the beam of light will be reflected or absorbed. The result can range from pure white to dark black-and-white contrast in between any color imaginable.

It’s time to go a little more in-depth on the science of concrete. What is it about this substance that causes such an unusual effect? Which constituent part could cause this particular hue? We know that when we mix cement, water, and some particles together; all things considered, they’ll produce something grayish looking…but which components are causing these effects specifically?

Cement is made up of four unique mineral phases: two calcium silicates, a calcium aluminate, and a mixed crystal known as Calcium Aluminate Ferrite (C4AF). While the first two minerals are naturally white in color; C4AF appears brownish due to its high iron concentration. This natural coloring comes from oxidizing agents that create this telltale tint which only lasts for about six months before it starts reverting back to its original grey-white hue. Have you ever wondered why concrete is typically colored grey? It’s not because it was mixed poorly, or that the cement supplier ran out of brown dye. The truth is much more interesting: magnesium in C4AF polluted with this colorless additive makes a final product that looks like stone, especially when polished to perfection.