Question

Suppose you are specifying white architectural concrete. Which of the following statements are true?

A. A high proportion of sand in a white concrete mix is recommended to help reduce color variations.
B. A high proportion of sand in a white concrete mix is recommended to help prevent “bug holes” (small round cavities that result from air trapped at the form surface during placement).
C. Manganese oxide pigment is sometimes used to intensify the whiteness of white concrete.
D. The formwork materials can affect the concrete color.

Answer

A. True — Light-colored sand acts as a pigment in cement paste.
B. False — High sand content increases the likelihood of bug holes.
C. False — Materials containing iron and manganese oxides produce gray colors. Titanium dioxide is often used as a white pigment additive at 1 to 3 percent by weight of concrete.
D. True — Generally the more water absorbed into the formwork face, the darker the concrete. If color control is desired, use nonabsorbent form surfaces or linings.