Which statement about supplementary cementitious materials (SCM) is true according to the given data?

• A. SCMs allow increasing the free water by 20 pounds per 100 pounds of cementitious material above 550 pounds per cubic yard
• B. SCMs cannot be used with cement
• C. SCMs must replace cement entirely
• D. SCMs have no effect on water content

Answer: (A)

When SCMs are used, they can change the mix’s workability and how much water is effectively needed. The data provides a specific allowance: if the total cementitious material per cubic yard exceeds 550 pounds, you may increase the free water by 20 pounds for every additional 100 pounds of cementitious material. This helps maintain the desired slump and workability without compromising the mix, despite the different behavior of SCMs compared to plain cement.

For example, with 650 pounds of cementitious material per cubic yard, you’re 100 pounds over the threshold, so you may add 20 pounds of free water. With 750 pounds, you may add 40 pounds, and so on. This rule directly reflects the stated data about water content adjustment when SCMs push the cementitious content beyond 550 pounds per cubic yard.

SCMs are designed to be used alongside cement and often partly replace it; they do affect the water demand and overall mix behavior. They do not require replacing all cement, and they do have an impact on water content, so the other statements don’t fit the data.