Which statement about the effect of sand content on water demand is correct?

Which statement about the effect of sand content on water demand is correct?

• A. Increasing sand decreases water demand
• B. Increasing sand increases water demand
• C. Sand content has no effect on water demand
• D. Water demand is only affected by cement content

Answer: (B)

Increasing sand in the mix raises the surface area that needs to be wetted by the cement paste. More surface area means you must add more water to achieve the same workability, so the water demand goes up. Sand also can absorb water, especially finer sands, which further increases the amount of water required to maintain the desired slump. The idea that sand content has no effect or that only cement content controls water demand isn’t accurate because the fine aggregate directly affects how much water is needed to coat and lubricate all particles.

Increasing sand in the mix raises the surface area that needs to be wetted by the cement paste. More surface area means you must add more water to achieve the same workability, so the water demand goes up. Sand also can absorb water, especially finer sands, which further increases the amount of water required to maintain the desired slump. The idea that sand content has no effect or that only cement content controls water demand isn’t accurate because the fine aggregate directly affects how much water is needed to coat and lubricate all particles.