Final answer:
The statement is true because smaller coarse aggregates have a greater surface area that requires more cement to properly coat the aggregate for adequate bonding within the concrete.
Step-by-step explanation:
The statement 'For a given water-cement ratio, more cement is needed as coarse aggregates get smaller' is true. The surface area of smaller aggregates is greater, requiring more cement to coat the surface area for adequate bonding and a strong cement matrix. Coarser aggregates have a smaller surface area relative to their volume, so they require less cement paste to cover them adequately, assuming that the water-cement ratio is kept constant. Therefore, if you are working with smaller coarse aggregates, you'll need to increase the amount of cement in the mix to maintain the water-cement ratio and achieve the desired workability and strength in the concrete.