What purpose does the aggregate serve in structural grout?

• A. The aggregate provides load transfer and increases wall strength.
• B. The aggregate reduces strength and increases shrinkage.
• C. The aggregate makes grout impermeable.
• D. The aggregate prevents flow completely.

Answer: (C)

In structural grout, adding aggregate creates a denser matrix that blocks capillary pathways and fills voids in the cement paste. This reduces the grout’s ability to allow water to flow through, which is the main hydraulic benefit you’re looking for. By interrupting the continuous pores in the paste, the aggregate greatly decreases permeability, helping protect embedded steel and improve durability in masonry. While it won’t stop flow completely in all conditions, the reduction in water movement is the key reason aggregate is used in grout.