Most concrete used in slabs on ground has coarse aggregate with a maximum size of:

• A. 3/8 inch
• B. 1/2 inch
• C. 3/4 inch to 1-1/2 inch
• D. 1 inch

Answer: (C)

In slabs on grade, the size of coarse aggregate is chosen to keep the concrete workable, properly consolidatable, and able to finish smoothly over the subgrade. The typical maximum coarse aggregate size used in these slabs falls in a range from 3/4 inch up to 1-1/2 inches. This range accommodates different slab thicknesses and load requirements: too-large aggregate makes placement and compaction difficult, can leave voids or honeycombing, and roughens the surface, while too-small aggregate increases cement content and cost without providing additional finishing benefits. For most residential or light-duty slabs, 3/4 inch is common, while heavier-duty slabs may use up to about 1-1/2 inch to balance strength, workability, and finishability.