Why is aggregate grading important in concrete mix design?

Proper aggregate grading ensures optimal packing density, minimizing voids and cement paste requirement. Well-graded aggregates (continuous distribution of sizes) produce workable, economical concrete with good strength. Grading zones classify fine aggregate from coarser (Zone I) to finer (Zone IV). Gap-graded mixes (missing intermediate sizes) require more paste but may be used for exposed aggregate finishes. Fineness modulus summarizes grading (higher = coarser). Proper grading reduces segregation, bleeding, and permeability.