Aggregates make up 65-80% of concrete's volume and are inert fillers that float in the cement paste. Their characteristics impact the performance of fresh and hardened concrete. Aggregates are classified based on size, specific gravity, availability, shape, and texture. Proper aggregate grading leads to a dense, strong concrete mixture. The fineness modulus is a number that indicates an aggregate's grading, and the flakiness index measures elongated particles. Well-graded aggregates with low elongation produce high quality concrete.