Fine aggregate is material that will pass through a 4mm sieve. Generally fine aggregate is a naturally occurring sand material, crushed rock material, or a combination of both. The distribution of particle sizes, known as grading, is important because it effects some properties of the plastic concrete, e.g. water demand and bleeding. A uniform distribution of particle sizes is preferable.
Coarse aggregate will not pass through a 4mm sieve. Typically, nearly half the weight of concrete will be coarse aggregate. The nature of the coarse aggregate can have a marked effect on properties such as strength, shrinkage, thermal expansion. Coarse aggregates can be classified according to type.