General name of materials such as sand, gravel and crushed stone used in concrete production is aggregate. Aggregate, occupying about 60-75% by volume in concrete, is an important component. Aggregates are divided into two; fine aggregates (sand, crushed sand, etc.) and rough aggregates (gravel, crushed stone, etc.).
 
The most important characteristics of aggregates are:

• ♦ They must be hard-wearing and free from cavities,
• ♦ They should not contain poor particles (sea shells, wood, coal pieces, etc.),
• ♦ They must be resistant to pressure and abrasion,
• ♦ They must not contain substances that can cause damage to dust, soil and concrete,
• ♦ They must not contain flat and long grains,
• ♦ They must not go in alkali reactions.
• ♦ Sieve analysis, flatness, specific gravity and water absorption in concrete aggregates should be followed at appropriate intervals to monitor quality continuity.