The usual range of aggregate used in construction is between 9.5 mm and 37.5 mm in diameter, with the most common size being 20 mm. Coarse-grained aggregates are particles larger than 9.5 mm. A larger size, 40 mm, is more commonly used in bulk concrete. The size of the aggregate affects the elastic and thermal properties of concrete, as well as its dimensional stability.
Aggregates are one of the most important components of concrete that give it body and reduce shrinkage. The larger size of 4.75 mm is coarse-grained sand or aggregate, with sizes ranging from 5 mm to 256 mm or more. Alternative sources of aggregates or additional aggregate mixtures can be considered to approach the ideal gradation that provides the best workability, pumpability, shrinkage reduction, and economy. The fundamental relationship between the water-cement ratio and strength begins with the correction of the contribution or absorption of moisture by aggregates.
In a mass concrete or PCC work, the use of larger aggregates will be useful due to the lower consumption of cement, which will also reduce the heat of hydration and the corresponding thermal stresses and shrinkage cracks. Leveling limits and maximum aggregate size are specified because these properties affect the amount of aggregate used, as well as cement and water requirements, workability, pumpability, and concrete durability. But in practice, the size of the aggregate cannot be increased to any limit due to limitations in mixing, handling and placing equipment. Using larger coarse-grated aggregates generally reduces the cost of a concrete mix by reducing requirements for cement, the most expensive ingredient.