In general, the most appropriate size of aggregate used in the RCC structure is 20 mm. Natural river sand is usually used as a fine aggregate, but in places where it is not economically available, finely crushed stone can be used instead. Aggregates are used in concrete to provide savings in cost and do not react with cement and water. The size of coarse-grained aggregates is the primary factor in determining the strength of concrete, with 20mm aggregates meeting the threshold for strong concrete and 40mm aggregates for normal strength concrete.
Since fine aggregates are used to fill the voids of coarse-grained aggregates, the smaller the coarse-grained aggregates, the finer the fine aggregates should be. They increase the workability of concrete. In large aggregates, the surface area to be wetted per unit weight is smaller, and the water-cement ratio is lower, which increases strength. All kinds of aggregate made of igneous rock crushed from igneous rock, granite rock, sedimentary rock and metamorphic rock can be used for different purposes in construction.
For medium strength concrete, 40mm aggregates should be used, while 20mm is best for high strength. However, due to limitations in mixing, handling and placing equipment, the size of the aggregate cannot be increased to any limit. Aggregates must not contain any harmful materials in such a quantity as to affect the strength and durability of the concrete.