5.9 : Aggregates Classification

Aggregates constitute nearly three-quarters of the total volume of concrete and are classified based on their size, source, composition, and weight.

Based on the size, aggregates retained on the ASTM No.4 sieve are classified as coarse aggregates, while those passing the sieve are classified as fine aggregates.

Based on the source, natural aggregates include crushed stones obtained from rock quarries, gravel extracted from gravel pits, and sand mined from riverbeds.

Some artificial aggregates are produced by spraying water on molten blast furnace slag to form expanded blast furnace slag, heating clay in rotary kilns to form expanded clay, or crushing demolished concrete.

Quartz, feldspar, mica, and calcite are some commonly found mineral compositions in natural aggregates, depending on the type of parent rock from which it is derived.

Lastly, based on weight, the aggregates are classified as normal-weight, heavyweight, and lightweight.

Normal-weight aggregates are commonly used in standard concrete construction, heavyweight aggregates are used to produce dense concrete for radiation shielding, and lightweight aggregates are employed to create lightweight concrete for applications requiring reduced structural load or improved thermal insulation.