Aggregate classification is generally based on its size, petrographic characteristics, weight, and source. Size classification ranges from coarse to fine aggregates, defined by the size of the particles. Coarse aggregates are particles that do not pass through ASTM sieve No. 4, and aggregates that pass through the sieve are fine aggregates.
Petrographic classification groups aggregates based on common mineralogical characteristics. Some of the common mineral groups found in aggregates are silica minerals, feldspars, micaceous minerals, and carbonate minerals.
Aggregates are categorized by weight into normal-weight, heavyweight, and lightweight types. Normal-weight aggregates are typically used in standard concrete applications. Heavyweight aggregates are used to produce denser concrete, and lightweight aggregates are used to make concrete for thermal insulation purposes.
Aggregates harvested from rock quarries and sourced from gravel pits and riverbeds are natural aggregates. In contrast, aggregates synthesized from industrial byproducts, such as fly ash and expanded blast furnace slag, or recycled by crushing construction waste, are typical examples of artificial aggregates.
