Normal weight aggregates, used for most concretes, are naturally occurring gravels from land or marine sources, or crushed rocks, for example, limestone, granite or basalt.
Lightweight aggregates are artificially produced aggregates of low density, e.g. sintered pulverised fuel ash (e.g. Lytag), expanded clay or shale (e.g. Lica or Liapor), or natural lightweight materials, such as pumice.
Heavy weight aggregates are used for concretes with higher than normal densities (e.g. those used for radiation shielding or ballast purposes). Generally these are naturally occurring dense rocks such as barytes, magnetite and other heavy metallic ores. Alternatively, metal aggregates, e.g. steel or iron shot, may be used.