Density of normal concrete is in the order of about 2400 kg.per cubic metre. The density of lightweight concrete will be less than about 1900 kg.per cubic metre. To call the concrete, as high density concrete, it must have unit ranging from about 3360 kg.per cubic metre to 3840 kg.per cubic metre, which is about 50% higher than the unit weight of conventional concrete. They can however be produced with the densities up to about 5280 kg.per cubic metre using iron as both fine and coarse aggregate. The high density concrete is used in the construction of radiation shields.

The advent of nuclear energy industry presents a considerable demand on the concrete technologists. Large scale production of penetrating radiation and radioactive materials, as a result of the use of nuclear reactors, particle accelerators, industrial radiography, and X-ray gamma ray therapy, require the need of shielding material for the protection of operating personnel against the biological hazards of such radiation. Concrete, both normal and high density are effective and economic construction materials for permanent shielding purposes.