Concrete construction has benefited in many ways from the predictable set control, greater uniformity, higher strengths and other controls of concrete performance now possible. Concrete also offers another performance feature: a unique range of control of its physical properties its weight, density and other properties inherent in the material itself. This control is usually dictated by owner needs and is a response by the concrete industry to customize the construction material to provide exactly the performance desired in the hardened state.
Concrete is heavy typically about 150 pounds per cubic foot. In some cases, such as dams, radiation shielding, retaining walls and foundations, this is a substantial advantage. In many applications, such as slabs-on-grade, it may be of little consequence. However, for certain applications, such as structural floors in high-rise buildings, it is highly desirable to lower the weight of concrete while retaining its strength to lessen dead load. This article briefly reviews some of the most widely used ways in which concrete's physical properties are varied, including: structural lightweight concretes, fill and insulating concretes, heavyweight concretes, polymer concretes, fibrous and other concretes.
Heavyweight concretes are usually used for radiation shielding or counterweights. These can range from 200 pounds to about 400 pounds per cubic foot. They are produced by using special heavy aggregates of natural and synthetic materials, such as barite, ferrophosphorous, goethite, hematite, ilmenite, limonite, magnetite, steel punchings and shot, hydrous-iron ore, serpentine and bauxite. The water content of concrete also is important in shielding certain forms of radiation, namely neutrons.