Lightweight aggregates are used to make lightweight concrete. They are obtained from natural sources, and manufactured from waste or byproducts.
Most lightweight aggregate is produced from materials such as clay, shale, or slate. Blast furnace slag, natural pumice, and vermiculite and perlite can be used as substitutes, however. To produce lightweight aggregate, the raw material (excluding pumice) is expanded to about twice the original volume of the raw material. The expanded material has properties similar to natural aggregate, but is less dense and therefore yields a lighter concrete product.
Of special interest is lightweight aggregate produced from coal ash. The ash is pelletized and sintered to produce the product. For information on the process and the properties of the product click the hot link.
The strength of a lightweight aggregate is directly related to its particle density, since the percentage of voids in an aggregate particle largely determines its strength. An aggregate’s relative density should be less than 2 to qualify as ‘lightweight’ and it should be at least 1.2 for the aggregate to be suitable for use in structural lightweight concrete.
