Lightweight aggregates possess a lower bulk density compared to normal aggregate, lightweight fine aggregate bulk density is less than 70lb/ft3(1120kg/m3), lightweight coarse aggregate possess a bulk density less than 55lb/ft3(880kg/m3). a lightweight aggregate first major application in high rise building was in 1929, 28-story South Western Bell Telephone in Kansas City of which the upper 14 stories were of lightweight concrete
There are several methods for producing lightweight aggregates such as expanding, pelletizing, sintering of products such as furnace slag, clay, shale, slate and fly ash. shape and texture of lightweight aggregate depend on the method of production, the shape can be cubical, angular, rounder and irregular, texture can range from smooth surface to highly irregular surface with large pores. aggregate shape and texture will influence concrete properties and also it will play a major role in determining the concrete mix workability along with other factors such as W/C, cement content, coarse aggregate, and fine aggregates content.
The use of lightweight aggregate has potential advantages such as
- using lightweight aggregate will reduce concrete weight, this will reduce structure dead weight. as a result of the reduction of the dead weight of a structure, size of structural members, structure foundation and amount of required reinforcement will be reduced.
- lightweight aggregate produced from industrial waste, therefore it helps in preserving the environment by recycling waste material and reducing the severe depletion of earth resources.
- lightweight aggregate possesses a lower thermal of expansion coefficient compared to normal weight aggregate, this, in turn, will reduce the thermal movement and enhance structure durability.
- the lightweight aggregate has a lower permeability compared to normal aggregate, also it has a better resistance against freeze-thaw cycle compared to normal aggregate.