Lightweight Aggregate Concrete:

Lightweight aggregates could be categorized into two categories namely natural lightweight aggregates and artificial lightweight aggregates.

Following are the examples of natural lightweight aggregates.

(a) Rice husk      

(b) Pumice

(c) Volcanic cinders      

(d) Diatomite

(e) Sawdust        

(f)  Scoria

Given below are the examples of artificial light weight aggregates.

(a) Thermocole beads   (b) Artificial cinders

(c) Expanded perlite     (d) Coke breeze

(e) Foamed slag           (f) Exfoliated vermiculite

(g) Sintered fly ash       (h) Expanded shales and slate

(i) Bloated clay.            

Natural lightweight aggregates are not found in many places. They are also not of uniform quality. Thus, they are not used widely in making lightweight concrete. Pumice is the only natural lightweight aggregate which is used widely.

Lightweight aggregate concrete is made by the use of lightweight aggregates. Different lightweight aggregates have different densities. Strength of lightweight concrete depends on the density of concrete. Less porous aggregate that is heavier in weight produces stronger concrete particularly with higher cement content. A grading of aggregate, the water-cement ratio and the degree of compaction also affect the strength of concrete. Lightweight aggregate concrete exhibits higher moisture movement than the normal concrete. Concrete while wetting swells more and while drying shrinks more. A coefficient of thermal expansion of concrete made with lightweight aggregate is generally much lower than ordinary concrete.