Artificial aggregates can also be used in concreteproduction. Utilization of waste material such as using recycled concrete orbrick as aggregates is becoming general, and fly ash is used to replace fineparticles. Also the by-product of the iron industry blast-furnace slag has beenwidely used in concrete production. Expanded clay aggregates are used toproduce expanded clay light-weight concrete, also expanded shales, slates,perlites and slags are used. Properties of expanded clay aggregates differ fromnatural aggregates, grains absorb water and they crush easily for exampleduring mixing.
Also proportioning of expanded clay light-weight concrete isvery different from normal concrete. Pelletized, air-cooled and granulatedblast furnace slag can also be used, but the use is limited. (SuomenBetoniyhdistys, 2005a, 32.
)Perlite is one of the artificial lightweightaggregate. It is an amorphous volcanic glass which is formed by the hydrationof the extrusive igneous rock and has relatively high water content. The processof hydration is occur naturally and it will expand greatly when it is heatedsufficiently. When it is crushed and heated to temperature above 15000 F, itwill expand to form lightweight, glass-like particle structure, andnoncombustible structure. The weight of perlite is about 1/10 weight of graveland sand with white or grey in color.
It is used in lightweight fire retardantfor plaster , floor fills, roof, curtain walls , and precast panel, andinsulating concrete.Vermiculite is a silicate and hydrous mineral thatexpand greatly when subjected to heat. It is formed by hydrothermal andweathering alteration. The vermiculite concrete is about 15 % of the weight ofthe structural grade concrete. It also has good insulating properties and hasfireproofing characteristics. The vermiculite concrete also being used asprecast concrete units like structural slabs with core type, channel slab,double tees, and pre-stressed single.
The cast-in place vermiculite concreteprovides a smooth surface of built up roofing membrane.Norlite is a porous ceramic material that is formed byexpanding the selected shale in a rotary kiln. The product of the process isproduce a consistent and high quality of ceramic aggregate which has propertiesof a strong, durable, physically stable, lightweight, environmentally inert,and good thermal insulation. It is also absorptive aggregates, non-toxic and itwill not degrade over time. Norlite has the advantages of reducing dead loads,improving fire rating, and lower the thermal conductivity of element inbuilding.