USES OF THE LIGHT WEIGHT AND HEAVY WEIGHT CONCRETES.

For special purposes light weight concretes are being used .A variety of light weight aggregates consist of pumice or cinders used for insulating concretes , processed aggregates like expended shales ,clays ,slates slags or pelletized fly ash for structural light weight concrete .These are light in weight due to the individual aggregate particles are porous or cellular which is achieved by using gas or steam in processing the aggregates in rotary kilns at as high temperature as 1100degree C .Three classes of light weight concretes are (1) Low density concretes which are employed for insulation with unit weight not exceeding 800 N /cubic metre. (2) Moderate strength concretes with unit weight from 9500 N/ cubic metre to 1300.N / cubic metre having compressive strength of 7 N / mm square to 15 N/square chiefly used as fill .(3)Structural concrete with unit weight of 14000 N/ cubic metre to 19000 N/cubic metre and compressive strength equal to those of the stone concretes .Heavy weight concretes are required for shielding gamma and X - radiation in nuclear reactor and similar installations, for protective Structures, as counterweight of the lift bridges . Heavy aggregates such as heavy iron ores or barium sulfate Rock crushed to suitable sizes .Steel in the form of scrap , punching or fines is also used .Unit weight of the heavy weight concretes with natural heavy rock aggregates range from 30000 to 32000 N/cubic metre. If iron punchings are added added to high density ores unit weight can be as high as 38000 N/ cubic metre.The weight may be as high as 52000 N/ cubic metre if ores are used for the fines and steel for coarse aggregate.