Special Type of Concrete - Heavy Weight Concrete

Dnyan Deshmukh

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Sep 7, 2017
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Special Type of Concrete - Heavy Weight Concrete

Requirement for Heavy weight concrete:

Nuclear reactors require shielding against radiations that emanate from atomic reactions in order to protect the outside environment. High density concrete (heavy concrete) produced using hematite (an iron ore) aggregate has is the most economical and effective shielding material that is extensively used in Indian Nuclear Industry.

Composition of Heavy Concrete:

Heavy concrete is composed of aggregate made from hematite (an iron ore), cement, and water. Alike normal concrete, in order to obtain the desired properties required for production and easy placement, chemical admixtures are used. Ice is used to replace whole or part of mixing water to obtain the desired placement temperature in hot weather concreting.

Hematite:
Hematite in India is mainly found in two areas (Bellary in Karnataka, and Jaipur in Rajastan).

Owing to high specific gravity of hematite ore (4.9) as compared to normal aggregate (2.7 to 3.0) mining of the ore requires additional physical effort. Crushing of mined ore to obtain aggregate of the desired size also causes very high wear of crusher components (Blow bars that last for 40, 000 MT of normal stones wear off while crushing 2000 MT of hematite). The same crusher and screening units used for normal stones can be used in the production of heavy aggregate.


Concrete mix proportion:

A typical heavy concrete mix that has a density of 3800 kg/Cum, capable of being placed by concrete pumps is as follows (Quantity of ingredients in kg per cubic meter of concrete is specified):

Cement = 335 kg

Heavy Coarse Aggregate (20mm to 4.75mm) = 1872 kg

Heavy Fine Aggregate = 1179 kg

Crushed Sand (Normal) = 168 kg

Water+Ice = 173 kg

Admixture (Retarding Superplastisicer) = 4.68 Lit.

Microsilica = 25 kg



Production & Placement of heavy concrete:

Production process of heavy concrete is similar to that of normal concrete. Since the density of heavy concrete is high, the quantity of one batch that can be mixed in a batching plant need be reduced in proportion to the density of heavy concrete to normal concrete. Generally 0.6 Cu.m. of heavy concrete is produced in a mixer of normal capacity of 1 Cum For the same reason transit mixers also need be under-loaded.

Heavy concrete exhibits the property of segregation and hence care need be taken in transportation and placement. In order to make the concrete capable of being pumped, micro-silica has been added. However heavy concrete is pumped at a slow rate and causes faster wear of pipes.


Special Heavy Concrete:

In restricted areas, for enhanced radiation shield, steel balls (0.5mm to 5mm) are used in heavy concrete. The density of such concrete is as high as 4100 kg / Cu.m. Production and placement of this concrete is extremely difficult. Special heavy concrete should be necessarily placed manually or by crane and bucket (this cannot be pumped).