Hand Mixing Of Concrete
The process of mixing the various ingredients of concrete by manual labour, is called hand mixing of concrete. Hand mixing of concrete may be resorted to at small projects which require limited quantity of concrete. Now-a-days machine mixing of concrete is almost done and only in exceptional cases, mixing concrete by hand may be permitted. It may be noted that in hand mixing more cement is required as compared to machine mixing of concrete for obtaining the concrete of same strength. Method of mixing concrete by hand may also be necessitate if the mixer fails to work due to mechanical defects and concreting operation is to be completed. The hand mixing of concrete may be done as detailed below:
(i) Depending upon the quantity of concrete to be mixed, either construct a suitable platform of bricks with lean concrete or obtain iron sheets of suitable size.
(ii) Spread the required quantity of fine aggregates (sand) on the platform and then spread the required quantity of cement uniformly over the sand layer.
(iii) With the help of shovels, mix the sand and cement in dry state till a mixture of uniform colour is obtained.
(iv) Spread the sand cement mixture once again uniformly on the platform and then spread the required quantity of the coarse aggregates and mix the mixture in dry state thoroughly.
(v) On obtaining a uniform coloured mix with sand, cement and coarse aggregates, make a depression in the centre of the mixed materials.
(vi) Add 75% of the required quantity of water (based on the water-cement ratio) in the depression and turn the mix towards the middle, with the help of hands or shovels. The mixture is mixed thoroughly till a uniform colour and consistency is obtained.
(vii) Add the remaining quantity of water and continue the mixing process till a concrete of uniform consistency is obtained.
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