Mixing:

Thorough mixing of the materials is essential for the production of uniform concrete. The mixing should ensure in which the mass becomes homogeneous and uniform within color and consistency. There are two techniques adopted for mixing concrete.

Hand Mixing

In this method, ingredients are mixed in dry state three times on a watertight platform to avoid loss of water from the mix. Then water is added in correct quantity and wet mixing is done thoroughly till concrete becomes uniform in colour and consistency. Generally, 8 to 10 % extra cement is added for hand mixing.

Machine Mixing

It ensures a better and uniform mixing of concrete ingredients. It produces concrete of better quality at a faster rate and at less cost more efficiently. Now-a-days, concrete mixers are very common. Even for small jobs mixers are preferred. Following are the types of mixer.

(a)        Drum type

(b)       Pan type

(c)        Paving mixer

(d)       Transit mixer

(e)        Tilting kind - 85T, 100T, 140T, 200T.

(f)        Non-tilting kind - 200NT, 280NT, 340NT, 400NT, 800NT.

(g)       Reversing - 200R, 280R, 340R, 400R.

Number indicates the quantity of materials in litres in one batch.