IS 456- 2000 recommends that mixing should be done in a mechanical mixer. The mixing should be continued till all the materials are uniformly distributed in the mixer and the end product is of consistent colour. Mixing time should be atleast 2 min. Concrete should never be mixed just on the ground, otherwise dirt will also get mixed in. While mixing the raw materials, cement and sand should be intimately mixed first, then the coarse aggregates. Water is added last and the mixture should be turned over until a uniform colour is obtained all around.