Explanation: The materials of concrete should be mixed thoroughly so that there is a uniform distribution of materials in the mass of concrete. The thorough mixing also ensures that water cement paste completely covered the surface of aggregate.

Explanation: The mixing by hand is allowed in case of small works on unimportant work were small quantity of concrete is required. For important work, if hand mixing is to be adopted, it is advisable to use 10% more cement than specified.

Explanation: It is found that the materials of concrete with the help of machine is more efficient and it produces concrete of better quality in a short time. The mixtures of various types and capacities are available in the market. They are may either be of tilting type or non tilting type.

Explanation: The type of equipment to be used for transport of concrete depends on the nature of work, height above the ground level and the distance between the points of preparation and placing of concrete. For important words, the various mechanical devices such as dumpers, truck mixer, conveyor belts, etc. may be used.

Explanation: The main aim of consolidation of concrete is to eliminate air Bubbles and thus to give maximum density to the concrete. The importance of consolidation of concrete can be seen from the fact that a presence of 5% of voids reduces 30% strength of concrete.

Explanation: The difference between voids and pores may be noted. The pores represent the opening within the individual particles. The process of consolidation of concrete can be carried out either by hand or by means of vibrators.

Explanation: The Hand Method require use of a fairly wet concrete. It should however be remembered that wherever feasible, the hand competition should be preferred because the use of vibrator may lead to the segregation of the aggregates.

Explanation: The Internal vibrators or Immersion vibrators should be inserted and withdrawn slowly and they should be operated continuously while they are being withdrawn. In this, the Steel Tube is called poker and it is connected to an electric motor or a petrol engine through a flexible tube.

Explanation: Surface vibrators are used to finish concrete surface as a bridge floors, roads slabs, station platform, etc. These vibrators are found to be more effective for compacting very dry concrete mixes because the vibration acts in the same direction of gravity and the concrete is compacted in the confined zone.

Explanation: In Form or Shutter vibrators, the Vibrating action is conveyed to concrete through the formwork. A considerable energy is absorbed by the formwork during transmission of vibration. Hence they are not generally used.