Mixing and Transportation of concrete, hand mixing, mechanical mixing

 Methods of mixing:-

Concrete is mixed either by hand mixing or by machine mixing based on the quantity of concrete required.

1. Hand mixing:-

• Mixing by hand is employed only for specific cases where quality is not of much importance, either because of the important nature of the work or because the quantity of concrete required is less.
• Hand mixing generally does not produce uniform concrete and hence should not be normally used, unless it is for every small domestic works.

2. Mechanical mixing:-

• Mechanical mixtures can be divided into two main types batch mixer and continuous mixers.
• Batch mixes produce concrete batch by batch, one batch at a time. The operation is intermittent. The raw material is loaded at one end and the concrete is discharged at the other end. This constitutes a cycle of operation which is repeated until enough quantity of concrete is produced.
• Continuous mixers produce concrete at a specified rate. The raw materials are continuously entered at one end and mixed concrete exits from the delivery end.

Transportation of concrete:-

The following methods are used for transporting concrete:-

1. Barrows:-

Manual wheelbarrows of approximately 80 kg capacity can be used for long horizontal distance.

Four major works, power barrows of 800 kg capacity, up to 300 m hauls are used.

2. Belt conveyor:-

It can be used when hauling concrete over long distances.

It is not very much recommended because of its well vulnerability to segregation. The initial setting up cost is also high. Discharge can be as high as 115 metre cube per hour.

3. Direct discharge in two forms by short shutes:-

Short shutes in a semicircular shaped stiffened at intervals are simple and economical to use.

Free fall of concrete from a height of more than 2 metre must be avoided.

4. Dumpers and trucks:-

These are used for horizontal long hauls. Because of jolting, especially if the terrain is rough, the concrete during transit has the risk of segregation

5. Elevating towers and hoist:-

In multi storey buildings, elevating towers are used for lifting concrete buckets. The lifted concrete is then distributed by either shutes or barrows. This type of transportation can be used where hai lifts are required.

6. Monorail system:-

In tunnels and in dam sites, a single track is laid to carry a monorail power wagon which moves at a speed of 80 metre per minute.

This type of transportation can be used for covering long distances.

7. Concrete ducket and skip:-

The capacity of the skip varies from about 0.2 metre cube to 10 m cube.

       gkgautam6036.blogspot.com