Moving Concrete from Mixer to the Form: 12 Methods | Concrete Technology

The following points highlight the twelve methods used for moving concrete from mixer to the form. The methods are: 1. Pan Method 2. Transportation by Wheel Barrows 3. Transportation Dumpers and Trucks 4. Transportation by Tipping Lorries 5. Transportation by Monorail and Jubilee Trucks 6. Transportation-by Belt Conveyer 7. Transport-by Hoist and a Few Others.

Method # 1. Pan Method:

This method of concrete transportation can be employed for small jobs where quantity of concrete required is small and labour is available at cheap rates in abundance.

This method can also be employed at site where other mode of transportation is not feasible along narrow lanes. In this method labourer carry concrete on their head in iron pans. The main disadvantage of this method is that the progress of work is slow. It is costly also.

Method # 2. Transportation by Wheel Barrows:

For small works, steel wheel barrows with pneumatic tyres can be used for moderate distances. The wheel barrows can be used on hard surface tracks. They, can also be used where track can be prepared by laying planks. The capacity of a wheel barrow varies from 70 litres to 80 litres. However hand cart with two wheels having larger capacity can also be used, but pulling such carts in loose soils is difficult. In more uneven level areas concrete transported by these barrows are liable to segregation.

(2-b) Power Barrows:

The power driven wheel barrows can be used upto 350 meter distances on unlevelled surface. With the help of these barrows about 30 batches per hour can be lifted from the mixer. However in sandy soils these barrows cannot be used.

Method # 3. Transportation by Dumpers and Trucks:

These are special types of trucks. These dumpers have been found suitable to transport concrete upto 350 metres without segregation and setting. The uses of dumpers have been found more suitable on loose and uneven grounds. The capacity of a dumper is 2 to 3 m³ while that of trucks is 4 m³.

Method # 4. Transportation by Tipping Lorries:

Tipping Lorries can be used to transport concrete upto 5 km. Concrete to be transported to a distance more than 350 m should contain lesser amount of water, because there is likelihood of segregation in the transition due to shaking and bad condition of the road etc. The effect of segregation can be minimised by keeping the thicker layer of concrete in the lorry. Usually the height or thickness of concrete in the lorry should not be less than 40 cms.

Tipping Lorries are generally used for transporting readymade concrete. These Lorries have arrangements for receiving, loading and discharging arrangements. With the help of these Lorries the mix is discharged directly into the struc­ture. These Lorries are used for the transport of concrete for the construction of roads, air fields and pave­ments, dams, tunnels and canal lining etc.

Method # 5. Transportation by Monorail and Jubilee Trucks:

Monorail trucks are very convenient for use with small and medium size mixing plants. Their main adv­antage is that they can be used across difficult and narrow sites without requiring much space. The rail is readily fixed and can be moved to new positions as the job proceeds. Their main disadvantage is that they need a special type of rail line, which is very costly. However they can be used in all types of terrain.

Jubilee Trucks are special type of trucks which can be used to transport concrete through soft and diffi­cult terrain without much difficulty.

Method # 6. Transportation-by Belt Conveyer:

Belt conveyers are available in convenient forms which allow the movement of concrete easily to diff­erent parts at the site. This method is used when concrete is required to be transported continuously. This method is most suitable for concreting in hot-climate at a distance of 250 m to 500 m from the mixing site. This method can also be used to carry concrete up slopes less than 30°. This method has proved very useful at places where other mode of transportation of concrete is not feasible.

Concrete to be transported by belt conveyer should not be very wet. The slump of the concrete should not be more than 9 cms in any case. However slump of 6 cms is quite sufficient.

The belt used has a rubber covering of 60 cms width. The speed of conveyer should not be more than 1 m per second. The line of conveys should not have any break in the plan. As stated above, the inclination of the conveyer should not be more than 30° in any case. However for different slumps, following incli­nations have been suggested as a guide.

Flat belts are used only upto 20 m distances. For larger distances trough shaped belts are used. While concrete is unloaded or transferred from one part of the conveyer to other.

Method # 7. Transport-by Hoist:

Now a days hoists are more frequently used to transport concrete at building sites upto a height of 150 m. The capacity of hoist usually adopted is 200 lit., 340 lit. or 510 lit. These hoist work at a speed of 75 meter per minute.

Method # 8. Transport-by Crane:

When cranes are used to transport concrete a suitable bucket or skip is required. One of the types of skip is known as Lay back skip. It is designed to fall on its back when lowered to the ground and it can be filled from a low level mixer discharge. When it is raised, it is pulled up right, and can discharge its contents through a gate at its lower end. For larger batches dump buckets arc used. Usually these buckets are cylin­drical. Usually the capacity of such skips is about 115 lit. While using crane, care should be taken that concrete is not thrown from an excessive height, so that form work may not be damaged.

Method # 9. Transportation of Concrete by Elevating Tower and Chutes:

This system of concrete transportation is suitable for large dams. In this system the concrete is filled at the head of deep chutes, by buckets in a central tower. From this point, concrete reaches at the required place through these chutes. The height of tower- should not be higher than 170 m and the capacity of buc­kets should not be more than 1.3 m³.

Concrete to be used by this method should be sufficiently fluid. The slump of concrete should be more than 5.0 cms. For less fluid concrete, vibrators may be used on chutes to move the concrete. This method of concrete transportation has proved very useful when the strength of the concrete is not very important.

Method # 10. Transportation from Chutes:

Usually chutes are employed for transporting concrete from ground level to a lower level. The chute section should be lined with metal sheet and the slope of full length should be same. It should be not flatter than 1 vertical and 2.5 horizontal. The lay out of the chute should be such that concrete will be able to slide without segregation as a compact mass.

Though this method is not good method for concrete transporting, yet it is adopted when the movement of labour cannot be allowed due to lack of space or due to fear of disturbance to the reinforcement etc.

Method # 11. Transport of Concrete by Overhead Cable Ways:

In this system, concrete is transported by buckets by stretching cables on poles situated on the banks of the valley. This system is useful for large dams only.

With the help of this system, other construction material and equipment also can be transported. The capacity of buckets may be upto 6 m³. The buckets arc open at the bottom with gates.

Method # 12. Transportation of Concrete by Pumps:

Transport of concrete by means of pumps has been found very useful in the following circumstances:

1. At congested sites where mixing plant cannot be taken close to the point of placing concrete.

2. At sites where storing of aggregate is not possible due to non-availability of space.

3. Concrete by this method can be delivered to points over a wide area otherwise not easily acces­sible.

4. This mode of transportation has been found very useful for tunnel lining, large mass concrete structures, densely reinforced concrete structures, etc.

5. This method is more economical where large quantities of concrete are required.

Pumped concrete is free from segregation. Pumping delivers the concrete direct from the mixer to the form and thus avoids the double handling. Placing can proceed at the rate of the output of the mixer and is not held back by the limitations of transporting and placing equipment etc.