Transportation of concrete is an important activity in the production of concrete. The time taken in transit should be a design parameter as it depends on the initial setting time as well as the requirement of workability at the destination. The method of transportation adopted at site should be decided in advance so that suitable admixtures can be decided. The various prevalent methods of transportation are as given below.
1. MORTAR PAN
It is a labour intensive method and generally used for small works. There are no chances of segregation of concrete. In hot weather, there is a substantial loss of water due to more exposure of concrete to environment.
2. WHEEL BARROW OR HAND CART
It is normally used on ground level i.e. road construction and other similar structures. Segregation can occur if transportation is done on rough roads, however this problem can be minimizes if pneumatic tyres are used.
3. BUCKET AND ROPEWAY
It is suitable for works in valley, over high piers and long dam sites. Excessive free fall of concrete should be avoided to minimize segregation.
4. TRUCK MIXER AND DUMPER
It is an improved and better method for long lead concreting. The concrete is covered with tarpaulin if it is transported in open trucks. If long distance is involved, agitators should be used.
5. BELT CONVEYOR
It has limited application due to chances of segregation on steep slopes, roller points and changes in direction of belt. It also involves over-exposure of concrete to environment.
It is generally used for concreting in deep locations. Care should be taken that slope should not be flatter than 1V:2.5H, otherwise concrete will not slide down. But workability should not be changed to suit the delivery by chute. Technically it is not a very good method but it is extensively used in the field.
7. SKIP AND HOIST
It is a widely used method for high rise structures. Concrete is fed into the skip which travels vertically on rails like a lift. After discharging, it is better to turn over the concrete before use to avoid segregation.
8. PUMP AND PIPE-LINE METHOD
It is the most sophisticated method particularly suitable for limited space or when a large quantity of concrete is to be poured without cold joints. Pumping of concrete can be done @ 8 to 70 cubic meters per hour up to a horizontal distance of 300 meter and vertical distance of 90 meter. Pipe dia is generally 8 to 20 cm and it is made of steel., plastic or aluminum. The workability for pumped concrete should have a minimum of 40 to 100 mm of slump or 0.90 to 0.95 compacting factor. At delivery point the workability may be reduced by 25% due to compaction and this factor should be kept in mind while designing the mix.
9. TRANSIT MIXER
Transit mixer is one of the most popular equipment for transporting concrete over a long distance particularly in ready mix concrete plant. They are truck mounted having a capacity of 4 to 7 cubic meter. There are two variations. In one, mixed concrete is transported to the site by keeping it agitated all along at a speed varying between 2 to 6 revolutions per minute. In other category, the concrete is batched at the central batching plant and mixing is done in the truck mixer either in transit or immediately prior to discharging concrete at site.