Transportation of concrete is a method of moving fresh concrete from the mixing plant to the place where it needs to be deposed in the structural element. Since the time taken in the method of transportation of concrete mainly depends on the initial setting time and the need for workability at the site, it should be a design parameter.
For deciding appropriate admixtures in concrete to improve specific properties, the transportation of concrete method is pre-decided in advance.
Transportation of Concrete Methods
Following are the different transportation of concrete methods,
1. Mortar Pan
Mortar pan is a commonly used method in our country, especially for small-scale works, where the concrete is carried in small quantities. This method is more labor-intensive.
There are significantly fewer possibilities for concrete segregation, but this method exposes larger surface areas of concrete for dry conditions in thick members. This results in substantial water loss due to more concrete exposure to an environment in hot weather.
This method is mostly adopted for ground-level, below-ground-level, and above-ground-level construction work without more difficulties.
The mortar pan must be wet to start with, and it must be clean during the entire operation of concreting.
2. Crane, Bucket, And Ropeway
Crane and Bucket are mostly the correct transportation of concrete equipment, especially for above-ground level. Cranes give more preference to high-rise construction projects. Cranes are quick and versatile to move concrete horizontally and vertically along the boom and enable concrete placement at the exact point.
Those cranes carry buckets or skips containing concrete. Skips have a discharge door at the bottom, whereas buckets are tilted for emptying. Excessive free fall of concrete should be avoided to minimize the segregation defect in concrete..
3. Wheel Barrow or Hand Cart
It is generally used on the ground level (i.e., road construction and other similar structures. Segregation can occur if the transportation of concrete is done on rough roads over a long distance. However, this vibration problem can be minimized if pneumatic tires are used.
4. Belt Conveyor
It has limited application in the concrete construction sector due to chances of segregation on steep slopes, roller points, and changes in the direction of the belt. Segregation also takes place due to the vibration of a rubber belt. Modern belt conveyors can have adjustable reach, traveling diverter, and variable speed both forward and reverse.
Conveyors can quickly place a large volume of concrete where access is limited, and portable belt conveyors are used for short distances or lifts.
The end discharge arrangements must prevent segregation and remove all the mortar on the belt’s return. In adverse, It also involves over-exposure of concrete to the environment.
Concrete should be remixed at the end of delivery before placing the final position.
5. Truck Mixer And Dumper
For large-scale concrete works, mostly concrete to be placed at ground level, trucks, dumpers, or ordinary open steel-body tipping lorries can be used. It is a most improved and better method for long lead concreting. The concrete is covered with a tarpaulin if transported in open trucks.
If long-distance is involved, agitators should be used, which prevents segregation and stiffening, and it also helps the mixing process at a slow speed. For road construction using slip form paver, a large quantity of concrete must be supplied continuously.
6. Skip and Hoist
High-rise structures for transporting concrete vertically up are a widely used method.
Then concrete is fed into the skip, which travels vertically on rails like a lift. After discharge, it is better to turn over the concrete before avoiding segregation. Transportation of concrete is practically impossible with the mortar pan and ladder for more than 3 to 4 number floors; in that case, the skip and hoist method is adopted.
The mixer feeds the skip, and the skip travels up over the rail up to the level where concrete is needed, and at that point, the skip discharges the concrete automatically or manually.
The quality of concrete, i.e., freedom from segregation, will depend upon the extent of travel and rolling over the rails. If the concrete has traveled a considerable height, concrete on discharge must be required to be turned over before being placed finally.
It is usually used for concreting in deep locations. The workability should not be changed to suit the delivery by a chute. This method is extensively used in the field, though it is technically not a very good method.
The slope should not be lower than 1V:2.5H; otherwise, concrete will not slide down smoothly.
8. Transit Mixer
In the ready-mix concrete plant, the transit mixer is one of the most popular concrete transporting equipment types. They are truck-mounted transit mixers with 4 to 7 cubic meters.
There are two variations; they are as follows;
1) Mixed concrete is transported to the site by keeping it agitated at a speed varying between 2 to 6 revolutions per minute.
2) At the central batching plant, the concrete is batched, and in the truck mixer, mixing is done either in transit or immediately before discharging concrete at the site.
9. Pump and Pipe-Line Method
It is the most complicated method uniquely proper for limited space or when a large quantity of concrete can be poured except in cold joints. The pumping of concrete can be done @ the rate of 8 to 70 cubic meters per hour. (The horizontal distance is approximately 300 meters, and the vertical distance is about 90 meters)
Generally, the pipe diameter is 8 to 20 cm, and it is made of steel, plastic, or aluminum. The slump value should be a minimum of 40 to 100 mm or 0.90 to 0.95 compacting factor for pumped concrete.
The workability may be reduced by 25% because of compaction at the delivery point, and while designing the mix, this factor should be kept in mind.
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