TRANSPORTING, PLACING OF CONCRETE And COMPACTION OF CONCRETE
The two important precautions is necessary in concrete mixing
1) The concrete is transported in such a way that there no segregation of aggregate.
2) Under no circumstances the water should be added to concrete during its passage from mixer to the form work.
Types of transportation
1. Pans
2. Wheel barrows
3. Crane, Bucket and Rope way
4. Truck mixer and dumpers
5. Belt conveyors
6. Chute
7. Skip and hoist
8. Transit mixer
9. Pumps and Pipe lines
1) Pans: It is adopted in small works.
2) Wheel barrows: This is used for moderate distance.
3) Crane, Bucket and rope way: A Crane and bucket is used for transporting concrete above ground level. Rope way and bucket are used for transporting concrete to a place where simple method of transportation is not feasible. For the construction works in a valley or the construction work of a pier in the river or for dam construction, this method is adopted.
4) Truck mixer and Dumpers: For large concrete works particularly for concrete to be placed at ground level, trucks and dumpers are used.
5) Belt conveyors: This method is adopted when the construction site is 250m from place of mixing.
6) Chute: Chutes are generally provided for transporting concrete from ground level to lower
7) Skip and hoist: This is one of the widely adopted methods for transporting concrete vertically up for multistory building construction.At that point, the skip discharges the concrete automatically or manual Labour.
8) Transit mixer: This is used where concrete has to transported for long distances form the mixing plant ( Batching plant) to the place of construction. The capacity of transit mixer varies from 4 to 7cum.
9) Pumps and Pipe lines: Pumping concrete through steel pipelines is one Of the successful methods of transporting concrete. Pumped concrete has largely been used in construction of multistoried buildings, tunnels, and bridges. The concrete can be transported from batching plant to the place of construction with the help of pumps.
PLACING OF CONCRETE
The precautions to be taken during placing of concrete are as follows
1. The form work on the surface which is to come in contact with fresh concrete should be properly cleaned, prepared and well watered.
2. The large quantity of concrete should not deposited at a time.
3. The concrete should not be dropped at a vertical distance of 1m to prevent segregation.
4. Walking on the freshly prepared concrete should be avoided.
5. Concrete should be deposited in horizontal layers of about 15cm height for mass concrete layers may be of 40 cm to 50cm height.
6. The concrete should be placed on the form work as soon as possible.
7. During placing it should seen that all edges and comers of concrete surface remain unbroken, Slurp and straight in line.
8. It should be laid continuously to avoid formation of irregular lines and tracks.
9. Old surface should be made rough and clean before placing the new layer of concrete.
COMPACTION OF CONCRETE
The process of consolidation of concrete mix after placing in position is called compaction of concrete., the object of compaction is to remove air Bubles and to give maximum density to concrete to provide proper contact to ensure required bond between the reinforcement and •concrete to exhibit homogeneity.
1) Hand compaction
For unimportant works the compaction of concrete is carried out by hand method which includes Rodding , Tamping, Ramming.
2) Compaction by vibrator
Vibrators are mechanical devices which are used to compact concrete in the formwork. The advantages of vibrators over hand methods are as follows:
a. The quality of concrete can be improved by use of vibrators.
b. The use of vibrators results in reduction of compaction time.
c. With the help of vibrator it is possible to deposit concrete in small openings at places where it will be difficult by hand compaction.
d. Such a concrete can be easily compacted by using vibrators.
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