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Chapter: Civil - Construction Techniques, Equipment And Practices - Concrete Technology

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Manufacturing of concrete

Production of concrete requires meticulous care at every stage The ingredients of good and bad concrete are same but good rules are not Observed it may become bad


Manufacturing of concrete

 

Introduction

Production of concrete requires meticulous care at every stage The ingredients of good and bad concrete are same but good rules are not Observed it may become bad

 

Manufacturing of concrete includes the following stages

1.

Batching

2.

Mixing

3.

Transporting

4.

Placing

5.

Compacting

6.

Curing

7.

Finishing

 

Batching

 

The measurement of materials for making concrete is known as batching. Methods of batching

 

 Volume

 batching

   Weigh batching

 

 

Volume batching

 

The required ingredients of conc. Are measured by volume basis

 

Volume batching is done by various types of gauge boxes

 

o The gauge boxes are made with comparatively deeper with narrow surface o Some times bottomless gauge boxes are used but it should be avoided

 

Volume batching is not a good practice because of the difficulties it offers to

granular material.

 

Some of the sand in loose condition weighs much less than the same volume of

dry compacted soil.

 

For un important concrete or any small job concrete may be batched by volume.

 

 

Weigh batching

 

It is the correct method of measuring materials for concrete.

 

 

Use of weight system in batching ,facilitates accuracy flexibility and simplicity

 

The different types of weigh batching are there, they are used based on the different

 

situation. In small works the weighing arrangement consist of two weighing buckets

 

connected to the

levers of spring loaded dials which indicates the load,

 

The weighing buckets are mounted on a central spindle about which they rotate

 

On large works the weigh bucket type of weighing equipment used ,the materials are fed from the over head storage hopper and it discharges by gravity.

 

 

Mixing

 

Thorough mixing of materials is essential for the production of uniform concrete

 

The mixing should ensure that the mass becomes homogeneous uniform in color and consistency.

 

        Types of mixing

Hand mixing

 

Machine mixing

 

Hand mixing

 

It is practiced for small scale un important concrete works. Hand mixing should be done over a impervious concrete or brick floor sufficiently large size take one bag of cement. Spread out and measure d out fine aggregates and course aggregate in alternative layers.

 

Pour the cement on the top of it and mix them dry by showel, turning the mixture over and over again until the uniformity of color is achieved. The uniform mixture is spread out in the thickness of about 20 cm. The water is taken and sprinkled over the mixture and simultaneously turned over. The operation is continued till such time a good uniform homogeneous concrete is obtained

 

 

Machine mixing

 

Mixing of concrete almost invariably carried ot by machine ,for reinforced concrete work medium or large scale concrete works .

 

Machine mixing is not only efficient it is also economical when quantity of concrete to be produced is large

 

Type of mixer for mixing concrete

 

1.     Batch mixer

 

2.     Continuous mixer

 

Concrete mixers are generally designed to run at a speed of 15 to 20 revolutions per minute

 

For proper mixing it is seen that about 25to 30 revolutions are required in a well designed mixer

 

It is important that a mixer should not stop in between concreting operations for this requirement concrete mixer must be kept maintained


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