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
· The gauge boxes are made with comparatively deeper with narrow surface
· Sometimes 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 to 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
· Batch mixer
· 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.
