WHAT IS VOLUME BATCHING OF CONCRETE AND HOW IT IS DONE IN FIELD?
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WHAT IS VOLUME BATCHING OF CONCRETE?
Batching of concrete means measuring different ingredients of concrete (i.e. cement, sand, coarse aggregate and water) before mixing it. When this measurement is done on the basis of volume, we call it Volume Batching. Below are mentioned some of important points to remember before adopting volume batching method in field.
- Volume batching is not a good method for measuring concrete materials.
- It is not applicable in case of reinforced concrete structure.
- This method of concrete batching may not be economical.
- It can be only used for unimportant concrete or for small concrete works.
HOW VOLUME BATCHING IS DONE IN FIELD?
Before batching concrete ingredients in terms of volume, we need to know two things.
- What is the relative proportion of concrete ingredients in terms of volume?
- What is the water-cement ratio?
After knowing these two things you can proceed to batch concrete ingredients in field.
The table shown below can be used as a reference to find out relative proportion of different ingredients, for different grades of concrete.
Grade of Concrete
Relative Proportion of Ingredients by Volume
In General We Specify It As
The water-cement ratio to be used must be as per the contract.
STEP-1-BATCHING OF CEMENT
Cement is always measured by weight. Mostly it is used in terms of bags. One bag of cement weighs 50 kg and has a volume of 35 litres (or, 0.035m3). Cement should not be batched by volume because its weight per unit volume varies according to the way the container is filled.
STEP-2-BATCHING OF AGGREGATE (BY VOLUME)
A gauge box is used (as shown in the picture) for batching of fine and coarse aggregate by volume. The box should not be too shallow. It should be completely filled with aggregates. The top of the materials should be struck off level with a straight edge. The ratio of materials of concrete decides the capacity of the box. Generally capacity of a gauge box is equal to the volume of one bag of cement (i.e. 35 litres). Convenient sizes of gauge boxes to suit different proportions are given in the table below.
Capacity In Litres
Inside Dimensions of gauge box in cm
Note: The moisture present in aggregates and bulking of sand must be accounted for while volume batching is adopted.
The following table gives the approximate surface moisture carried by aggregates as per IS-456-2000.
Condition of Aggregates
Approximate Quantity of Surface Mositure
Percent by Mass
Litre per m3
Very wet sand
Moderately wet sand
Moist gravel or crushed rock
STEP-3-BATCHING OF WATER
Water is measured either in kg or litres as may be convenient. In this case, the two units are same, as the density of water is one kg per litre. The quantity of water required is calculated by multiplying water-cement ratio with weight of cement.
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