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Thursday, May 14, 2015

CALCULATING THE REQUIRED QUANTITIES OF MATERIAL FOR CONCRETE


 
Quantity of material required for the production of required quantity of concrete of given mix proportions can be calculated by absolute volume method. 
Volume method is based on the principle that the volume of fully compacted concrete is equal to the absolute volume of all the materials of concrete, that is cement, fine aggregate (sand) , coarse aggregates and water.
SOURCE

Formula to calculate the desired quantity of materials is:
 
Vc: Absolute volume of fully compacted fresh concrete
W: Mass of water
C: Mass of cement
Fa: Mass of fine aggregates
Ca: Mass of coarse aggregates
Sc, Sfa and Sca are the specific gravities of cement, fine aggregates and coarse aggregates respectively.
*AIR CONTENT IS IGNORED IN CALCULATION
This method of calculation for quantity of material for concrete takes into account the mix proportions from design mix or nominal mixes for structural strength and durability requirement.

FOR EXAMPLE:
Consider concrete with mix proportion of 1:1.5:3 where, 1 is part of cement, 1.5 is part of fine aggregates and 3 is part of coarse aggregates of maximum size of 20 mm. The water cement ratio required for mixing of concrete is taken as 0.40
Assuming bulk densities of materials as follows:
Cement = 1500 kg/m3
Sand = 1700 kg/m3
Coarse aggregates = 1650 kg/m3
Specific gravities of concrete materials are as follows:
Cement = 3.15
Sand = 2.6
Coarse aggregates = 2.6.
The percentage of entrained air assumed is 2%.

The mix proportion of 1:1.5:3 by dry volume of materials can be expressed in terms of masses as:

Cement = 1 x 1500 = 1500
Sand = 1.5 x 1700 = 2550
Coarse aggregate = 3 x 1650 = 4950.
RATIO OF MASSES WITH RESPECT TO CEMENT:
Water cement ratio= 0.40
ABSOLUTE VOLUME OF CONCRETE FOR 50 KG (1  BAG) OF CEMENT:
CALCULATING THE REQUIRED QUANTITIES OF MATERIAL FOR CONCRETE
THEREFORE FROM ONE BAG OF CEMENT (50 KG) 0.13202 m3 OF CONCRETE CAN BE MADE.


FOR 1m3 OF CONCRETE 2% AIR IS ENTRAINED.
ACTUAL VOLUME OF CONCRETE= 1-0.02= 0.98m3


QUANTITY OF CEMENT REQUIRED FOR 1m3 OF CONCRETE= 0.98/0.13202=7.42 BAGS OF CEMENT
=7.42* 50 Kg
=371 Kg

Weight of fine aggregate (sand)= 1.5* 371=556.5 Kg
Weight of coarse aggregate =3* 371=1113 Kg

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