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Wednesday, May 23, 2018

How to Calculate a Plane Concrete Quantity




The formula for calculation of materials for required volume of concrete is given by:
quantities-of-mateirals-for-concrete-formula
Where, V.c 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.
The air content has been ignored in this calculation.
This method of calculation for quantities of materials for concrete takes into account the mix proportions from design mix or nominal mixes for structural strength and durability requirement.
Now we will learn the material calculation by an example.

Calculating Quantities of Materials for per cubic meter or cubic feet or cubic yards concrete

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 20mm. The water cement ratio required for mixing of concrete is taken as 0.45.
Assuming bulk densities of materials per cubic meter, cubic feet and cubic yards as follows:
Cement = 1500 kg/m= 93.642 lb/ft3 = 3.4682 lb/cubic yards
Sand = 1700 kg/m= 105 lb/ft3 = 3.89 lb/cubic yards
Coarse aggregates = 1650 kg/m= 105 lb/ft3 = 3.89 lb/cubic yards
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.
Therefore, the ratio of masses of these materials w.r.t. cement will as follows =
Ratio of masses of cement, sand and coarse aggregates
= 1 : 1.7 : 3.3
The water cement ratio = 0.45
Now we will calculate the volume of concrete that can be produced with one bag of cement (i.e. 50 kg cement) for the mass proportions of concrete materials.
Thus, the absolute volume of concrete for 50 kg of cement =
Volume of concrete for 1 bag of cement
Thus, for the proportion of mix considered, with one bag of cement of 50 kg, 0.1345 m3 of concrete can be produced.
We have considered an entrained air of 2%. Thus the actual volume of concrete for 1 cubic meter of compacted concrete construction will be = 1 -0.02 = 0.98 m3.
Thus, the quantity of cement required for 1 cubic meter of concrete = 0.98/0.1345 = 7.29 bags of cement.
The quantities of materials for 1 m3 of concrete production can be calculated as follows:
The weight of cement required = 7.29 x 50 = 364.5 kg.
Weight of fine aggregate (sand) = 1.5 x 364.5 = 546.75 kg.
Weight of coarse aggregate = 3 x 364.5 = 1093.5 kg.








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