COMPUTATION METHOD OF CONCRETE VOLUME CALCULATION
The computation method of concrete volume calculation involves the use of a formula which specifies each constituent element. The formula for calculating concrete volume and materials required is given as
Vc = W + C + Fa + Ca
1000 1000Sc 1000Sfa 1000Sca
Where 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
While Sc, Sfa, and Sca are the specific gravities of cement, fine aggregates, and coarse aggregates respectively. In this formula, the air content has been ignored
This method of calculating the concrete volume and quantities of materials takes into account the mix proportions from design mix or nominal mixes for structural strength and durability requirement.
Calculation of materials Quantities per cubic meter concrete
Let us consider concrete with a mix ratio of 1:1.5:3 with water cement ratio of 0.45
SOLUTION – COMPUTATION METHOD OF CONCRETE VOLUME
From the question above, 1 represents part of cement, 1.5 represent parts of fine aggregates and 3 parts of coarse aggregates of a maximum size of 20mm.
Since volume has a close relationship with density, let us outline the density of the constituent of the concrete.
Cement = 1440 kg/m3, Sand = 1600 kg/m3, Coarse aggregates = 1600 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 is assumed to be 2%.
DRY VOLUME OF MATERIALS EXPRESSED IN TERMS OF MASSES
Cement = 1 x 1440 = 1440
Sand = 1.5 x 1600 = 2400
Coarse aggregate = 3 x 1600 = 4950.
Therefore, the ratio of masses of these materials with respect to cement will be as follows
1440 : 2400 : 4950
1440 : 1440 : 1440
= 1: 1.7 : 3.4
The water cement ratio = 0.45
Now let us calculate the volume of concrete that can be produce with one bag of cement (i.e. 50 kg) using the formula.
The absolute volume of concrete that can be produce with 50 kg of cement is thus:
Vc = 0.45 x 50 + 1 x 50 + 1.7 x 50 + 3.4 x 50
1000 1000 x 3.15 1000 x 2.6 1000 x 2.6
Vc = 0.0225 + 0.0158 + 0.0326 + 0.0653= 0.136m3
Thus, for the proportion of mix considered, one bag of cement of 50 kg will produce a concrete of volume 0.1362m3
We have considered an entrained air of 2%. Therefore, the actual volume of concrete for 1 cubic meter of compacted concrete for construction will be = 1 -0.02 = 0.98m3.
Since the volume of concrete that be produce with one bag of cement is 0.1362m3, the quantity of cement required for 1 cubic meter of concrete will be = 0.98/0.1362 = 7.19 approximately, 7 bags of cement.
THE QUANTITIES OF MATERIALS FOR 1m3 OF CONCRETE – COMPUTATION METHOD OF CONCRETE VOLUME
The quantity of materials needed to produce 1m3 of concrete in term of weight can be calculated as follows:
The weight of cement required = 7.19 x 50 = 359.5 kg.
Weight of fine aggregate (sand) = 1.5 x 359.5 = 539.25 kg.
Weight of coarse aggregate = 3 x 359.5 = 1078.5 kg.