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Thursday, January 31, 2019

How to calculate cement sand and aggregate quantity in concrete


·         Nominal mixed concrete may be used for concrete of grade M 20 or lower.
·         To calculate the individual quantity of cement, sand and aggregate and water in 1 cum of concrete we assuming the nominal mix design concrete of grade M20.

Ø  As per IS 456:2000 in M20 grade of concrete the proportion of Cement, Sand and Aggregate is,
Cement: Sand: Aggregate = 1:1.5:3

Ø  Adding all the volume to obtain the total volume i.e.
Cement+Sand+Aggregate = 1+1.5+3 = 5.5

Ø  I am assuming 1.54 as factor of safety.
(As we know that, voids are there in dry mix of concrete. Water is added in dry material to make it wet concrete and then placed in shuttering particles slides to readjust in pores and voids reducing the volume of it. In case of stone aggregate the void ratio compressibility is 32 to 33% where as that of sand is 20% and assuming that the cement particles being very fine get adjusted in compressed voids total volume of dry material (having 0.33+0.20 = 0.53) has nearly 52 to 54% more volume than when in wet state.
So the volume of dry material for concrete is achieved by multiplying wet concrete by 1.54. Based on same reason if we want to get volume of dry material for mortar wet volume should be multiplied by 1.20. However some engineers add 5% to 10% to multiplicative figure of 1.54 or 1.20 to account for wastage and poor workmanship.)
Ø  So for 1 m3 of M20 grade wet concrete, the total dry Volume of concrete required is 1.54 m3.

·         Calculation for Volume of Cement in 1cum of Concrete(M20):-
For 1m3 of Concrete = 403.2Kgs of Cement is required.         

No. of Cement Bags required for 1m3 of Concrete = 403.2/50 = 8.06 ~ 8 bags. (1 Bag of cement = 50 kg)
Hence, cement required for 1cum of concrete = 8 bags.
·         Calculation for Volume of Sand (Fine Aggregate) in 1cum of Concrete(M20):-
Sand usually consists of moisture content. It increases the volume of sand (bulking of sand).
For accurate calculation use dry sand or include the effect of bulking.
Hence, sand required for 1 cum of concrete = 672 kg.

·         Calculation for  Volume of  Coarse Aggregate in 1cum of Concrete (M20):-
Density of aggregate may go higher if void spaces decreases. As size of 5 mm aggregate has more density when compared with 20mm aggregate.
Hence, 20mm aggregate required for 1 cum of Concrete = 1310.4 Kg 

·         Calculation for  Water Requirement for 1 cum of Concrete( M20):-

For the preparation of concrete required qty of water, is added to the dry mix of concrete, depending upon the workability and climatic factors. Generally, we maintain 0.35 – 0.50 of water cement ratio. Always remember above value may change according to the moisture content present in sand and aggregate.

Cement required for 1 cum of M20 grade concrete = 403.20 kg
Assuming Water Cement Ratio = 0.50 (50% of cement)
Water required for 1cum of Concrete =    403.20 x 0.50
                                                                    =    201.60 kg
                                                                    =    201.60 ltr.

·         From the above calculation we get the quantities of material for M20 grade of concrete as follows –
Cement = 403.20 kg
Sand = 672 kg
Aggregate = 1310.40 kg
Water = 201.60 liter
·         Similarly we can also calculate the requirement of materials (Cement, Sand, Aggregate & Water) for concrete grade like – M5, M7.5, M10, M15 etc.

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