How to Calculate Quantity of Cement, Sand & Aggregates for Slab

Area of flat slab = 1000sq.ft = 93sq.m.

The minimum thickness provided for slab is 150mm. (As per IS 456)

150mm = 0.15 metres

Hence Wet volume = Area of slab x Thickness of slab

Wet volume = 93 x 0.15 = 13.95cu.m.

To calculate the quantities of materials we need dry volume

Dry volume = Wet volume x 1.54

[Volume of concrete cube = length x Width x Height = 1 x 1 x 1 = 1m³ (Wet volume)

When we convert this we volume into dry volume, the volume is increased by 54% of wet volume.

∴ Dry volume = Wet volume + 54% of Wet volume

= 1 + (54/100) x 1 =1 + 0.54 = 1.54]

∴ Dry volume = 13.95 x 1.54 = 21.48cu.m (approximately).

Generally, M20 grade concrete is predominantly used for construction purposes.

M20 = 1: 1.5: 3 (Cement:Sand:Aggregates) = (a:b:c)

Quantity of Cement:

Quantity of cement = Dry volume x (a/{a+b+c})

Quantity of cement = Dry volume x (1/{1+1.5+3}) for M20 grade concrete.

= 21.48 x (1/5.5}) = 3.90cu.m = 3.90cu.m

We need the quantity of cement in terms of bags.

Unit weight or Density of cement = 1440kg/cu.m.

Quantity of cement in kg(s) = 1440 x 3.90 = 5616kg

We know that 1 cement bag = 50kgs

∴ No. of cement bags required = 5616/50 = 112.32 bags =112 bags.

Quantity of Sand:

Quantity of sand = Dry volume x (b/{a+b+c})

∴ Quantity of sand = Dry volume x (1.5/{1+1.5+3}) for M20 grade concrete.

= 21.48 x (1.5/5.5}) = 5.85cu.m

Quantity of Aggregates:

Quantity of aggregates = Dry volume x (c/{a+b+c})

∴ Quantity of aggregates = Dry volume x (3/{1+1.5+3}) for M20 grade concrete.

= 21.48 x (3/5.5}) = 11.71cu.m

Result:

Cement = 112 bags.

Sand = 5.85cu.m

Aggregates = 11.71cu.m

 

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