Concrete Lessons: mix design

raw materials January 07, 2019

How to calculate Concrete Raw Materials Measurement box sizes at the site

For manual batching of concrete raw materials at a site in correct proportion, concrete raw material measuring boxes are used. This method of batching is generally used where a small quantity of concrete to be prepared using stacked raw materials. This is a volume batching and it should not be practised when weight batching is available to avoid less deviation.

General Requirments:

To calculate measuring box sizes we need to do the mix design and find out the quantity of cement, sand, and aggregate (both 20 and 10mm) to be used in one cubic meter of concrete. We also need to calculate the bulk density of raw materials (sand and aggregates) as well as bulking of sand at the site.

Calculations:

Let's assume for 1 cubic meter of concrete the required quantity of raw materials are-

Cement - 337.5 kg

Sand - 723 kg

Coarse aggregate - 1200 kg (65% 20mm and 35% 10mm)

Now let's assume these followings -

The bulk density of sand - 1445 kg/cm

The bulk density of coarse aggregate - 1408 kg/cm

Now let's calculate the required quantity of raw materials for 1 bag (50kg) of cement,

Note: Generally this type of batching is done with respect to 1 bag cement.

now 337.5 kg cement = 6.75 bags of cement

for 6.75 bags of cement, the sand quantity is 723 kg

for 1 bag of cement the quantity of sand is (723/6.75)= 107.11 kg

and coarse aggregate is (1200/6.75)= 177.78 kg

In which 20mm aggregate is (177.78x(

Now the volume of 107.11 kg sand = (107.11/1445)cum=0.07412 cum=

and volume of 177.78 kg aggregate=(177.78/1408)cum=0.12626 cum (20mm -0.082069 cum, 10mm-0.044191cum)

let's assume the length and breadth of the box is 300mm and 300mm and height x, and we need to mix 2 box of sand and aggregate (both 20 and 10mm) for 1 mix,

now for sand x is =0.07412/2*(0.3*0.3)= 0.411m = 411 mm
and for the coarse aggregate of 20mm size x is = 0.082069/2*(0.3*0.3)= 0.455m = 455mm
and for coarse aggregate of 10mm size is = 0.044191/2*(0.3*0.3)=0.245m = 245 mm

So the sizes of the measuring boxes and mix proportion for 1 bag of cement will be -
For Sand - 300mm x 300mm x 411mm (2 box)
For 20 mm CA - 300mm x 300mm x 455mm (2 box)
for 10 mm CA - 300mm x 300mm x 245mm (2box)