Using images 1 and 2 above and in a bid to also demystify the raft foundation cost, this article will
deal extensively on how to calculate your concrete materials like cement, sand and granite
that you will use for the foundation.
Often time concrete are mostly mixed in 1:2:4 ratio, when you see such specificationit simply means one bag of cement to four headpans of sand and eight headpans of granite.
Notice that first number represent a bag of cement which is equivalent to two headpans, hence the sand is taken as four headpanss and the granite represented by 4 in the ratio is taken as eight headpans.
Going by this knowledge it is easy for us to do a very fast calculation at least to be close to what we might need on site.
To do this calculation, add the sum of ratio 1+2+4=7
Calculate the cubic volume of concrete for foundation.
Going by the previous article the total lenght of trench was taken as 65.6m Height of concrete beam is 1.1m or 1100m from image 2 And width is 0.225m or 225mm therefore total volume of concrete beams =65.6m x 1.1 x 0.225 =16.236
Now divide 16.236 by the sum of the ratio which is 7
Taking a constant, the volume of a bag of cement is 0.035m’3
Divide 2.31943 by 0.035=66 bags of cement to do all the concrete
beams , however don’t forget that cement and sand will also be used for the blinding before the concrete beams are placed .
For the sand reqd.,multiply 2.31943m3 by 2 to know the volume since it is in ratio of 1:2:4
Therefore volume of sand requires =4.63886m3
If we take volume of a tipper as 3.8m3 then 4.63886/3.8=1 1/2 trip of 5 tons tipper for the concrete beam.
For the granite use the same ratio of 1 bag of cement to 4 headpans of sand to 8 headpans of
So for granite reqd, multiply 2.31943m3 by 4 to
know the volume since it is in the ratio of 1:2:4 therefore volume of granite requires=9.27772
If we take volume of a tipper as 3.8m3 then,
9.27772/3.8=2 1/2 trips of granite (Disregarding water and and other attending expenses
*If one bag cost N1,800, then 66 bags =N118,800
*And if one trip of sand is N15,000 then 1 1/2 trips =N22,500
*And if one trip of 5 tons of granite=N30,000 then granite cost needed =2 1/2 x N30,000
Total=N118,800 + N22,500 + N75,000=N216,300
For the german floor or oversite concrete-
Multiply the lenght by breadth by the thickness or
width of the plan from image.
Add 3.825 +3.95 +1.375+1.25+4.975+1.25=16.625
So multiply the sum for the volume=16.625 x10.560 x 0.2=35.112m3
To know the number of cement required divide 35.112 by the sum of the ratio which is 7 =35.112 / 7
Taking a constant, the volume of a bag of cement which is 0.035m3,
divide 5.016m3 by 0.035 =143 bags of cement for the german floor or oversite concrete.
Apply the steps above for the sand and granite,
Multiply 5.016 by 2=10.032, now divide by 3.8m3 =3 trips of 5tons sharp sand
multiply 5.016 by 4=20.064, now divide by 3.8m3 =5 1/2 trips of 5 tons granite
So if one bag of cement cost N1800 then 143 bags of cement will cost N1800 x 143=N257,400
And if one trip of sand cost N15,000 then 3 trips of 5 tons sharp sand =N45,000
*And if one trip of 5 tons granite cost =N30,000
then 5 1/2 trips of 5 tons granite =N165,000
So total for concrete excluding other attendingmaterials
This is hard to understand I believe but you can still study it by bits.