There are various factors affecting the yield of concrete for a given ratio of concrete ingredients, such as:
- water-cement ratio
- total size
- Method of compaction etc.
Concrete yield simply means the actual quantity of concrete produced when a given proportion of concrete ingredients are mixed in a certain way.
Two methods exist to calculate the yield of concrete, viz.
- by thumb rule
- full amount of material
1. by thumb rule
A rule of thumb can be used to estimate the approximate yield of concrete from a given concrete mix, when batched by volume.
If the ratio of concrete is A:B:C that is, if a cement parts, b parts of sand and C Parts of the coarse aggregate are mixed by volume, resulting in a volume of concrete (2/3)*(a+b+c).
2. according to the full quantity of material
Concrete yield can be calculated more accurately by considering the absolute amounts of the various ingredients used in the concrete (cement, sand, coarse aggregate and water) along with the amount of air trapped in the concrete. When concrete is well compacted, the amount of trapped air is less than 1% and, therefore, can be neglected.
Let it happen woo, a, b And C be the absolute amounts of water, cement, fine aggregate and coarse aggregate, respectively.
If we assume that the final quantity of concrete produced will be 1 then it means,
w + a + b + c = 1
The value of absolute volume can be obtained by the relation:
Absolute volume = material weight / (apparent specific gravity * unit weight of water)
Estimate the yield of concrete per bag of cement for a concrete mix of the ratio (1:2:4).
by thumb rule
The volume of 50 kg of cement in a bag of cement is assumed to be 0.035 sq.3,
therefore a = 0.035 square meters3
Then the volume of sand becomes, b = 2*0.035 square meter3
and the volume of the coarse aggregate becomes, C = 4*0.035 square meter3
Then the yield of concrete of the ratio (1:2:4)
= (2/3)*(0.035 + 2*0.035 + 4*0.035)
= 0.163 square meters3
by absolute volume method
The following assumptions are made before computing the absolute amounts of the various components of concrete.
- Specific gravity of cement 3.15. is taken as
- The specific gravity of sand is 2.65 and the unit weight is 16 kN/m. is taken as3,
- The specific gravity of the coarse aggregate is taken to be 2.80 and the unit weight is 15 kN/m. is taken as3,
- Water cement ratio 0.6 . Is
- The unit weight of water is 10 kN/m. Is3
Calculate the volume of each component of concrete, using the formula for absolute volume
|Absolute amount of cement (a,||= 0.50/(3.15*10)
= 0.02 square meter3
|Absolute amount of sand (b,||= 2 * 0.035 * 16 / (2.65 * 10)
= 0.04 square meters3
|Absolute volume of coarse aggregate (C,||= 4*0.035*15/(2.80*10)
= 0.07 square meter3
|Absolute amount of water (woo,||= 0.60*0.50/(1*10)
= 0.03 square meters3
|Total quantity of concrete produced i.e.,
yield of concrete
= 0.16 square meters3
notes to remember
- If the material is already tested for specific gravity and unit weight, that value can be used to find more accurate results.
- The water cement ratio calculated in this example is taken as 0.6. If you are using another water cement ratio, replace 0.60 with that value when calculating the absolute amount of water.
- Never use 0.035 if each bag of cement doesn’t weigh 50kg.