If you want to estimate concrete ingredients, you need to know the dry volume of concrete.
To estimate the concrete quantity we just take the dimension from drawings and then calculate the volume. The result we get is the actual concrete quantity and it is the wet volume of concrete.
If you order ready-mix concrete from suppliers then this estimation is correct and you don’t have to do anything.
What is The Dry Volume of Concrete
The prime ingredients of concrete are cement, fine aggregate (sand), and coarse aggregate (stone/brick chips). Concrete is produced by adding water with the mix of these ingredients.
The volume of the mix of concrete ingredients before adding water is the dry volume of concrete.
Difference Between “Wet Volume” and “Dry Volume” of Concrete
After adding water the volume of concrete ingredients is reduced to a certain level. It is happened due to the presence of air voids and pores in concrete ingredients.
Let me give you an example.
If you through a glass of water on a stack of sand, you’ll see a trench where the water is dropped. It’s happened due to evaporate air voids from sand. And thus, the volume is reduced.
How to Calculate The Dry Volume of Concrete
You can get wet volume by multiplying dimensions of a concrete member from drawing. When we need to get the dry volume of concrete, we just multiply the wet volume by 1.54.
Now the question is what is 1.54? How do we get that?
To understand this, we need to know the air voids and pores containing capability of concrete ingredients.
Air voids containing capability of,
- Coarse aggregate (stone/brick chips) – 32% to 34%
- Fine aggregate (sand) – 20% to 27%
Due to very fine particles, air voids capability of cement is ignored.
If we take the highest percentage of air voids in both coarse and fine aggregates, we get,
= 34% + 27%
But when sand and cement is mixed with coarse aggregate, it evaporates some air voids from the coarse aggregate. The percentage of this is 5% to 7%.
If we deduct this, we’ll get,
= 61% – 7%
That means the dry volume of concrete ingredients is reduced 54% after adding water. in other words, the wet volume of concrete is increased by 54% in the dry condition.
So, the formula of dry volume of concrete is,
= wet volume of concrete x 1.54.
Practical Example of Calculating The “Dry Volume of Concrete”
Suppose, you need to calculate the dry volume of concrete for an RCC column. The column dimension is given in the drawing as 30″ x 30″ and the height of the column is 10′.
So, the wet volume of concrete for the column is,
= 30″ x 30″ x 10′
= 62.50 cubic feet (30″ = 2½′)
The dry volume of concrete for the column is,
= wet volume x 1.54
= 62.50 x 1.54
= 96.25 cubic feet.
To get the dry volume of concrete, first, calculate the wet volume of concrete by multiplying the dimension of concrete members as shown in the drawing. Then multiply the result by 1.54. That’s it.
Get The “Estimating Cheat Sheet” Free.