Which code mention nominal mix design, and why dry volume 1.52 to 1.54 cum assume? please explain
Nominal mix design IS CODE
- Thread starter ashok
- Start date
Dnyan Deshmukh
Staff member
First of all avoid using nominal mixes for doing concreting, in unavoidable situations and for small quantity of concrete you may use it.
Its always better to use design mixes by doing concrete mix design, its easier to do and not a difficult task, you can learn on how to do concrete mix design by clicking on below link.
Concrete Mix Design: Become Concrete Master
The Nominal Mix proportions are given in IS 456, Table No 09.
It specifies that nominal mixes may be used for concrete M20 or lower grades.
It also specifies that, you need to increase the cement content in mix by proportionately when you add extra water to achieve the workability.
Here The total quantity of dry aggregates includes fine and coarse aggregates.
I will not go in deep on how to adjust the combine grading, in Table 9 notes, for an average grading of fine aggregates (i.e.- of Zone - II, Table 4 of IS 383), the proportion shall be 1:1.5, 1:2 and 1:2.5 for maximum size of aggregates 10mm, 20mm and 40mm respectively.
This is what written in IS code for nominal concrete mixes, they to prefer a weight batching of concrete for more accurate results.
As per the site conditions, when weight batching of concrete is not possible, volume batching of concrete can be done.
First you need to find the proportion of FA (fine aggregates) and CA (coarse aggregates), for this you need to be sure of what maximum size of aggregate you gonna use in concrete, in most of the cases its 20mm. as i said i am not going deep in gradation, we will take default value specified in IS code.
So for 20mm aggregates as maximum size you FA:CA proportion will be 1:2
why dry volume 1.52 to 1.54 cum assume?
this has nothing to do with designing of concrete and its mostly related to reconciliation matter.
Now understand following;
When rock is in its natural condition and measured as 1 cum.
How much it will get measured if you crush it in small pieces - it will always measured in volume by more than a cum.
because it contains voids in it, so the volume is higher. in concrete once all ingredient added and mixed up correctly - they fill voids of each other and forms a solid mass.
So this is a reason why dry volume of concrete ingredients is more. (i gave a very basic and easily understandable reasoning in above lines, a non technical guy like home buyer can also understand this fact).
Hope you got answers to your questions.
You can also refer IS 10262 for learning concrete mix designing.
Its always better to use design mixes by doing concrete mix design, its easier to do and not a difficult task, you can learn on how to do concrete mix design by clicking on below link.
Concrete Mix Design: Become Concrete Master
The Nominal Mix proportions are given in IS 456, Table No 09.
It specifies that nominal mixes may be used for concrete M20 or lower grades.
It also specifies that, you need to increase the cement content in mix by proportionately when you add extra water to achieve the workability.
| Grade of Concrete | Total Quantity of Dry aggregate per 50Kg cement | Max water per 50Kg of cement |
|---|---|---|
M5 | 800 Kg | 60 Lit |
M7.5 | 625 Kg | 45 Lit |
M10 | 480 Kg | 34 Lit |
M15 | 330 Kg | 32 Lit |
M20 | 250 Kg | 30 Lit |
Here The total quantity of dry aggregates includes fine and coarse aggregates.
I will not go in deep on how to adjust the combine grading, in Table 9 notes, for an average grading of fine aggregates (i.e.- of Zone - II, Table 4 of IS 383), the proportion shall be 1:1.5, 1:2 and 1:2.5 for maximum size of aggregates 10mm, 20mm and 40mm respectively.
This is what written in IS code for nominal concrete mixes, they to prefer a weight batching of concrete for more accurate results.
As per the site conditions, when weight batching of concrete is not possible, volume batching of concrete can be done.
First you need to find the proportion of FA (fine aggregates) and CA (coarse aggregates), for this you need to be sure of what maximum size of aggregate you gonna use in concrete, in most of the cases its 20mm. as i said i am not going deep in gradation, we will take default value specified in IS code.
So for 20mm aggregates as maximum size you FA:CA proportion will be 1:2
why dry volume 1.52 to 1.54 cum assume?
this has nothing to do with designing of concrete and its mostly related to reconciliation matter.
Now understand following;
When rock is in its natural condition and measured as 1 cum.
How much it will get measured if you crush it in small pieces - it will always measured in volume by more than a cum.
because it contains voids in it, so the volume is higher. in concrete once all ingredient added and mixed up correctly - they fill voids of each other and forms a solid mass.
So this is a reason why dry volume of concrete ingredients is more. (i gave a very basic and easily understandable reasoning in above lines, a non technical guy like home buyer can also understand this fact).
Hope you got answers to your questions.
You can also refer IS 10262 for learning concrete mix designing.
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