Nominal mixes method of concrete mix design
Nominal mixes
Nominal or prescribed mixes are generally adopted for small jobs where cost exercising quality control is not Justifiable.
Indicates the normal mix proportions for ordinary concrete recommended by Indian Standard Code 456-1978 for the compressive strength range for -- at 28 days. If the concrete is mixed with sufficient water to make it work then the mix may achieve the required strength.
Normally, the nominal mixes result in a wastage of materials, as only part of the potential strength of fine aggregate, coarse aggregate and amount of water required for 1 bag of cement (50kg) we worked out with reference to IS code. The proportion of fine aggregate to coarse aggregate is modified from upper (1:11/2) to lower limit (1:21/2) as the grading of fine aggregates becomes finer (zone A to C) and the maximum size to the coarse aggregate becomes larger (10 mm to 40 mm)
Nominal mixes
Nominal or prescribed mixes are generally adopted for small jobs where cost exercising quality control is not Justifiable.
Indicates the normal mix proportions for ordinary concrete recommended by Indian Standard Code 456-1978 for the compressive strength range for -- at 28 days. If the concrete is mixed with sufficient water to make it work then the mix may achieve the required strength.
Normally, the nominal mixes result in a wastage of materials, as only part of the potential strength of fine aggregate, coarse aggregate and amount of water required for 1 bag of cement (50kg) we worked out with reference to IS code. The proportion of fine aggregate to coarse aggregate is modified from upper (1:11/2) to lower limit (1:21/2) as the grading of fine aggregates becomes finer (zone A to C) and the maximum size to the coarse aggregate becomes larger (10 mm to 40 mm)
| MAXIMUM SIZE OF COARSE AGGREGATE |
FINE AGGREGATE ZONE | ||
|---|---|---|---|
| A | B | C | |
| 10 mm | 1:1 | 1:11/2 | 1:2 |
| 20 mm | 1:11/2 | 1:2 | 1:21/2 |
| 40 mm | 1:2 | 1:21/2 | 1:3 |
The quantity of water to be added is limited as per code. The amount of water to be added is modified as per the moisture content of aggregates. If aggregates contain surface water then the equivalent of water associated with the volume aggregate is deducted from the total quantity of water has to be increased to overcome difficulties in placing and compaction of the concrete. the cement content is increased to maintain the water-cement ratio.
For general guidelines, the proportions of cement, fine and coarse aggregate for various grades of concrete.
| Grade Of Concrete | Nominal Mix by Volume Cement : Fine Aggregate (sand) : Coarse Aggregate |
|---|---|
| M 10 | 1:3:6 |
| M 15 | 1:2:4 |
| M 20 | 1:11/2:3 |
| M 25 | 1:1:2 |
Certain traditional mixes were produced with fixed cement aggregate proportions and given workability. The strength varies due to variability ingredients. To avoid this, if the specification regreding minimum compress strength, grading of aggregate, aggregate shape, mix proportion are added then it leaves no scope for the production of the satisfactory mix at minimum cost.