What Is Mix Design of Concrete?
Concrete mix design involves a process of preparation in which a mix of ingredients creates the required strength and durability for the concrete structure. The ingredients to be tested: water, fine aggregate (sand), coarse aggregate, cement, chemicals, reinforcement, and soil.
Nominal Mix
Nominal mix specifies the fix proportion of the cement, sand and aggregates. Ingredients of concrete are mixed on the basis of volume. It is a site-level mixing of ingredients to prepare a concrete mix. Such What Is Concrete | 31 Plush Different Types of Concrete mix is generally used in small quantity or where the load is not high.
Nominal Mix Concrete
Nominal mixes offer simplicity and under normal circumstances, have a margin of strength above that specified. However, due to the variability of mix ingredients the nominal concrete for given workability varies widely in strength. Nominal mix ratios for concrete are 1:2:4 for M15, 1:1.5:3 for M20 etc.
Design Mix
Design mix is a process to prepare the concrete by testing all necessary properties (like properties of cement, fine aggregate and coarse aggregate) of concrete ingredients. Ingredients of concrete are mixed on the basis of weight. It is generally designed from ready Mix Concrete (RMC) plant.
Nominal Mix Ratio and Design Mix Ratio
|
Concrete Grade |
Design | Mix Ratio | Compressive Strength | |
| MPa (N/mm2) | psi | |||
| M5 | Nominal Mix | 1:5:10 | 5 MPa | 725 psi |
| M7.5 | Nominal Mix | 1:4:8 | 7.5 MPa | 1087 psi |
| M10 | Nominal Mix | 1:3:6 | 10 MPa | 1450 psi |
| M15 | Nominal Mix | 1:2:4 | 15 MPa | 2175 psi |
| M20 | Nominal Mix | 1:1.5:3 | 20 MPa | 2900 psi |
| M25 | Nominal Mix | 1:1:2 | 25 MPa | 3625 psi |
| M30 | Design Mix | NA | 30 MPa | 4350 psi |
| M35 | Design Mix | NA | 35 MPa | 5075 psi |
| M40 | Design Mix | NA | 40 MPa | 5800 psi |
| M45 | Design Mix | NA | 45 MPa | 6525 psi |
| M50 | Design Mix | NA | 50 MPa | 7250 psi |
| M55 | Design Mix | NA | 55 MPa | 7975 psi |
| M60 | Design Mix | NA | 60 MPa | 8700 psi |
| M65 | Design Mix | NA | 65 MPa | 9425 psi |
| M70 | Design Mix | NA | 70 MPa | 10150 psi |
Difference Between Nominal Mix and Design Mix
1. Nominal Mix and Design Mix: Mixing
Nominal Mix: The nominal mix is site-level mixing small concrete mixer can be used to mix the ingredients.
Design Mix: The design mix is designed from a ready mix concrete plant that is RMC plant.
2. Nominal Mix and Design Mix: Mix Design
Nominal Mix: There are many grades of nominal mix concrete like M-5, M-7.5, M-10, M-15, and M-20.
Design Mix: Design mix is a process to prepare the concrete by testing all necessary properties (like properties of cement, fine aggregate and coarse aggregate) of concrete ingredients.
3. Nominal Mix and Design Mix: Tests
Nominal Mix: For a nominal mix, no laboratory tests are conducted.
Design Mix: The design mix is based on laboratory trial-and-error experiment method.
4. Nominal Mix and Design Mix: Time
Nominal Mix: The nominal mix is easy to make at the construction site. It does not take more time to decide the proportion because proportions are already given in IS456:2000.
Design Mix: Whereas the design mix is very difficult and its process takes more than 30 days, time to find out the most suitable mix for the project for design mix IS-20262 shall be followed.
5. Nominal Mix and Design Mix: Skilled Persons
Nominal Mix: For a nominal mix, there is no need of skilled persons.
Design Mix: Whereas for design mix skilled person shall be required to prepare the mix design.
6. Nominal Mix and Design Mix: Basis
Nominal Mix: The nominal mix is based on past experience and has no scientific approach.
Design Mix: Whereas the design mix is more scientific than the nominal mix.
7. Nominal Mix and Design Mix: Strength
Nominal Mix: The nominal mix may or may not give exactly design strength unless all other factors like compaction, water-cement ratio curing of concrete are strictly followed.
Design Mix: Whereas design mix not only makes concrete of design strength but also makes it economical too.
8. Nominal Mix and Design Mix: Accuracy
Nominal Mix: In the case of nominal mix water-cement ratio is considered by the assumption so if we do not take care of it sometimes it leads to bleeding segregation and may make concrete of poor strength and durability.
Design Mix: Whereas in the case of design mix, there is no such problem slump and strength can be related that is for the strength. We can use different slump by changing the water-cement ratio with or without admixtures.
9. Nominal Mix and Design Mix: Use
Nominal Mix: The nominal mix is preferred for simpler relatively unimportant and small concrete works, in other words, the nominal mixes adopted for ordinary concrete work nominal mix may be used for concrete of M 20 grade or lower grade.
Design Mix: Whereas design mixed is used for more extensive and important concrete works design mix can be used for all the grades but it is generally used for M 25 and above grades.
FAQ: The Mix Design of Concrete
What is concrete mix design?
Concrete mix design is the process of selecting the appropriate proportions of ingredients (water, fine aggregate, coarse aggregate, cement, chemicals, reinforcement, and soil) to achieve the desired strength and durability for a concrete structure.
What is a nominal mix?
A nominal mix specifies fixed proportions of cement, sand, and aggregates, mixed based on volume. It is typically used for small projects or where the load is not high. Common nominal mix ratios include 1:2:4 for M15 and 1:1.5:3 for M20.
What is a design mix?
A design mix is a process where concrete is prepared by testing all necessary properties of its ingredients. The mixing is done based on weight and is generally designed at a ready-mix concrete (RMC) plant. This method ensures that the concrete meets specific strength and durability requirements.
What are the key differences between nominal mix and design mix?
- Mixing Process: Nominal mix is site-level mixing, while design mix is prepared at an RMC plant.
- Proportions: Nominal mix uses fixed ratios from past experience, whereas design mix uses scientifically determined proportions.
- Testing: Nominal mix does not require laboratory tests; design mix is based on lab trial-and-error experiments.
- Time and Skill: Nominal mix is quicker and simpler, needing less skill. Design mix is time-consuming and requires skilled personnel.
- Strength and Accuracy: Nominal mix strength can vary, while design mix ensures precise strength and economic use of materials.
What are the nominal mix ratios for different concrete grades?
- M5: 1:5:10 (5 MPa, 725 psi)
- M7.5: 1:4:8 (7.5 MPa, 1087 psi)
- M10: 1:3:6 (10 MPa, 1450 psi)
- M15: 1:2:4 (15 MPa, 2175 psi)
- M20: 1:1.5:3 (20 MPa, 2900 psi)
- M25: 1:1:2 (25 MPa, 3625 psi)
For which grades of concrete is the design mix generally used?
Design mix is typically used for concrete grades M25 and above, where higher strength and durability are required.
Why is the design mix considered more scientific than the nominal mix?
The design mix is based on laboratory tests and scientific methods to determine the best proportions of ingredients, ensuring consistent quality, strength, and cost-effectiveness. The nominal mix relies on past experience and fixed ratios, which can lead to variability in concrete strength.
Can the nominal mix give the exact design strength?
Nominal mix may or may not achieve the exact design strength, as it depends on factors like compaction, water-cement ratio, and curing. Design mix, however, ensures the concrete meets the desired strength and quality requirements.
What type of projects typically use nominal mix concrete?
Nominal mix concrete is preferred for simpler, smaller, and relatively unimportant concrete works, generally for grades M20 or lower.
What are the advantages of using a design mix?
Design mix ensures concrete of the specified strength, is more economical, reduces waste, and allows for adjustments in slump and strength by modifying the water-cement ratio and using admixtures.
