What is the ratio of components in grade M20 concrete?
1 : 1.5 : 3
Understanding Concrete Grades and Mix Ratios
Concrete is classified into different grades based on its characteristic compressive strength. The grade is denoted by the letter 'M' followed by a number, where 'M' stands for 'Mix' and the number represents the characteristic compressive strength of a 150 mm cube after 28 days, expressed in N/mm².
For lower concrete grades (up to M20 or M25), standard nominal mix ratios are often used. These ratios specify the proportions of cement, sand (fine aggregate), and coarse aggregate by volume or weight.
The ratio is typically expressed as Cement : Sand : Coarse Aggregate.
Analyzing the M20 Concrete Mix Ratio
The question asks for the ratio of components in grade M20 concrete. M20 is a commonly used grade for various construction purposes.
According to standard nominal mix proportions, the ratio for M20 concrete is:
- Cement: 1 part
- Sand (Fine Aggregate): 1.5 parts
- Coarse Aggregate: 3 parts
This gives a ratio of 1 : 1.5 : 3.
This means that for every 1 part of cement, 1.5 parts of sand and 3 parts of coarse aggregate are used to make M20 concrete.
Common Concrete Nominal Mix Ratios
Here is a table showing the standard nominal mix ratios for some common concrete grades:
| Concrete Grade | Nominal Mix Ratio (Cement : Sand : Coarse Aggregate) | Characteristic Compressive Strength (N/mm²) |
|---|---|---|
| M5 | 1 : 5 : 10 | 5 |
| M7.5 | 1 : 4 : 8 | 7.5 |
| M10 | 1 : 3 : 6 | 10 |
| M15 | 1 : 2 : 4 | 15 |
| M20 | 1 : 1.5 : 3 | 20 |
| M25 | 1 : 1 : 2 | 25 |
For concrete grades higher than M20 or M25, nominal mixes are usually not recommended. Instead, 'design mix' concrete is preferred, where the proportions are scientifically determined based on specific material properties and desired concrete strength and workability.
Conclusion on M20 Concrete Ratio
Based on the standard nominal mix proportions, the ratio of cement, sand, and coarse aggregate for M20 concrete is 1 : 1.5 : 3.
Let's look at the given options:
- 1 : 3 : 6 (This ratio corresponds to M10 grade)
- 1 : 1.5 : 3 (This ratio corresponds to M20 grade)
- 1 : 1 : 2 (This ratio corresponds to M25 grade)
- 1 : 2 : 4 (This ratio corresponds to M15 grade)
Therefore, the correct ratio for M20 concrete is 1 : 1.5 : 3.
Revision Table: Concrete Mix Ratios
| Concrete Grade | Mix Ratio (C:S:A) | Strength (N/mm²) |
|---|---|---|
| M5 | 1:5:10 | 5 |
| M7.5 | 1:4:8 | 7.5 |
| M10 | 1:3:6 | 10 |
| M15 | 1:2:4 | 15 |
| M20 | 1:1.5:3 | 20 |
| M25 | 1:1:2 | 25 |
Additional Information: Understanding Concrete Grades
Concrete strength is crucial in construction. The characteristic compressive strength is defined as the strength below which not more than 5% of the test results are expected to fall. This is determined by testing standard concrete cubes (or cylinders) after a specified curing period, typically 28 days.
- Nominal Mix: These are prescribed proportions based on experience and provide a reasonable assurance of achieving the target strength for lower grades. They are simple to use but may not be the most economical or precise method.
- Design Mix: For higher strength requirements or large projects, concrete proportions are determined through laboratory tests using specific materials to meet specified strength and performance criteria. This method is more accurate and potentially more economical for large volumes.
- M20 concrete is widely used for slabs, beams, columns, and foundations in residential and commercial buildings.
Important Questions from Concrete
The separation of the constituent materials of concrete is known as:
Creep which is a strain due to loading with no loss of moisture?
The reduction in the strength of cores can be as high as ______ for 40 MPa concrete.
A good method of maintaining a satisfactory state of wetness in a body of concrete to promote continuous hydration when original water/cement ratio used is NOT less than 0.5 is known as:
Retarders are used for:
