Concrete Mix Design Calculation for M20, M25, M30 Concrete with Procedure & Example

Concrete mix design is a scientific and systematic process to determine the correct proportions of cement, fine aggregate, coarse aggregate, water, and admixtures for a desired concrete grade.

In this article, we will guide you through the step-by-step procedure of mix design for M20, M25, and M30 grades of concrete with a practical example based on IS 10262:2019 and IS 456:2000.

What is Concrete Mix Design?

Concrete mix design is the process of selecting suitable ingredients of concrete and determining their relative proportions with the objective of producing concrete of required strength, durability, and workability as economically as possible.

Read More On: The Importance of Concrete Mix Design in Construction

Objectives of Concrete Mix Design

To achieve target mean strength.
To ensure workability for fresh concrete.
To maintain durability and resistance against environmental exposure.
To ensure optimum economy without compromising quality.

Types of Mix Design

Nominal Mix – Fixed proportion as per IS 456:2000 (for M5 to M20)
Design Mix – Based on laboratory tests and performance requirements (for M25 and above)

Mix Design Grades Covered

M20 – Nominal mix (1:1.5:3)
M25 – Design mix
M30 – Design mix

Let us now go through the detailed step-by-step procedure of mix design for M25 grade concrete as an example.

Step-by-Step Concrete Mix Design Procedure (As per IS 10262:2019)

1. Data Collection

Before beginning the mix design, we must collect the following data:

Grade of Concrete: M25
Type of Cement: OPC 43 grade
Maximum size of aggregate: 20 mm
Minimum cement content: 300 kg/m³ (as per IS 456)
Workability: 75 mm slump
Exposure condition: Moderate
Method of placement: Pumping
Water-cement ratio (w/c): 0.45 (max for durability)
Admixture: Superplasticizer conforming to IS 9103

2. Target Mean Strength Calculation

We calculate the target strength (f'ck) using the formula:

f'ck = fck + 1.65 × S

Where:

fck = characteristic compressive strength (25 MPa for M25)
S = standard deviation (assumed as 4 MPa for M25)

f'ck = 25 + 1.65 × 4 = 31.6 MPa

3. Water-Cement Ratio Selection

From Table 5 of IS 456:2000:

For moderate exposure: w/c = 0.45 (max)
Based on experience and trial: Adopt w/c = 0.45

4. Water Content Determination

From Table 4 of IS 10262:2019:

Water content for 20 mm aggregate = 186 kg/m³ for 50 mm slump
For 75 mm slump, increase by 3%:

Water = 186 + (3% of 186) = 191.6 kg/m³

5. Cement Content Calculation

Cement content = Water content / w/c = 191.6 / 0.45 = 425.77 kg/m³

Check for minimum: 425.77 > 300 (OK)
Check for maximum: 425.77 < 450 (OK)

Use: 426 kg/m³

6. Coarse and Fine Aggregate Proportioning

From Table 5 of IS 10262:2019:

Volume of coarse aggregate corresponding to 20 mm size and Zone II sand for w/c = 0.45 is 0.62

Then, volume of fine aggregate = 1 - 0.62 = 0.38

7. Mix Calculations – Volume Method

Assume 1 m³ of concrete

Volume of concrete = 1 m³

Volume of cement = 426/3.15 × 1/1000 = 0.135 m³
Volume of water = 191.6/1 × 1/1000 = 0.192 m³
Volume of admixture = 0.5% of cement = 2.13 kg → 2.13/1.145 = 0.0019 m³ (assume sp. gravity 1.145)
Total volume of ingredients = 0.135 + 0.192 + 0.0019 = 0.3289 m³
Volume of aggregates = 1 – 0.3289 = 0.6711 m³

Coarse Aggregate = 0.6711 × 0.62 × 2.65 × 1000 = 1101.8 kg/m³

Fine Aggregate = 0.6711 × 0.38 × 2.6 × 1000 = 662.8 kg/m³

Final Mix Proportion for M25 Grade Concrete

Cement = 426 kg/m³
Water = 191.6 kg/m³
Fine Aggregate = 662.8 kg/m³
Coarse Aggregate = 1101.8 kg/m³

Admixture = 2.13 kg/m³

Mix Ratio by weight ≈ 1 : 1.55 : 2.58 (Cement : FA : CA)

Mix Proportion for M20 and M30

M20 Grade Concrete (Nominal Mix)

Ratio = 1 : 1.5 : 3
Cement = 383 kg/m³
Water = 191.5 kg/m³
FA = 575 kg/m³
CA = 1150 kg/m³
Slump = 75-100 mm

M30 Grade Concrete (Design Mix)

Cement = 450 kg/m³
Water = 180 kg/m³
FA = 600 kg/m³
CA = 1150 kg/m³
w/c = 0.4
Admixture = As per the requirement for slump

Also Read On: Factors Affecting The Choice of Mix Proportions

Important Notes for Site Application

Always conduct trial mixes and adjust based on actual site conditions.
Measure materials accurately to ensure consistency.
Ensure proper mixing, placing, and curing for desired strength.
Consider temperature, moisture, and curing methods as they influence final results.

Advantages of Design Mix Over Nominal Mix

Optimized cement content and cost savings
Better durability and performance
Enhanced workability and ease of placement
Targeted strength achievement

Common Mistakes to Avoid

Using fixed water-cement ratio for all conditions
Ignoring moisture correction in aggregates
Improper mixing leading to segregation
Not accounting for admixture effects

Conclusion

A well-designed concrete mix is the foundation of a successful structure. For M20, M25, and M30 grades, understanding the step-by-step process ensures quality, economy, and structural integrity. Always perform trial mixes and maintain quality control on site.

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