by This page presents an illustrative M55 concrete mix design using OPC 53 cement, 20 mm and 12.5 mm crushed coarse aggregates, crushed stone sand and a polycarboxylate-ether-based superplasticizer.
The calculations follow the general proportioning approach of IS 10262:2019. The final mix must be confirmed through laboratory and site trials using the actual cement, aggregates, water, admixture, batching system, placing method and project requirements.
Important: This is an initial trial mix, not a universal M55 concrete recipe. Final production quantities must be approved after trial-mix testing.
Page Contents
1. Mix Stipulations
| Property | Adopted value |
|---|---|
| Grade of concrete | M55 |
| Characteristic compressive strength at 28 days | 55 MPa |
| Cement | OPC 53 grade conforming to IS 269:2015 |
| Maximum nominal size of aggregate | 20 mm |
| Minimum cement content | 380 kg/m³, as adopted for the project |
| Maximum cement content | 450 kg/m³, as adopted for the project |
| Maximum water-cementitious ratio | 0.40 |
| Target slump | 125 ± 25 mm |
| Exposure condition | Moderate exposure for reinforced concrete |
| Concrete placement | Pumping is the governing assumption |
| Degree of supervision | Good |
| Coarse aggregate | Crushed angular aggregate |
| Fine aggregate | Crushed stone sand |
| Chemical admixture | Fosroc Auramix 400 |
| Admixture standard | IS 9103:1999 or the applicable project-specified edition |
| Design basis | Aggregates considered at saturated surface-dry condition |
Important exposure note
The maximum water-cementitious ratio of 0.40 and minimum cement content of 380 kg/m³ are treated as project-specific requirements in this example. They should be checked against the latest applicable IS 456 requirements, project specifications and governing authority specifications.
2. Material Properties
2.1 Cement and admixture
| Material | Property | Value |
|---|---|---|
| Cement | Type | OPC 53 grade |
| Cement | Specific gravity | 3.15 |
| Admixture | Product | Fosroc Auramix 400 |
| Admixture | Specific gravity | 1.09 |
| Admixture dosage used in calculation | Percentage by mass of cement | 0.60% |
2.2 Aggregate specific gravity
| Aggregate | Specific gravity |
|---|---|
| 20 mm coarse aggregate | 2.69 |
| 12.5 mm coarse aggregate | 2.69 |
| Crushed stone sand | 2.60 |
| Water | 1.00 |
The coarse aggregate blend is:
- 20 mm aggregate: 50%
- 12.5 mm aggregate: 50%
2.3 Aggregate absorption and moisture
| Aggregate | Water absorption | Free surface moisture |
|---|---|---|
| 20 mm coarse aggregate | 0.37% | Nil |
| 12.5 mm coarse aggregate | 0.54% | Nil |
| Crushed stone sand | 2.35% | Nil |
The mix calculations below are based on saturated surface-dry aggregate conditions. Actual field moisture correction is required before batching.
3. Sieve Analysis
3.1 Coarse aggregate grading
The combined coarse aggregate consists of 50% 20 mm aggregate and 50% 12.5 mm aggregate.
| IS sieve size | 20 mm aggregate passing (%) | 12.5 mm aggregate passing (%) | Combined passing (%) |
|---|---|---|---|
| 40 mm | 100.00 | 100.00 | 100.00 |
| 20 mm | 95.01 | 100.00 | 97.51 |
| 12.5 mm | 0.00 | 99.15 | 49.58 |
| 10 mm | 2.54 | 51.07 | 26.81 |
| 4.75 mm | 0.88 | 0.42 | 0.65 |
| Pan | 0.00 | 0.00 | 0.00 |
The combined passing percentage is calculated as:
Combined passing = 0.50 × passing of 20 mm aggregate + 0.50 × passing of 12.5 mm aggregate
The grading should be checked against the applicable coarse-aggregate grading requirements of IS 383:2016. The grading tables should not be incorrectly identified as “IS 383 Table 2.”
3.2 Fine aggregate grading
The crushed stone sand conforms approximately to grading Zone II.
| IS sieve size | Crushed stone sand passing (%) | Zone II range (%) |
|---|---|---|
| 4.75 mm | 100.00 | 90–100 |
| 2.36 mm | 85.88 | 75–100 |
| 1.18 mm | 58.95 | 55–90 |
| 600 micron | 38.87 | 35–59 |
| 300 micron | 21.47 | 8–30 |
| 150 micron | 9.74 | 0–10 |
The fine aggregate grading, percentage of fines and manufactured-sand requirements must be checked using the applicable provisions of IS 383:2016 and the project specification.
3.3 All-in aggregate grading
The approximate combined aggregate proportions used for the grading check are:
- 20 mm aggregate: 29.5%
- 12.5 mm aggregate: 29.5%
- Crushed stone sand: 41.0%
| Sieve size | 20 mm contribution (%) | 12.5 mm contribution (%) | Sand contribution (%) | Combined passing (%) |
|---|---|---|---|---|
| 40 mm | 100.00 | 100.00 | 100.00 | 100.00 |
| 20 mm | 95.01 | 100.00 | 100.00 | 98.53 |
| 4.75 mm | 0.88 | 0.42 | 100.00 | 41.38 |
| 600 micron | 0.00 | 0.00 | 38.87 | 15.94 |
| 150 micron | 0.00 | 0.00 | 9.74 | 3.99 |
The above aggregate blend is a proportioning check. Final grading must be verified using actual material test results.
4. Target Mean Strength
The characteristic compressive strength of M55 concrete is:
fck = 55 MPa
As per the IS 10262:2019 approach, the target mean strength is calculated as the higher of:
- fck + 1.65S
- fck + X
Where:
- fck = characteristic compressive strength
- S = standard deviation
- X = grade-dependent constant specified by the applicable standard
For example, if S is taken as 5 MPa and X is taken as 6.5 MPa:
fck + 1.65S = 55 + 1.65 × 5
= 63.25 MPa
fck + X = 55 + 6.5
= 61.50 MPa
Therefore, the code-based target in this illustration would be:
Target mean strength = 63.25 MPa
Project or MoRTH-specific target
If the governing project or MoRTH specification specifically requires a 14 MPa margin for M55 concrete:
Target mean strength = 55 + 14
= 69 MPa
The value of 69 MPa must not be presented as a universal target for every M55 design. It should be retained only when required by the governing project specification.
5. Selection of Water-Cement Ratio
The maximum water-cementitious ratio adopted for this example is:
Maximum w/cm = 0.40
Since no mineral admixture such as fly ash or GGBS is included:
Water-cementitious ratio = Water-cement ratio
The selected design water-cementitious ratio is:
Adopted w/cm = 0.34
This satisfies the adopted maximum requirement:
0.34 ≤ 0.40
6. Water Content Calculation
For 20 mm nominal maximum-size aggregate and 50 mm slump, the reference water content is taken as:
Water content = 186 litres/m³
The required slump is 125 mm. The increase over the reference slump is:
125 − 50 = 75 mm
For every 25 mm increase in slump, the water content is increased by approximately 3%.
Water increase:
75/25 × 3% = 9%
Adjusted water content:
186 × 1.09 = 202.74 litres/m³
Based on the laboratory trial performance of the superplasticizer, a 26% water reduction is considered:
Reduced water content:
202.74 × 0.74 = 150.03 litres/m³
Adopted free water content:
Water = 150 litres/m³
The 26% reduction is trial-specific. It must be confirmed using the actual cement, aggregate, admixture dosage, temperature, slump and slump-retention requirements.
7. Cementitious Content Calculation
Using the selected water-cementitious ratio:
Cementitious content = Water / w/cm
Cementitious content:
= 150 / 0.34
= 441.18 kg/m³
Adopted cement content:
Cement = 445 kg/m³
The adopted cement content satisfies the stated project limits:
380 kg/m³ ≤ 445 kg/m³ ≤ 450 kg/m³
Because no supplementary cementitious material is used in this example:
Cementitious material = OPC cement only
Actual water-cement ratio
Using the adopted cement content:
Actual w/c = 150 / 445
= 0.337
≈ 0.34
8. Chemical Admixture Content
The superplasticizer dosage is taken as 0.60% by mass of cement.
Admixture quantity:
= 445 × 0.60 / 100
= 2.67 kg/m³
The final dosage must be checked against the manufacturer’s recommended dosage range, cement compatibility, slump retention, setting time and trial results.
9. Coarse and Fine Aggregate Proportioning
For Zone II fine aggregate and 20 mm nominal maximum-size aggregate, the reference volume of coarse aggregate per unit volume of total aggregate at a water-cement ratio of 0.50 is taken as:
Volume of coarse aggregate = 0.62
The selected water-cementitious ratio is 0.34.
Decrease in water-cement ratio:
0.50 − 0.34 = 0.16
Adjustment:
(0.16 / 0.05) × 0.01 = 0.032
Corrected coarse aggregate volume:
0.62 + 0.032 = 0.652
For pumpability, a 10% reduction is adopted:
0.652 × 0.90 = 0.5868
Adopted coarse aggregate volume:
Coarse aggregate fraction = 0.59
Fine aggregate fraction:
Fine aggregate fraction = 1 − 0.59
= 0.41
The 10% pumpability adjustment is an initial design assumption. It must be confirmed through an actual pump trial. Bucket placement may require a separate trial and should not automatically use the same proportion.
10. Absolute Volume Calculation
The absolute-volume method is used for one cubic metre of concrete.
10.1 Cement volume
Volume of cement:
= Mass / (Specific gravity × 1000)
= 445 / (3.15 × 1000)
= 0.1413 m³
10.2 Water volume
Volume of water:
= 150 / (1.00 × 1000)
= 0.1500 m³
10.3 Admixture volume
Admixture volume:
= 2.67 / (1.09 × 1000)
= 0.00245 m³
10.4 Volume of aggregate
Volume of aggregate:
= 1 − (volume of cement + volume of water + volume of admixture)
= 1 − (0.1413 + 0.1500 + 0.00245)
= 0.7063 m³
10.5 Coarse aggregate quantity
20 mm aggregate
= 0.7063 × 0.59 × 2.69 × 0.50 × 1000
= 560.5 kg/m³
12.5 mm aggregate
= 0.7063 × 0.59 × 2.69 × 0.50 × 1000
= 560.5 kg/m³
10.6 Fine aggregate quantity
Crushed stone sand:
= 0.7063 × 0.41 × 2.60 × 1000
= 752.9 kg/m³
11. Final Initial Trial Mix
| Material | Quantity per m³ |
|---|---|
| OPC 53 cement | 445 kg |
| 20 mm coarse aggregate | 560.5 kg |
| 12.5 mm coarse aggregate | 560.5 kg |
| Crushed stone sand | 752.9 kg |
| Free water | 150 litres |
| Fosroc Auramix 400 | 2.67 kg |
| Actual water-cement ratio | 0.337, approximately 0.34 |
| Theoretical concrete density | 2,471.5 kg/m³, approximately 2,472 kg/m³ |
Approximate mass ratio
The approximate material ratio by mass, with cement taken as 1, is:
Cement : 20 mm aggregate : 12.5 mm aggregate : crushed stone sand
= 1 : 1.26 : 1.26 : 1.69
This is only a representation of the calculated trial mix. It is not a nominal mix ratio and must not replace the designed quantities or trial-mix approval.
12. Moisture and Absorption Correction
The calculated quantities are based on saturated surface-dry aggregate conditions. The stated free surface moisture is nil, while the aggregates have measurable absorption.
An approximate absorption-water requirement, if the aggregates are significantly below saturated surface-dry condition, is:
| Aggregate | Quantity | Absorption | Illustrative absorption water |
|---|---|---|---|
| 20 mm aggregate | 560.5 kg | 0.37% | 2.07 litres |
| 12.5 mm aggregate | 560.5 kg | 0.54% | 3.03 litres |
| Crushed stone sand | 752.9 kg | 2.35% | 17.69 litres |
| Total | 22.79 litres |
The 22.79 litres is only an illustrative absorption demand if the aggregate condition justifies it. It should not be automatically added to the batch water.
Actual correction must be based on:
- Measured moisture content
- Water absorption
- Aggregate stockpile condition
- Whether the aggregate is oven-dry, air-dry, damp or SSD
- Batch-plant weighing practice
The batch water should be corrected so that the intended free water remains approximately 150 litres/m³.
13. Trial-Mix and Quality-Control Requirements
Before approving the mix for production, carry out laboratory and site trials using the actual materials.
Check the following:
- Slump immediately after mixing.
- Slump retention at the required delivery time.
- Concrete temperature.
- Segregation and bleeding.
- Pumpability through the proposed pipeline.
- Fresh concrete density and yield.
- Admixture compatibility and setting time.
- Cube compressive strength at 7 and 28 days.
- Moisture correction for every aggregate fraction.
- Batch-to-batch consistency.
- Concrete finishability and surface appearance.
- Strength and durability requirements of the project.
Do not add water at site to correct slump without approval. Slump adjustments should normally be controlled through the approved admixture procedure and documented trial results.
14. Common Errors to Avoid
- Writing “Fosroc Auromix” instead of “Fosroc Auramix 400.”
- Referring to aggregate grading as “IS 383 Table 2.”
- Writing
0.59%instead of the coarse aggregate volume fraction0.59. - Calling the calculation a fixed M55 mix ratio.
- Treating 69 MPa as a universal target mean strength.
- Using 12 mm when the tested aggregate size is 12.5 mm.
- Ignoring aggregate moisture and absorption.
- Using the same mix for pumping and bucket placement without trials.
- Treating chemical admixture as cementitious binder.
- Using calculated SSD quantities directly without field moisture correction.
- Adding water at site without checking the approved water-cement ratio.
- Approving the mix without 7-day and 28-day strength results.
15. Frequently Asked Questions
Is this the final M55 concrete mix?
No. It is an initial trial mix based on the stated materials and assumptions. The final production mix requires laboratory and site verification.
Why is the target strength shown as 69 MPa?
The value 69 MPa comes from applying a 14 MPa project or MoRTH-specific margin to M55. It should only be used when required by the governing project specification.
Why is the adopted cement content 445 kg/m³?
Using 150 litres of water and a water-cementitious ratio of 0.34 gives approximately 441.2 kg/m³. The value is rounded upward to 445 kg/m³ and remains within the stated 380–450 kg/m³ range.
Can this mix be used for bucket placement?
Not automatically. The calculation uses pumping as the governing placement method. Bucket placement should be confirmed through a separate trial.
Can river sand be substituted for crushed stone sand?
No direct substitution should be made. A change in fine aggregate requires new grading, moisture, absorption, workability and trial-strength checks.
Why is the actual water-cement ratio 0.337 instead of exactly 0.34?
The selected design ratio was used to calculate approximately 441.2 kg/m³ of cement. The adopted cement was rounded to 445 kg/m³, so the actual ratio becomes:
150 / 445 = 0.337
16. Related Resources
- Concrete Mix Design Hub
- Concrete Mix Design Calculator as per IS 10262:2019
- Target Mean Strength of Concrete
- Water-Cement Ratio in Concrete
- Moisture Correction in Concrete Mix Design
- Superplasticizer in Concrete Mix Design
- Concrete Trial Mix Procedure
- Fresh Concrete Density and Yield
Conclusion
The calculated initial M55 trial mix per cubic metre is:
- Cement: 445 kg
- 20 mm aggregate: 560.5 kg
- 12.5 mm aggregate: 560.5 kg
- Crushed stone sand: 752.9 kg
- Free water: 150 litres
- Fosroc Auramix 400: 2.67 kg
- Actual water-cement ratio: approximately 0.337
- Theoretical concrete density: approximately 2,472 kg/m³
These quantities are valid only for the stated materials, grading, specific gravities, moisture condition, admixture dosage and design assumptions. Final approval requires trial-mix testing and project-authority acceptance.
About T Square Civil Engineering
T Square Civil Engineering provides practical civil-engineering explanations, concrete technology guidance, construction calculations and site-oriented learning resources. The content connects engineering theory with construction practice, testing, quality control and field application—from Theory to Construction Practice.
Disclaimer
The information on this website is provided for educational purposes only.
It does not replace project-specific engineering design, professional advice, approved drawings or construction specifications. Examples, calculations and suggested procedures should not be adopted directly for construction without appropriate verification. Always check the latest applicable standards and amendments, local requirements, project specifications, material-test results and site conditions. Final design, testing, acceptance and construction decisions should be made by qualified professionals and the responsible project authorities.
T Square Civil Engineering is an independent educational platform and is not affiliated with BIS, MoRTH, IRICEN, Fosroc, UltraTech Cement or any other organization mentioned on this page.
