Concrete Mix Proportioning —
Guidelines
The definitive standard for designing concrete mixes from M10 to M80. This code provides a systematic, step-by-step procedure to proportion cement, water, fine aggregate, and coarse aggregate to achieve the required strength, workability, and durability.
📋 2019 Revision: The 2019 edition extends the scope to M80 grade concrete, adds provisions for supplementary cementitious materials (SCM), and updates the standard deviation table. It supersedes IS 10262:2009 in its entirety.
IS 10262:2019 provides guidelines for proportioning concrete mixes for normal, standard, and high-strength concrete from M10 to M80. It covers the following cement types:
Design Mix vs. Nominal Mix IS 10262 governs design mixes only. Nominal mixes (1:2:4, 1:1.5:3 etc.) are permitted by IS 456 only up to M20 for non-structural or minor structural work. For all structural concrete M25 and above, a design mix per IS 10262 is mandatory.
The following information must be established before starting the mix proportioning procedure:
| Input | Source / Reference |
|---|---|
| Characteristic compressive strength (fck) | Project specification |
| Standard deviation (s) | IS 10262 Table 1 (or from site records) |
| Exposure condition | IS 456 Table 3 |
| Workability (slump or Vee-Bee) | IS 456 Table 11 / project spec |
| Nominal maximum aggregate size | IS 383 / project spec |
| Type and grade of cement | IS 269 / IS 1489 / IS 455 |
| Specific gravity of materials | Laboratory test (IS 2386) |
When sufficient site data is unavailable, the following assumed standard deviations from IS 10262 Table 1 shall be used:
| Grade of Concrete | Standard Deviation s (N/mm²) |
|---|---|
| M10 to M15 | 3.5 |
| M20 to M25 | 4.0 |
| M30 to M35 | 5.0 |
| M40 to M50 | 6.0 |
| M55 to M80 | 6.0 |
Use Site Data When Available The tabulated values assume good quality control. Once 30 or more test results are available from the site, calculate the actual standard deviation and use it instead. A lower s from good QC reduces the target mean strength and saves cement.
Calculate f'ck = fck + 1.65s using the standard deviation from Table 1 or site records. This is the strength the mix must achieve on average to ensure 95% of results exceed fck.
Select w/c ratio from IS 10262 Table 5 (strength vs. w/c relationship for the cement type). Then verify it does not exceed the maximum w/c ratio from IS 456 Table 5 for the given exposure condition. Use the lower of the two values.
Obtain the approximate water content from IS 10262 Table 2, based on nominal maximum aggregate size and target slump. Adjust for aggregate shape (angular vs. rounded) and admixture use.
Cement content = Water content / w/c ratio. Check that this is not less than the minimum cement content specified in IS 456 Table 5 for the exposure condition. Also check it does not exceed 450 kg/m³ (to control heat of hydration).
Obtain the volume fraction of coarse aggregate from IS 10262 Table 3, based on the nominal maximum aggregate size and the zone of fine aggregate (IS 383). Adjust for w/c ratio using the correction factor in the table footnotes.
Total volume = 1 m³. Subtract volumes of cement, water, coarse aggregate, and air (typically 1–2%) to obtain the volume of fine aggregate. Multiply by specific gravity of FA to get mass.
Prepare at least three trial mixes with ±10% variation in w/c ratio. Measure actual slump and cast cubes for 7-day and 28-day strength. Adjust proportions to achieve target workability and strength simultaneously.
Superplasticizers (high-range water reducers) are commonly used to reduce the water content while maintaining workability. Their effect must be accounted for in the mix design:
| Admixture Type | Typical Water Reduction | Effect on Mix |
|---|---|---|
| Normal plasticizer | 5–10% | Reduces water; slightly improves workability |
| Superplasticizer (HRWR) | 20–30% | Significant water reduction; same slump at lower w/c |
| Retarder | — | Extends setting time; useful in hot weather |
| Accelerator | — | Speeds setting; used in cold weather or precast |
Adjust Water Content for Admixtures When a superplasticizer is used, reduce the free water content by the percentage stated by the manufacturer (typically 20–30%). Recalculate cement content and aggregate volumes accordingly. Do not simply add the admixture to the base mix without adjusting water.
Design a concrete mix for M25 grade, moderate exposure, 20 mm nominal maximum aggregate size, target slump 75 mm, using OPC 53 grade cement.
| Step | Parameter | Value | Source |
|---|---|---|---|
| 1 | Characteristic strength fck | 25 N/mm² | Specified |
| 1 | Standard deviation s | 4.0 N/mm² | IS 10262 Table 1 |
| 1 | Target mean strength f'ck = 25 + 1.65 × 4.0 | 31.6 N/mm² | Cl. 3.2 |
| 2 | w/c ratio (from Table 5 for 31.6 N/mm²) | 0.50 | IS 10262 Table 5 |
| 2 | Max. w/c for moderate exposure (IS 456) | 0.50 | IS 456 Table 5 |
| 2 | Adopted w/c ratio | 0.50 | Min. of above |
| 3 | Water content (20 mm agg., 75 mm slump) | 186 kg/m³ | IS 10262 Table 2 |
| 4 | Cement content = 186 / 0.50 | 372 kg/m³ | Calculated |
| 4 | Min. cement for moderate exposure (IS 456) | 300 kg/m³ | IS 456 Table 5 ✓ |
| 5 | Vol. fraction of CA (Zone II FA, w/c 0.50) | 0.62 | IS 10262 Table 3 |
| 5 | Coarse aggregate (SG 2.74) | 1,101 kg/m³ | Calculated |
| 6 | Fine aggregate (SG 2.65, by abs. vol.) | 631 kg/m³ | Calculated |
Always Do Trial Mixes The above proportions are a starting point. Prepare trial batches, measure actual slump, and cast 150 mm cubes. Test at 7 days (target ≥ 67% of f'ck) and 28 days. Adjust w/c and aggregate proportions as needed before finalising the mix.