WORKED MIX DESIGN EXAMPLE

M25 concrete ratio and mix design

Calculate an M25 example with visible water/binder selection, ingredient quantities, 28-day target strength and all eight mix design steps.

M25 · Moderate exposureReinforced concrete · OPCIllustrative materials · Not a tested mix

Scale the worked example

Required concrete volume · m³

This M25 example connects the higher mean-strength target to a preliminary water/cement ratio, then shows how water demand determines cement content. All quantities come from the same calculation engine as the main lab.

All material assumptions are listed below. Open the full lab to change them.

M20 example →M30 example →

YOUR M25 EXAMPLE · BATCH QUANTITIES

2,451.81kg for 1 m³ designed concrete

Target mean strength31.6 MPa

Final water / cement0.48

SSD ratio by mass1 : 2.2 : 3.77

Ratio is total binder : fine aggregate : coarse aggregate for this example. Batch weights below use the entered aggregate moisture.

Material	Your batch · kg
Cement	328.6
Fine aggregate (as batched)	722.47
Coarse aggregate (as batched)	1,239.72
Water to add at mixer	157.73
Chemical admixture	3.29

Adjust this M25 design in the lab →

Following strength selection through to binder demand

Grade is the characteristic concrete strength; it is not the average target used for proportioning. The selected cement-strength reference is a separate material assumption. Its graph is an approximate starting aid, so a ratio chosen from it must be checked with the actual cement and aggregates.

Moderate exposure is the selected brief here. Strength, durability and workability need to be satisfied together. The assumed water reduction must be demonstrated by compatible admixture trials; a dosage percentage does not itself establish the reduction.

Material and design assumptions

Slump / aggregate: 100 mm / 20 mm angular, Zone II
Specific gravities: Cement 3.15; sand 2.65; stone 2.74
Entrapped air: 1% of concrete volume
Water reduction / dosage: 20% trial assumption / 1% of binder
Sand: absorption / moisture: 1% / 1% of oven-dry mass
Stone: absorption / moisture: 0.5% / 0.5% of oven-dry mass
Cement-strength curve: Expected cement strength 43 to <53 MPa; approximate reference
Admixture SG / water fraction: 1.145 / 0% — replace with supplier data
Binder / statistical basis: OPC only; assumed standard deviation; good control

These are example inputs, not a material test certificate. No fly ash, GGBS, silica fume, pump reduction or binder uplift is applied. The reference ratio is selected from the approximate curve, rounded down to 0.01 and checked against the selected durability cap.

Can M25 use an IS 456 nominal mix recipe?

The nominal-mix provision in clause 9.3 is limited to M20 or lower. Use a designed-mix process for M25, including constituent testing, workability checks and strength trials. Do not promote a fixed 1:1:2 proportion as a universal M25 design.

Follow the M25 calculations

1. Set the target mean strength

IS 10262:2019 · 4.2, Tables 1–2

f′ck = max(fck + 1.65S, fck + X)max(25 + 1.65 × 4.00, 25 + 5.50) = 31.60 MPa

Assumed standard deviation 4.00 MPa. The larger margin governs; characteristic and target strengths are different.

2. Select and check the water/binder ratio

IS 10262 · 5.1 / IS 456 · Table 5

r = min(strength-based ratio, durability limit)min(0.48, 0.50) = 0.48

The ratio is interpolated from approximate Figure 1 readings and rounded down to 0.01. It is a preliminary selection, not a measured strength prediction.

3. Estimate the free water

IS 10262 · 5.3, Table 4

W = (W₀ − shape adjustment) × slump factor × (1 − reduction)(186 − 0) × 1.060 × 0.80 = 157.7 kg/m³

The starting water estimate is for SSD aggregates. The 3% change per 25 mm slump and admixture reduction are preliminary; actual workability must be measured.

4. Calculate and allocate the binder

IS 10262 · 5.4 / IS 456 · Tables 5–6

B = max((W ÷ r) × trial increase, durability minimum)max((157.73 ÷ 0.48) × 1.00, 300.00) = 328.6 kg/m³

Final w/b is 0.480 after minimum-content or trial adjustments. Replacement percentages are fractions of total binder mass.

5. Close the absolute-volume balance

IS 10262 · 5.2, 5.7

Vagg = 1 − Vair − Σ [mᵢ ÷ (Gᵢ × 1000)]1 − 0.0100 − 0.2649 = 0.7251 m³

Use specific gravity, not loose bulk density. Water carried inside the chemical admixture is counted once, within that product’s volume.

6. Split the aggregate volume

IS 10262 · 5.5, Table 5

pCA = [p₀ + 0.2(0.50 − w/b)] × (1 − reduction)[0.62 + 0.2 × (0.50 − 0.480)] × 1.00 = 62.4% coarse / 37.6% fine

SSD masses: fine 722.5 kg and coarse 1239.7 kg per m³. The optional reduction is a trial adjustment up to 10%, not an automatic pumpability guarantee.

7. Correct for aggregate moisture

SSD mass balance · IS 10262 Annexes A–B

mOD = mSSD/(1+A); mwet = mOD(1+MC); Wsurface = mOD(MC−A); Wmixer = Wfree − Wsurface,sand − Wsurface,stone − Wadmixture

Sand surface water: 715.3 × (1−1)/100 = 0.00; stone surface water: 1233.6 × (0.5−0.5)/100 = 0.00; mixer water: 157.73 − (0.00) − (0.00) − 0.00 = 157.7 kg/m³ mixer water

All water quantities above are kg per m³. A and MC are fractions in the formula; entered percentages are divided by 100. Total moisture and absorption use an oven-dry mass basis. Surface water 0.0 kg plus admixture water 0.0 kg is deducted from the free-water budget. Negative surface water represents aggregate absorption demand.

8. Scale and test the trial batch

IS 10262 · 5.8

Batch quantity = quantity per m³ × batch volumeEach constituent × 1.000 m³ = 1.000 m³ trial batch

Measure workability, fresh density, yield and strength; inspect segregation and bleeding. Revise the mix and record trials before project approval.

Checks and assumptions to review

Admixture water contribution is set to 0%. Enter the supplier’s measured water fraction when applicable; do not assume a liquid product is water-free.

Method: IS 10262:2019; selected durability provisions: IS 456:2000. BIS-authored third-party source copies. Verify applicable editions, amendments and project requirements. No independent professional approval is claimed.