Concrete mix design is a critical process in construction, ensuring the right balance of strength, durability, and workability. For high-strength applications like bridges, high-rise buildings, and industrial floors, M35 grade concrete is a popular choice.
In this guide, we’ll break down the step-by-step mix design for M35 concrete, backed by factual data and practical insights. No fluff—just actionable information you can use on-site.
Understanding M35 Grade Concrete
M35 signifies that the concrete has a characteristic compressive strength of 35 MPa (N/mm²) at 28 days. This grade is commonly used in:
- Heavy-duty pavements
- Pre-stressed concrete structures
- High-rise building columns and slabs
- Marine structures (with additional durability considerations)
To achieve this strength, the mix must be carefully proportioned using quality materials and precise calculations.
Grade of Concrete : M35
Characteristic Strength (Fck) : 35 Mpa
Standard Deviation : 1.91 Mpa*
Target Mean Strength : T.M.S.= Fck +1.65 x S.D.
(from I.S 456-2000) = 35+ 1.65×1.91
= 38.15 Mpa
Materials Required for M35 Concrete Mix
1. Cement
- Type: Ordinary Portland Cement (OPC 53 Grade)
- Why OPC 53? Higher early strength gain compared to OPC 43.
- Standard: IS 12269 (1987)
2. Fine Aggregate (Sand)
- Type: Natural river sand or crushed stone sand (Zone II recommended)
- Fineness Modulus: 2.6 to 3.0
- Silt Content: ≤ 3% (as per IS 383)
3. Coarse Aggregate
- Size: 20mm (nominal max size)
- Shape: Angular/cubical for better interlocking
- Specific Gravity: ~2.7
- Water Absorption: < 1% (to avoid excess water demand)
4. Water
- Quality: Potable water (pH 6–8, conforming to IS 456)
- Water-Cement Ratio (w/c): 0.40–0.45 (critical for M35 strength)
5. Admixtures (Optional but Recommended)
- Superplasticizers (Polycarboxylate Ether-based): Improves workability without extra water.
- Dosage: 0.5–1.2% by weight of cement (as per manufacturer guidelines)
MIX DESIGN
Take Sand content as percentage of total aggregates = 36%
Select Water Cement Ratio = 0.43 for concrete grade M35
(From Fig 2. of I.S. 10262- 1982)
Select Water Content = 172 Kg
(From IS: 10262 for 20 mm nominal size of aggregates Maximum Water Content = 186 Kg/ M3 )
Hence, Cement Content= 172 / 0.43 = 400 Kg / M3
Formula for Mix Proportion of Fine and Coarse Aggregate:
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +(Fa / Sp. Gr.* Pf )}
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +Ca / Sp. Gr.* Pc )}
Where Ca = Coarse Aggregate Content
Fa = Fine Aggregate Content
Pf = Sand Content as percentage of total Aggregates
= 0.36
Pc = Coarse Aggregate Content as percentage of total Aggregates.
= 0.64
a0 = Percentage air content in concrete (As per IS :10262 for 20 mm nominal size of
aggregates air content is 2 %) = 0.02
Hence, 1000(1-0.02) = {(400 /3.15) + 172 +(Fa / 2.62 x 0.36)}
Fa = 642 Kg/ Cum
As the sand is of Zone II no adjustment is required for sand.
Sand Content = 642 Kg/ Cum
1000(1-0.02) = {(400 /3.15) + 172 +(Ca / 2.67 x 0.64)}
Hence, Ca = 1165 Kg/ Cum
From combined gradation of Coarse aggregates it has been found out that the proportion of 53:47 of 20 mm & 10 mm aggregates produces the best gradation as per IS: 383.
Hence, 20 mm Aggregates = 619 Kg
And 10 mm Aggregates = 546 Kg
To obtain slump in the range of 150-190 mm water reducing admixture brand SP430 from Fosroc with a dose of 0.3 % by weight of Cement shall be used.
Hence the Mix Proportion becomes:
| Cem | W/C | Water | Sand | 20mm | 10mm | Admix |
| 400 | 0.43 | 172 | 635 | 619 | 564 | 1.2 |
| 1 | 0.43 | 1.6 | 1.547 | 1.36 | 0.003 |
Units – Kg/ M3
Cement : Sand: Coarse Aggregates = 1 : 1.6 : 2.907