CONCRETE
Modulus of Elasticity of Concrete (Ec)
Short-term static modulus of elasticity of concrete per IS 456 Cl. 6.2.3.1 — Ec = 5000√fck (in N/mm² with fck in N/mm²).
Also calledmodulus of elasticityec concreteyoung's modulus concreteelastic modulus concreteis 456 ec
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CODES
Definition
Per IS 456 Cl. 6.2.3.1, the short-term static modulus of elasticity Ec = 5000√fck N/mm², where fck is characteristic compressive strength at 28 days. Long-term modulus Ec,long ≈ Ec / (1 + θ), where θ is creep coefficient (typically 1.6 for normal-weight concrete in moderate environment).
Typical values
M20 (fck=20)Ec = 22,360 N/mm² ≈ 22 GPa
M25 (fck=25)Ec = 25,000 N/mm² = 25 GPa
M30 (fck=30)Ec = 27,386 N/mm² ≈ 27 GPa
M35 (fck=35)Ec = 29,580 N/mm² ≈ 30 GPa
M40 (fck=40)Ec = 31,623 N/mm² ≈ 32 GPa
M50 (fck=50)Ec = 35,355 N/mm² ≈ 35 GPa
Long-term factor (creep θ=1.6)Ec,long ≈ Ec / 2.6
Where used
- Deflection calculation (Annex C)
- Crack-width estimation
- Soil-structure interaction analysis
- Dynamic / modal analysis
Acceptance / threshold
Per IS 456 Cl. 6.2.3.1 — Ec = 5000√fck for short-term; reduce by creep for long-term deflection check.
Site example
M30 column: Ec = 5000 × √30 = 27,386 N/mm² for short-term static analysis. For long-term deflection: Ec,long = 27386 / (1+1.6) = 10,533 N/mm² ≈ 10.5 GPa.
Frequently asked
Formula for Ec of concrete?
Per IS 456 Cl. 6.2.3.1: Ec = 5000√fck (in N/mm²) where fck = characteristic cube strength at 28 days. M25 → Ec = 25 GPa; M30 → Ec ≈ 27 GPa.
Why is long-term Ec lower than short-term?
Concrete creep — sustained load causes additional strain over time. Long-term Ec = Ec / (1+θ), where θ is creep coefficient (typically 1.6 for normal-weight concrete in moderate humidity).
Related concrete terms
Concrete Mix Design
Proportioning of cement, water, aggregates per IS 10262
Concrete Grades (M15-M80)
M20=20 N/mm² characteristic strength at 28 days
Water-Cement Ratio (w/c)
Mass of water to mass of cement. 0.40-0.55 typical.
Concrete Cover
Min concrete from rebar to surface (15-50mm per exposure)
Concrete Curing
Min 7 days for OPC, 10 days for PPC, 14 days for sulphate-resistant
Slump Test / Workability
25-150mm slump per application (IS 1199)
Cube Test (Compressive Strength)
150mm cube compressive strength test at 7/28 days (IS 516)
Concrete Admixtures
Plasticizers, accelerators, retarders per IS 9103