The modulus of elasticity of concrete is given by Ec = ........... MPa (where fck = characteristic compressive strength of the concrete cube).
Try it first: pick an option, then read the explanation.
Correct answer: D. 5000 √fck
Modulus of Elasticity Formula — IS 456:2000
IS 456:2000 gives the short-term static modulus of elasticity of concrete as:
Ec = 5000 √fck (MPa)where fck is the characteristic compressive strength of concrete in N/mm². Note the square root — confusing this with a linear relationship (e.g., 5000 fck) is a common exam mistake. The older IS 456:1978 used 5700 √fck, but the current code uses 5000 √fck.
Ec = 5000 √fck MPa — option D.
Key takeaway
IS 456:2000 → Ec = 5000 √fck. It’s always the square root, and always 5000 (not 3000 or 2000).