Concrete Compressive Strength f'c

f_{c}^{'} = 28-day cylinder strength (6\times12 in)

Specified compressive strength f'c is measured on standard cylinders (US: 6×12 in or 4×8 in) at 28 days unless noted. Design uses φ and 0.85 f'c in Whitney. Typical 3000–6000 psi (20–40 MPa). Modulus of rupture / splitting tensile ≈ 7.5 λ √f'c psi.

$f_{c}^{'}$ (psi): Specified compressive strength
$f_{r}$ (psi): Modulus of rupture

Step-by-step solved example

f'c = 4000 psi. Approximate modulus of rupture fr = 7.5 √f'c (normalweight, λ = 1)?

f'c from a cylinder; Whitney uses 0.85 f'c on the block.

1. Root
√4000 = 63.25.
2. fr
fr = 7.5×63.25 = 474 psi.
$f_{r} = 474 psi$

Answer: 474 psi

10 practice questions

0/10 correct

1.US standard cylinder is commonly

2.f'c is usually specified at

3.Higher w/c generally

4.fr ≈ 7.5 √f'c is in

5.A cube strength is typically

6.4000 psi is about

7.λ for lightweight concrete is

8.f'c is used in Whitney as

9.Air entrainment typically

10.A 6×12 cylinder fails at 118 kip. f'c nearest