Concrete f'c from Modulus of Elasticity (ACI 318-19 19.2.2)
Back out the equivalent in-place f'c from a measured or specified stiffness.
Example
You enter
- Elastic modulus Ec (psi) 3644147
- Unit weight wc (pcf, 145 normalweight) 145
You get
- Fc (psi) 4000
Details, formula, and sources
f'c = (Ec / (wc^1.5 x 33))^2. An Ec of 3,644,000 psi at 145 pcf implies ~4,000 psi. Useful from a resonance / sonic-modulus test; not a cylinder-break value. A design aid; the engineer of record's stamped design governs.
f'c = (Ec / (wc^1.5 x 33))^2, the ACI 318-19 19.2.2.1(a) relation Ec = wc^1.5 x 33 x sqrt(f'c) solved for the compressive strength (90 <= wc <= 160 pcf).
The ACI 318-19 19.2.2.1 modulus of elasticity of concrete, solved for f'c, by name.
ACI 318 is readable free through the ACI online reading room at concrete.org; the 19.2.2 modulus provisions are in the published code.
Estimate. AHJ and licensed professional govern.
Field names used by the API: ec_psi, wc_pcf, fc_psi
- Secant modulus inverted f'c = (Ec / (wc^1.5 x 33))^2 for 90 <= wc <= 160 pcfACI 318-19 19.2.2.1(a)
- Equivalent strength an equivalent in-place f'c from a stiffness, not a cylinder-break valuescope of this tile
- Design value the in-place modulus varies with aggregate and mixscope of this tile