Concrete f'c from Modulus of Elasticity (ACI 318-19 19.2.2)
The inverse of the elastic-modulus tile: back out the equivalent in-place f'c from a measured or specified stiffness, 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.
Formula and source
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.
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