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Concrete Properties

Courses > Reinforced Concrete Design > General Topics > Concrete Properties


Introduction on Concrete Properties :

Concrete has relatively high compressive strength, but significantly lower tensile strength, and as such is usually reinforced with materials that are strong in tension (often steel). The elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete has a very low coefficient of thermal expansion, and as it matures concrete shrinks. All concrete structures will crack to some extent, due to shrinkage and tension. Concrete which is subjected to long-duration forces is prone to creep.



Concepts and Formulas of Concrete Properties:

 

Typical properties of normal strength Portland cement concrete:

Compressive strength of concrete (% of 28-day strength) vs age (days)

The American Concrete Institute (ACI) suggests the following equation for the modulus of elasticity:

E_{c} = 33omega _{c}^{1.5}sqrt{f'_{c}}; (psi)

where

wc = weight of concrete (pounds per cubic foot)

f'c = compressive strength of concrete at 28 days (psi)

 AASHTO Load and Resistance Factor Design Manual, or "LRFD"  suggests the following equation:

E_{c} = 33000K_{1}omega _{c}^{1.5}sqrt{f'_{c}}; (ksi)

where

K1 = correction factor for aggregate source (taken as 1.0 unless determined otherwise)

wc = weight of concrete (pounds per cubic foot (pcf))

f'c = compressive strength of concrete at 28 days (psi)

A handy approximate equation:

E_{c} = 1820sqrt{f'_{c}}; (ksi)


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