1563Modulus of Elasticity

To appreciate the differences in code expressions for the modulus of elasticity of concrete, it is important to realize that both ACI 318-02 and EC2-02 use a secant modulus. The definition of the secant modulus, however, is different in the two codes; and the ACI 318-02 bases the modulus on the specified compressive strength, whereas EC2-02 bases the modulus on the average compressive strength. ACI 318-02 gives an expression for the secant modulus of elasticity — defined as the slope of a line drawn from a stress of zero to a compressive stress equal to 0.45f — and given as

Ec = 0.043wcL5yTc MPa where wc is the concrete unit weight varying from 90 to 155 lb/ft3 (1500 to 2500 kg/m3). For normal density concrete, the expression simplifies to

Ec = 4700 Vf7 MPa

EC2-02 gives the following expression for the secant modulus — defined as the slope of a line drawn from a stress of zero to a compressive stress equal to 0.40fcm

CSA A23.3-94 and NZS 3101-95 adopted slightly modified versions of an equation based on the research by Carrasquillo et al. [77] and reported by ACI Committee 363 [78]:

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