Dynamic Modulus for Reinforced Concrete Beams

The modulus of elasticity of concrete given by ACI Code 318-83 is thought of as secant modulus under static loads. It is more appropriate to use modulus of elasticity of concrete measured by a dynamic system, where dynamic loads are involved. The transverse vibration and elastic wave propagation methods are used to get the dynamic elastic modulus. The results from six reinforced concrete beams in three pairs, each pair consisting of two identical beams, are presented. Being nondestructive these tests can be used repeatedly on the same specimen to study aging, durability, resistance to frost, etc. It is found that the Code value of modulus of elasticity for concrete agrees more with the value of dynamic modulus obtained from transverse vibration method than that obtained from stress propagation method. This may be due to the nonhomogeneous nature of concrete and the presence of steel bars in the beams. The stress propagation method can be used for quality control of concrete products because the pulse velocity depends only on the elastic property of the material and not on the geometry.