Concrete dynamic modulus: influence of drying and rewetting

Abstract

The dynamic modulus of elasticity of concrete is an important variable. The dynamic modulus in itself is not used in design; however, its importance is derived from the fact that it can be measured quite accurately using non-destructive tests, and it has been successfully correlated with other strength variables. Measurement of the dynamic modulus non-destructively allows the monitoring of the concrete strength in situ and in laboratory specimens with very small statistical variability. In this study, the effect of drying in several environmental conditions on the dynamic modulus of concrete containing superplasticizers (SPs) is investigated. SPs are used frequently in concrete casting, especially in hot arid climates, to compensate for the loss of workability due to water evaporation. In addition, after the concrete has been dried for some time the effect of rewetting the specimens on the dynamic modulus is investigated. Specimens with and without superplasticizers are cast and cured then dried in temperatures ranging from room temperature to 100°C grade, with the relative humidity kept at around 20%. The dynamic modulus of the concrete is monitored over time via two non-destructive techniques. The first is the resonant frequency method which gives quite accurate results for the dynamic modulus, and the second is the pulse velocity method which is popular but less accurate. A comparison is made between the values obtained by the two methods.