CONCRETE DYNAMIC MODULUS - INFLUENCE OF DRYING AND REWETTING

The dynamic modulus of elasticity of concrete is an important variable . The dynamic modulus in itself is not used in design; however, its im portance is derived from the fact that it can be measured quite accura tely using non-destructive tests, and it has been successfully correla ted with other strength variables. Measurement of the dynamic modulus non-destructively allows the monitoring of the concrete strength in si tu and in laboratory specimens with very small statistical variability . In this study, the effect of drying in several environmental conditi ons on the dynamic modulus of concrete containing superplasticizers (S Ps) is investigated. SPs are used frequently in concrete casting, espe cially in hot arid climates, to compensate for the loss of workability due to water evaporation. In addition, after the concrete has been dr ied 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 tempe rature to 100-degrees-C grade, with the relative humidity kept at arou nd 20%. The dynamic modulus of the concrete is monitored over time via two non-destructive techniques. The first is the resonant frequency m ethod which gives quite accurate results for the dynamic modulus, and the second is the pulse velocity method which is popular but less accu rate. A comparison is made between the values obtained by the two meth ods.