Characterization of Fresh Mortar with Chemical Admixtures Based on Stress Wave Dispersion

The performance of any concrete structure strongly depends on the quality of the fresh material used. This quality should be evaluated at an age as early as possible, even before concrete is placed in the forms. In the present paper fresh cementitious material is examined by means of ultrasonic through-transmission measurements. The frequency is varied in order to apply different wavelengths, the propagation of which is influenced in a different way by the constituent materials, e.g. air bubbles and sand grains. The wave velocity vs. frequency curves obtained for different mixes show that the existence of sand plays an important role due to interaction with different wave lengths. The effect of chemical admixtures is also examined through the release of air bubbles and the change in viscosity they impose. The possibility to characterize the effectiveness of chemical admixtures by a single measurement of dispersion is discussed.