During the first hours after mixing, the properties of concrete vary and change within a wide range of behaviour. Fresh concrete is more or less a Newtonian fluid gradually changing into a Bingham type of material, finally attaining solid body properties with considerable compressive strength and stiffness. The development of mechanical properties can be described by the degree of hydration. For the prediction of mechanical properties of early age concrete as well as for the prediction of stresses caused by differences of temperature and autogenous shrinkage, it is essential to know the initial degree of hydration, from which on the development of strength and stiffness begins. This paper deals with the determination of the end of the dormant phase by using ultrasonic pulse velocity techniques.
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