Determination of initial degree of hydration by means of ultrasonic measurements

For the prediction of the mechanical properties of early age concrete, as well as for the prediction of thermal stresses it is essential to know the initial degree of hydration, at which the development of stiffness and strength begins. This paper deals with the problem of determination of the end of this inactive phase, called dormant phase. Using compressional wave and shear wave transducers the hardening of concrete is observed under adiabatic and isothermal curing conditions. From the development of dynamic Young’s modulus and Poisson’s ratio a model of the initial degree of hydration is derived to improve existing models of the development of tensile strength and modulus of elasticity for very early age concrete. Typical results are presented for different concrete compositions, especially for high strength concrete.