Determination of the Apparent Activation Energy of Concrete: Ea. Semi-Adiabatic Tests of Heat Development

The "method of equivalent age" is one of the currently used nondestructive testing methods of concrete strength estimation. It is based on Arrhenius' law, which has shown itself to be the most accurate in describing the influence of temperature on concrete strength development at early ages. A proper estimation is directly related to a correct determination of the Apparent Activation Energy: Ea. This is the unique parameter which characterizes the concrete mixture and which can be found in Arrhenius' law. The major aim of this paper is to show how calorimetric tests under semi-adiabatic conditions can be an alternative to unwieldy compressive test procedures in determining Ea. The validity of the obtained Ea values has been verified by means of several mechanical tests. Moreover, the possibility of using either mortar or concrete is partially dealt with. The water to cement ratio appears to naturally be considered as a constant in proportioning an equivalent mortar. Finally, the evolution of the Apparent Activation Energy in relation to the degree of hydration is given. Hence, the widespread opinion that Ea depends on the degree of hydration is confirmed and a field of definition can be brought to the fore.