Multi-geophysical approach for characterization of thermally-induced cracks in granite: discussion of repetitivity and durability

In this work, we propose an experimental study to characterize micro-scale damage introduced in a granite with two different thermal treatments performed at low temperature: the slow cooling and the thermal shock. Damage is characterized by monitoring of elastic wave velocity and thermal conductivity. The same protocol is performed on 5 samples in order to discuss the repetitivity of the induced damage. It is observed that the thermal shock protocol leads to a more pronounced damage interpreted in terms of a larger variety of nu-cleated intragranular and intergranular cracks, that were observed by microscopes. However, this more important damage seems not to be repetitive from one sample to another compared to the damage introduced by slow cooling. Following this first result, a time follow-up for wave velocity, conductivity and mercury porosity is proposed. It appears that the damage introduced by the slow cooling, unlike the thermal shock, does not present a long durability. After 15 days, the different properties had returned to their initial state. A time-dependence mechanism is proposed to discuss this observed process.