Damage of basalt induced by microwave irradiation

In this work microwave irradiation on cylindrical samples of basaltic rock is investigated by laboratory experiments and compared with results from numerical models. Due to the temperature gradient in the samples induced by the microwave irradiation a significant damage indicated by a reduction of the sound velocity and finally the formation of cracks occurs. Applying a microwave power of 3.2 kW leads to a surface temperature of 250 °C and to 400 °C in the centre of a cylindrical sample after 60 s of irradiation. Temperature rise goes along with the formation of both axial and radial cracks. Cracks are not bound to the mineralogical composition but their development is governed by macroscopic temperature gradients and the geometry of the sample. A thermal and a thermomechanical finite element model are formulated and used to calculate temperature distributions and induced thermal stresses. The results indicate that tensile stresses exceed tensile strength leading to cracks as observed experimentally.

► Microwave heating of fine-grained basalt leads to thermal stresses and damage of samples.
► No effects of differential heating and thermal expansion of single grains along the grain boundaries.
► Comparison of experiment and simulation provides a good explanation.