Sensitivity of kersantite toughness to moisture: influence of the phyllosilicates

Evolution of the fracture behavior of a magmatic rock, the Loperhet kersantite, is under study to have a better understanding of the scaling effect occurring at the surface of monumental stone. A fracture mechanics approach is proposed to measure the ability to withstand a crack initiation and to observe the fracture surfaces after propagation. The influence of water saturation and moisture is considered and dependency of toughness with water vapor pressure is determined during humidification and drying. Results indicate that kersantite toughness decreases when moisture content increases. This is related to clay phases and phyllosilicates, involved in the swelling and identified as the weakness phases of the stone. Indeed, it appears that evolution of toughness and crack paths are related to the mineralogical weathering of these water-sensitive phases. Mineralogical microdamage due to moisture variations is involved in the evolution of the macroscopic mechanical behavior of kersantite.