Mechanical Rock Disintegration by Frost and Salt Crystallization

Authors: Angélique Prick, Université de Liège

Original Language: French

Abstract

This work constitutes a contribution to the study of alteration by the action of water, salts and frost on soft French Mesozoic limestones. Alteration is evaluated by the dilatometric method and measurements of dynamic elastic modulus. The dilatometric behavior of samples subjected to 30 wetting/drying cycles shows the establishment of a hydric equilibrium in the porous medium, accompanied by water migrations whose characteristics depend on thermal and hydric conditions in various parts of the core. This induces anisotropic contraction in some samples. Samples subjected to calcium sulfate crystallization showed a residual length increase significantly greater than the dilatometric response of samples of the same lithology subjected to cycles in distilled water. Gypsum forms surface crusts on limestones, inducing impermeabilization of their surface and limiting subsequent water uptake and hydraulic dilations. Hydration of existing sodium sulfate crystals does not cause significant residual length increase: some sodium sulfate crystals formed in the porous medium are dissolved by subsequent humidifications in distilled water. Certain porosimetric characteristics can be correlated with the haloclastic response. The altering processes occurring during freezing of a wet sample are not only the volumetric expansion accompanying the transformation of water to ice but also cryosuction, which caused significant sample contractions linked to the migration of unfrozen water toward existing ice crystals. Factors influencing the dilatometric response to freezing are the degree of saturation of the rock (above or below a critical degree of saturation), lithology (migrations are best developed in rocks with multimodal porosity) and cooling rate.