MECHANISM OF BREAKDOWN OF LIMESTONE NODULES IN A FREEZE-THAW ENVIRONMENT

When exposed to a freeze-thaw environment, water soaked limestone nodules show two types of disintegration. In the first type the nodule fractures into a few, comparatively large pieces and in the second the surface of the nodules becomes pitted. The causes of these breakdowns have been investigated. It appears that the most probable cause of the fracture is the development of a hydrostatic pressure in the unfrozen part of the original water content as it becomes encased by initial ice formation. For breakdown to occur the hydrostatic pressure has to overcome the tensile strength of the ice-limestone composite. The required pressure can only be generated if the nodule contained a critical volume of water at the beginning of freezing. This mechanism suggests, that for a fully saturated limestone nodule, there is a critical size, determined by its porosity, below which the nodule will not be broken. This mechanism also suggests that for bulk water there is a critical volume below which no fracturing will occur when frozen. The existence of this critical volume of water has been experimentally demonstrated. © 1979.