Abstract
The thesis presents a study of frost action in unbound and in cement stabilised colliery shale. Frost susceptibility was assessed using the Road Research Laboratory frost heave test, employing either a cold room or a deep freeze cabinet. Of the 17 unbound, unburnt shales tested, only four samples were classified as frost susceptible whereas 11 of the 12 unbound, burnt shales tested were frost susceptible. This difference in behaviour has been attributed, particularly, to differences in absorption and in the amount and nature of the fine material in each shale. The addition of cement generally reduced the heave, but certain fine-grained shales showed increased heave when so treated. Both effects can be explained in terms of the relative changes in pore size, in permeability and in tensile strength which result from cement stabilisation. Measurements of the pressures generated when heave was restrained were also undertaken. For the unbound, unburnt shales heave was related to heaving pressure and with the cement stabilised shales significant heave occurs only when the heaving pressure exceeds the tensile strength of the material. Thus, although this approach provided data which assists in building-up a mechanistic picture of frost action, it does not provide a basis for directly predicting frost susceptibility. However, it is suggested that the criteria for assessing the frost susceptibility of cement stabilised materials should be based on dimensional changes and on tensile strength. Frost action, in both unbound and cement stabilised shale, is explained in terms of an energy balance between the work done in heaving and the energy liberated by supercooled freezing, this concept being related to changes in the nature and properties of the various materials.