Crack formation in clayey geomaterials subjected to tensile (total) stress

Clay geomaterials are found in natural deposits, man-made earth structures and are used in ceramic industry to manufacture sanitaryware. A major problem encountered in clay geomaterials is crack formation associated with interaction with the atmosphere (evaporation). In the ceramic industry, clayey 'green' geomaterials are subjected to air-drying at ambient temperature before firing. The airdrying generates cracks in the green body that are often not visible at the end of air-drying process, but emerge after the ware is fired. These sanitaryware pieces are discarded with production loss quantified at 10%. A method of testing clayey geomaterials has been developed and used to investigate the response of unsaturated samples subjected to load controlled tensile stresses to the onset of cracking and subsequent failure. Tests were conducted using samples of reconstituted clays prepared using ceramic industry slip casting techniques to allow for creation of identical samples. Samples tested were air dried to a range of differing moisture contents by preserving saturated conditions. Results are interpreted to assess whether cracking occurs when a state of effective stress meets a limiting condition in shear.