Patterns of Desiccation Cracks in Saline Bentonite Layers

Formation of cracks as a result of desiccation is a ubiquitous phenomenon in nature which is influenced by various factors including the environmental conditions, the properties of soil and the evaporating fluid. In this work, a comprehensive series of experiments is conducted to investigate the salinity effects on patterns formation during desiccation of bentonite layers. To do so, mixtures of bentonite and NaCl solutions were prepared with salt concentrations ranging from 3 to 15 %. The mixture was placed in a petri dish mounted on a digital balance to record the evaporation dynamics in an environmental chamber in which the ambient temperature and relative humidity were kept constant. An automatic digital camera was used to record cracking dynamics formed during the desiccation of clay layers. Results illustrated that the salt concentration had significant effects on the initiation, propagation, morphology and general dynamics of cracks. It was found that higher salt concentrations resulted in larger crack lengths due to the effects of NaCl on colloidal interactions among particles as well as the drying behavior. Additionally, using scanning electron microscopy, the influence of salt concentration on the patterns of cracks was investigated at different scales down to a few hundred nanometers. The present results provide new insights into the salinity effects on the cracking patterns and dynamics during desiccation of clay layers.