Effects of substrate on cracking patterns and dynamics in desiccating clay layers
Desiccation cracking is ubiquitous in many materials of practical importance, such as in mud, clay soil, pavement, and concrete, and understanding its dynamics and formation is essential for developing an effective means of its prevention or utilization. We report on a phenomenological investigation aimed at delineating the effect of a coarse-textured substrate on the cracking dynamics and morphology of an overlying kaolinite clay layer. Drying experiments were carried out using a glass container mounted on a digital balance, packed with a thin layer of kaolinite clay overlying seven types of sand that differed in their particle size distributions. An automatic imaging system recorded the dynamics of cracking at the evaporating surface. Dynamic analysis suggests a decreased duration of cracking with increased substrate particle size and substrate-independent initial crack propagation. Analysis of the cracking morphology indicates a decreased crack density and larger crack length, and an increased crack width mean and standard deviation with increased substrate particle size. Scanning electron microscopy results, used to study the extent of cracking over various length scales, indicate that only macroscopic cracks formed on the kaolinite clay surface. Fractal and density correlation function analysis of the final crack networks indicate the dependency of the fractal dimension on the substrate particle size, and a crossover length scale ξ that separates the fractal regime from the uniform crack density regime. For length scales greater than ξ, the density correlation function asymptotically approaches the crack density at the surface of the clay. Key Points Increasing crack density with decreasing substrate particle size Smaller crack length with decreasing substrate particle size Smaller crack width with decreasing substrate particle size © 2014. American Geophysical Union. All Rights Reserved.
cracking patterns and dynamics
kaolinite clay desiccation