Junction formation during desiccation cracking

Abstract

In order to provide a sound physical basis for the understanding of the formation of desiccation crack networks, an experimental study is presented addressing junction formation. Focusing on junctions, basic features of the network determining the final pattern, provides an elemental approach and imparts conceptual clarity to the rather complicated problem of the evolution of crack patterns. Using coffee-water mixtures a clear distinction between junction formation during nucleation and propagation is achieved. It is shown that for the same drying suspension, one can switch from the well-known symmetric triple junctions that are unique to the nucleation phase to propagation junctions that are purely dictated by the variations of the stress state. In the latter case, one can even manipulate the path of a propagating crack in a deterministic fashion by changing the stress state within the suspension. Clear microscopic evidence is provided for the formation of propagation junctions, and material inhomogeneity is observed to be reflected by a broad distribution of angles, in stark contrast to shrinkage cracks in homogeneous solid films.

Characterization of spatial networklike patterns from junction geometry

“…This kind of pattern formation has been extensively observed and reproduced in controlled settings on a variety of materials, including mud, ceramics and coffee grounds. The final patterns result from the combination of two distinct processes: the nucleation of new fractures and the propagation of already existing ones [45][46][47]. Nucleation of new fractures usually involves the formation of tripartite junctions with equal angles of about 120 degrees [47].…”

“…The final patterns result from the combination of two distinct processes: the nucleation of new fractures and the propagation of already existing ones [45][46][47]. Nucleation of new fractures usually involves the formation of tripartite junctions with equal angles of about 120 degrees [47]. Conversely, junctions formed by propagating fractures are the result of either two fractures meeting at a point (usually with an orthogonal angle), or of the branching of one growing fracture (in this latter case the angles formed at the junction are less predictable).…”

Size and boundary effects on desiccation cracking in hardened cement paste

“…A fundamental understanding of desiccation cracking in cementitious materials will help to diminish its occurrence in concrete by choosing the right material composition, pavement dimensions, joint spacing or restraint boundary conditions. Desiccation cracking has been experimentally studied in a wide range of materials such as clay mixtures (Corte and Higashi 1964;Colina and Acker 2000); laponite (Mal et al 2007); coffee-water mixtures (Groisman and Kaplan 1994;Toga and Erdem Alaca 2006); gels (Bohn et al 2005a); starch-water mixtures (Bohn et al 2005b); and alumina suspensions (e.g., Shorlin et al 2000). Desiccation crack-patterns in these experimental systems look very similar to those observed in hardened cement paste, but the reason for crack formation differs.…”

“…The layer thickness effect can be easily explained from linear elastic theory and a critical stress condition (Kitsunezaki 1999). Layer thickness also has an effect on the crack-junction angles (Groisman and Kaplan 1994;Leung and Néda 2000;Toga and Erdem Alaca 2006). An effect of lateral specimen dimensions (width or length) at constant thickness is perhaps not expected.…”

Sculpting of Rocks by Reactive Fluids

“…7.6b) similar to that observed during contraction of ceramic glazing or during drying of paint. Such patterns, dominated by T junctions and 4 sided domains, are largely controlled by the propagation of fractures, rather than by frequent nucleation of new ones, which tend to produce fracture junctions with 60 degree angles (Toga and Alaca, 2006).…”