Experiments Show a Second Length Scale in Weakly Cohered Granular Materials

Abstract

The structure of cohesive frictional materials changes significantly with increasing the amount of binder. When the binder content is low, the binder exists only between the particle contacts (contact bound structure) whereas at higher binder content, the cohesion-less particles float (dispersed) in a matrix of binder. The structure of the material significantly affects the initiation and progression of failure, i.e. the collapse or failure mechanism. In this study, we perform a series of experiments on cohesive frictional material with contact bound structure to investigate its failure mechanism and effect of dimensional scaling. In order to investigate the effect of scaling, two sets of studies are performed, system (specimen) size effect and particle size effect on glass beads-epoxy, sand-epoxy, and sand-cement specimens. For understanding the system size effect, the specimen dimension is varied while keeping the particle size, density and binder content constant. We observe that with increase in the size of specimen, the strength of the material also increases. Similarly, effect of particle size is investigated by varying the particle size and keeping the specimen dimension, density and binder content constant. We observe that with increase in particle size, the strength of specimen reduces. We perform a set of computed tomography study on this contact bound structure to correlate the structure of the specimen with the observed scaling response.