L-box—A tool for measuring the “yield stress”: A theoretical study

Abstract

Yield-stress fluids can form non-flat arrested profiles when they disembogue under the effect of gravity. Relying on this behavior, L-box tests have been used to retrieve fluid properties, specifically yield stress of Self-Consolidating Concrete (SCC) and cement paste. In this study, we aim to find a correlation between the final shape of the sample and the value of yield stress, using theoretical approaches. First, the Cauchy equation for yield-stress fluids is solved asymptotically, and an analytical expression for yield stress is presented. Then, to validate our assumptions in the first approach, the method of characteristics of perfect plasticity is investigated. We show that if the flow is inertialess, the viscosity of the sample does not affect the final shape considerably. We also investigate, in detail, the cases where the sample is not exactly a “simple” yield-stress fluid, i.e., exhibits slightly thixotropic behavior such as SCC and cement paste.