Effect of vane configuration on yield stress measurements of cement pastes

The reliable yield stress (to) measurement of cement pastes requires selection of appropriate vane configuration and thorough understanding of shear stress distribution acting on top, bottom, and sides of the vane. In this project, 11 vanes containing 2-6 blades, height/diameter ratio (HID) varying from 2.4 to 1.5, and various shapes including cylindrical, conical, and coaxial-cylindrical were considered. The data obtained were normalized with respect to the cohesion (C) determined using the direct shear method. Test results have shown that vanes made with gradually reduced HAD and/or having conical shapes led to relatively increased tau(o) values. For given HAD, the use of coaxial-cylindrical vanes resulted in abrupt breakdown of material structure along with the lowest tau(o) responses. The presence of slots is believed to minimize the end effects and strengthen the assumption of shearing taking place within the suspension, which could be advantageous in tau(o) measurements. (C) 2016 Elsevier B.V. All rights reserved.