Measurement of yield stress for concentrated suspensions using a plate device

Abstract

Slump has often been correlated with the yield stress of concrete as defined by the Bingham model. The discussion is still open as to what the yield stress value actually is and how to measure the yield stress of a suspension in general and for a cementitious material in particular. A plate device is a recent development in the measurement of yield stress of suspensions that allows for testing at shear rates far below most rotational rheometers. This paper presents the plate device and the modifications made so that it can be used with suspensions such as bentonite or titanium dioxide (TiO2) in aqueous solution, as well as high concentration suspensions such as portland cement paste. A systematic analysis of the experimental results is presented with a critical discussion on the potential use of this device. The results indicate that the yield stresses of the suspensions determined by the plate device were generally lower than those determined by the parallel-plate rheometer. It appears that the pattern of stress growth curve and method of yield stress calculation in plate device experiments are affected by the suspension type. © 2009 RILEM.