Abstract
The general behaviour of stiff pastes is discussed in order to select the most suitable form of apparatus for rheological measurements. Two new instruments, each of the concentric cylinder type, which can be applied to different types of stiff paste, are described. The first relies on the use of a narrow annulus to enable absolute calculations to be made, and incorporates a novel method of filling by using a split outer cylinder. It cannot be used satisfactorily with systems showing very rapid shear hardening, for which the second instrument was designed. This instrument enables the shear to be determined at all points across a wide annulus. Measurements show that, for some systems, Bingham's law of plastic flow is obeyed for each value of the shear, the effect of the shear hardening being to give an increasing value to the yield stress, as the amount of shear increases. Two new ideal rheological bodies are suggested and the effect of hydrostatic pressure on the flow properties of materials is discussed.