The influence of wall slip on yield stress and viscoelastic measurements of cement paste

The influence of wall slip on the shear yield stress and modulus of cement paste was investigated using a rotational rheometer with smooth-walled concentric cylinders and a vane. The results show that the concentric cylinders suffer from slip during yield stress measurements due to the formation of a water-rich layer at the walls of the cylinders. The use of a vane eliminates slip since shearing occurs within the material. Oscillatory tests were conducted to measure the viscoelastic properties of cement paste. The data for the vane and concentric cylinders are in excellent agreement at stresses below the yield point. It is difficult to determine the influence of slip for stress sweep measurements. Frequency sweep data for various materials show the general applicability of the vane method over several decades of modulus. (C) 2001 Elsevier Science Ltd. All rights reserved.