Studying the flow of fresh concrete is influenced by time dependency of the rheological properties of the concrete. This time dependency can be divided into two parts : the non-reversible part, being loss of workability and the reversible part, called thixotropy. Loss of workability can be neglected in some cases, when comparing with the effect of thixotropy, but it is advised to keep track of it, especially in case of SCC for precast industry.
Several attempts have been made to characterize the thixotropic properties of concrete, but no general test procedure is known at this moment to universally describe thixotropy. In most cases, the study of the thixotropic properties is restricted to the area of interest of the authors, mostly the variation of static yield stress. Only one theory takes into account the influence of thixotropy on both viscosity and yield stress : the Hattori-Izumi theory, modified by J.E. Wallevik. This theory will be used to provide a qualitative description of the observed phenomena occurring during pumping of SCC, but due to the large complexity of both the theory and the practical application, a quantitative approach is beyond the scope of this study
