Rheology is by definition the science of flow and deformation of matter.
So to describe the workability of fresh cobcrete one sholuld use rheological apptoach. But to be able to use the science of rheology one has to be able to evaluate the rheological properties of the material. This has been a big problem in the science of concrete technology.
Since Powers and Wiler introduced their plastometer in 1941, several attempts have been made to take a more basic approach to the testing of fresh concrete properties. Most of these attempts, however, have only resulted in various types of prototype equipment. Consequently, the most common way of testing fresh concrete properties is still based on various types of empirical test methods, such as the slump method introduced by Abrams in 1918.
It was a great step foreward, therefore, when Tattersall introduced his two-point test apparatus for measuring concrete workability in 1973. Since then, the concrete technology has gradually introduced the use of rheological approach.