Rheology of concrete: a study case based upon the use of the concrete equivalent mortar

Abstract

A deeper and wider knowledge of the rheology of concrete could be obtained if a variety of absolute rheological parameters were measured. Although a valuable rheological classification can be induced from concrete rheometers, they do not give the same absolute values of the rheological parameters. Moreover, rheological tests with concrete require a large volume of material. The aim of this work is to use the concrete equivalent mortar (CEM) method (Schwartzentruber and Catherine, Mater Struct 33:475–482, 2000) to get concrete rheological information with an absolute rheometer. Additionally some graph tools that resume the results from several rheological tests are suggested for the design of concretes. CEM have been formulated to test concrete formulations with an absolute rheometer. Steady flow measurements of a CEM corresponding to a self-compacting concrete (SCC) clearly reveal characteristic non-linear viscoplastic behavior which it is not shown by conventional tests used to characterize concretes. The thixotropic behavior of a concrete is well-established using three different rheological tests that can be made with an absolute rheometer testing its corresponding CEM. These tests reveal aspects of the strength and kinetics of the micro-structure that are not observable when thixotropy of concrete is semiquantified with conventional methods. Only with a CEM is possible to make oscillatory shear tests. In this way the viscoelastic behavior of the concrete can be characterized. Results of practical interest are so obtained. For example, the necessity of vibration at rest application to the fresh concrete can be established from frequency sweep tests of CEM in the linear viscoelastic region. The correlation between rheological behaviors of a concrete and its corresponding CEM has been supported. Steady flow and thixotropy rheographs of CEM are suggested as tools for an easy and fast determination of adequate formulation for specific applications.