Development of an adaptive coaxial concrete rheometer and rheological characterisation of fresh concrete

<jats:title>Abstract</jats:title> <jats:p>The accessibility to rheological parameters for concrete is becoming more and more relevant. This is mainly related to the constantly emerging challenges, such as not only the development of high-strength concretes is progressing very fast but also the simulation of the flow behaviour is of high importance. The main problem, however, is that the rheological characterisation of fresh concrete is not possible via commercial rheometers. The so-called concrete rheometers provide valuable relative values for comparing different concretes, but they cannot measure absolute values. Therefore, we developed an adaptive coaxial concrete rheometer (ACCR) that allows the measurement of fresh concrete with particles up to <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/j_arh-2022-0140_eq_001.png" /> <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msub> <m:mrow> <m:mi>d</m:mi> </m:mrow> <m:mrow> <m:mi mathvariant="normal">max</m:mi> </m:mrow> </m:msub> <m:mo>=</m:mo> <m:mn>5.5</m:mn> <m:mspace width=".5em" /> <m:mi mathvariant="normal">mm</m:mi> </m:math> <jats:tex-math>{d}_{{\rm{\max }}}=5.5\hspace{.5em}{\rm{mm}}</jats:tex-math> </jats:alternatives> </jats:inline-formula>. The comparison of the ACCR with a commercial rheometer showed very good agreement for selected test materials (Newtonian fluid, shear thinning fluid, suspension, and yield stress fluid), so that self-compacting concrete was subsequently measured. Since these measurements showed a very high reproducibility, the rheological properties of the fresh concrete could be determined with high accuracy. The common flow models (Bingham (B), Herschel–Bulkley, modified Bingham (MB) models) were also tested for their applicability, with the Bingham and the modified Bingham model proving to be the best suitable ones.</jats:p>