@article{21949, abstract = {{This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries. The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.}}, author = {{Haist, Michael and Link, Julian and Nicia, David and Leinitz, Sarah and Baumert, Christian and von Bronk, Tabea and Cotardo, Dario and Eslami Pirharati, Mahmoud and Fataei, Shirin and Garrecht, Harald and Gehlen, Christoph and Hauschildt, Inga and Ivanova, Irina and Jesinghausen, Steffen and Klein, Christopher and Krauss, Hans-W. and Lohaus, Ludger and Lowke, Dirk and Mazanec, Oliver and Pawelczyk, Sebastian and Pott, Ursula and Radebe, Nonkululeko W. and Riedmiller, Joachim Jürgen and Schmid, Hans-Joachim and Schmidt, Wolfram and Secrieru, Egor and Stephan, Dietmar and Thiedeitz, Mareike and Wilhelm, Manfred and Mechtcherine, Viktor}}, issn = {{1359-5997}}, journal = {{Materials and Structures}}, keywords = {{Rheology, Wall Slip, Slip, apparent slip, suspension, cement, concrete}}, title = {{{Interlaboratory study on rheological properties of cement pastes and reference substances: comparability of measurements performed with different rheometers and measurement geometries}}}, doi = {{10.1617/s11527-020-01477-w}}, year = {{2020}}, } @article{21948, abstract = {{Since suspensions (e.g., in food, cement, or cosmetics industries) tend to show wall slip, the application of structured measuring surfaces in rheometers is widespread. Usually, for parallel-plate geometries, the tip-to-tip distance is used for calculation of absolute rheological values, which implies that there is no flow behind this distance. However, several studies show that this is not true. Therefore, the measuring gap needs to be corrected by adding the effective gap extension δ to the prescribed gap height H in order to obtain absolute rheological properties. In this paper, we determine the effective gap extension δ for different structures and fluids (Newtonian, shear thinning, and model suspensions that can be adjusted to the behavior of real fluids) and compare the corrected values to reference data. We observe that for Newtonian fluids a gap- and material-independent correction function can be derived for every measuring system, which is also applicable to suspensions, but not to shear thinning fluids. Since this relation appears to be mainly dependent on the characteristics of flow behaviour, we show that the calibration of structured measuring systems is possible with Newtonian fluids and then can be transferred to suspensions up to a certain particle content.}}, author = {{Pawelczyk, Sebastian and Kniepkamp, Marieluise and Jesinghausen, Steffen and Schmid, Hans-Joachim}}, issn = {{1996-1944}}, journal = {{Materials}}, keywords = {{wall slip prevention, effective gap height, parallel-plate system, structured surfaces, model suspensions, cement paste, fresh concrete}}, title = {{{Absolute Rheological Measurements of Model Suspensions: Influence and Correction of Wall Slip Prevention Measures}}}, doi = {{10.3390/ma13020467}}, year = {{2020}}, } @article{21947, abstract = {{Wall slip is a long-known phenomenon in the field of rheology. Nevertheless, the origin and the evolution are not completely clear yet. Regarding suspensions, the effect becomes even more complicated, because different mechanisms like pure slip or slip due to particle migration have to be taken into account. Furthermore, suspensions themselves show many flow anomalies and the isolation of slip is complicated. In order to develop working physical models, further insight is necessary. In this work, we measured experimentally the wall slip velocities of different highly filled suspensions in a rectangular slit die directly with respect to the particle concentration and the particle size. The slip velocities were obtained using a particle image velocimetry (PIV) system. The suspensions consisting of a castor oil–cinnamon oil blend and PMMA particles were matched in terms of refractive indexes to appear transparent. Hereby, possible optical path lengths larger than 15 mm were achieved. The slip velocities were found to be in a quadratic relation to the wall shear stress. Furthermore, the overall flow rate as well as the particle concentration has a direct influence on the slip. Concerning the shear stress, there seem to be two regions of slip with different physical characteristics. Furthermore, we estimated the slip layer thickness directly from the velocity profiles and propose a new interpretation. The PIV technique is used to investigate the viscosity and implicit the concentration profile in the slit die. It is shown that the particle migration process is quite fast.}}, author = {{Jesinghausen, Steffen and Weiffen, Rene and Schmid, Hans-Joachim}}, issn = {{0723-4864}}, journal = {{Experiments in Fluids}}, keywords = {{Rheology, Wall Slip, Slip, apparent slip, suspension}}, title = {{{Direct measurement of wall slip and slip layer thickness of non-Brownian hard-sphere suspensions in rectangular channel flows}}}, doi = {{10.1007/s00348-016-2241-6}}, year = {{2016}}, }