Simulation based modelling of time- and shear-dependent disperse and rheological properties of cement suspensions
Final Report Abstract
The aim of the project was to establish a constitutive model to predict the time- and shear-dependent microstructural and rheological properties of cement paste. To fulfil this goal, two experimental designs were developed, a series of experimental investigations were carried out and some numerical simulations were performed. The key scientific achievements within the project are summarised as follows: I. One of the decisive influencing factors that should be taken into account in the microstructural analysis of cementitious materials is the shear history, e.g. pre-shearing intensity. To obtain a more realistic output of the model, the boundary conditions (e.g. pre-shearing) have to be optimised first to achieve the maximum deflocculation state defined as the initial state. Due to the SIPM and sedimentation expected to occur in a wide gap rheometer during the experiments, the pre-shearing using a vane rotor in the rheometer might result in an under- or overestimation of the actual torque value recorded and reported by the rheometer. Thus, a high pre-shearing imposed by the vane rotor is not the optimal scenario to yield the maximum deflocculation. We proposed in our study to use external pre-shearing with a drill, to avoid the effect of SIPM and sedimentation allowing the vane rotor to record the actual value of the torque. A systematic study for determining the level of external pre-shearing was proposed. 1700 rpm over 60 s was the most appropriate pre-shearing intensity to achieve the maximum deflocculation state, as after the interpolation the initial lambda (λ0.2 s) at resting time 0 (exactly after pre-shearing with the drill) is about 0.02, so close to zero. II. Since microstructure is highly linked with shear history, the influence of pre-shearing and the subsequent resting time on rheometer results has to be considered. It was revealed in our work that the microstructure of the investigated cement paste (with the same shear history) increases linearly with resting time up to 10 minutes. Those findings enable a more precise prediction of rheological material behaviour at different shear histories i.e., in different processing steps such as pumping processes in longer distances and additive manufacturing. An increased resting time causes a more pronounced variation of the microstructure and thus the rheological properties of the cement-based material, resulting in potential challenges during pumping or 3D printing processes if this delay is not analysed and included in the calculations. III. Numerical CFD simulations were carried out in this project first to describe accurately the complex flow behaviour of the material in a wide gap vane-in-cup rheometer. Through numerical simulations, non-linear shear rate distributions, as well as the plug region in a wide gap rheometer for cement paste, were studied, investigated and compared with experimental results. As part of the simulation benchmarking in cooperation with other working groups involved in the SPP 2005, the CFD simulations carried out in the project were successfully calibrated and validated as a precondition for the further project work. These simulations enabled us to choose the optimum positions of the FBRM probe (at mid-height of the vane probe and with an angle of 45° between flow direction and the FBRM probe window) to minimize possible artefacts and enhance the accuracy of the results. Moreover, the CFD simulations were crucial for a proper evaluation and interpretation of the differences observed by the FBRM probe measurements at different radial positions. IV. A coupled FBRM-rheometer setup, developed in this work for a wide gap rheometer, enabled us to determine in-situ microstructural variations of cement paste at different shear rates.
Publications
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Numerical Simulation of the Flow Behavior of Newtonian Fluids in a Wide Gap Rheometer by CFD. RILEM Bookseries (c(2019, 8, 25)), 588-595. Springer International Publishing.
Eslami Pirharati, Mahmoud; Ivanov, Dimitri; Krauss, Hans-W.; Schilde, Carsten & Lowke, Dirk
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Synthesis and Analysis of Spherical Cementitious Model Particles. RILEM Bookseries (c(2019, 8, 25)), 602-609. Springer International Publishing.
Ivanov, Dimitri; Becker, Simon; Lu, Zichen; Eslami Pirharati, Mahmoud; Kwade, Arno; Krauss, Hans-W.; Stephan, Dietmar; von Klitzing, Regine & Schilde, Carsten
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Effect of Different Shear Rates on Particle Microstructure of Cementitious Materials in a Wide Gap Vane-in-cup Rheometer. Materials, 13(9), 2035.
Eslami Pirharati, Mahmoud; Krauss, Hans-W.; Schilde, Carsten & Lowke, Dirk
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Interlaboratory study on rheological properties of cement pastes and reference substances: comparability of measurements performed with different rheometers and measurement geometries. Materials and Structures, 53(4).
Haist, Michael; Link, Julian; Nicia, David; Leinitz, Sarah; Baumert, Christian; von Bronk, Tabea; Cotardo, Dario; Eslami Pirharati, Mahmoud; Fataei, Shirin; Garrecht, Harald; Gehlen, Christoph; Hauschildt, Inga; Ivanova, Irina; Jesinghausen, Steffen; Klein, Christopher; Krauss, Hans-W.; Lohaus, Ludger; Lowke, Dirk; Mazanec, Oliver; ... & Mechtcherine, Viktor
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Benchmark Simulations of Dense Suspensions Flow Using Computational Fluid Dynamics. Frontiers in Materials, 9(c(2022, 5, 5)).
Haustein, M. A.; Eslami Pirharati, M.; Fataei, S.; Ivanov, D.; Jara Heredia, D.; Kijanski, N.; Lowke, D.; Mechtcherine, V.; Rostan, D.; Schäfer, T.; Schilde, C.; Steeb, H. & Schwarze, R.
