Browsing by Author "Mechtcherine, Viktor"

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Open Access
Application of super absorbent polymers (SAP) in concrete construction : update of RILEM state-of-the-art report
(2021) Mechtcherine, Viktor; Wyrzykowski, Mateusz; Schröfl, Christof; Snoeck, Didier; Lura, Pietro; De Belie, Nele; Mignon, Arn; Vlierberghe, Sandra van; Klemm, Agnieszka J.; Almeida, Fernando C. R.; Tenório Filho, José Roberto; Boshoff, William Peter; Reinhardt, Hans-Wolf; Igarashi, Shin-Ichi
Superabsorbent polymers (SAP) are a new, promising class of chemical admixtures which offer new possibilities in respect of influencing the properties of cement-based materials in the fresh, hardening, and hardened states. Much research work has been done in the last two decades to set the stage for introducing this truly multipurpose agent into the practice of construction. In particular, three RILEM Technical Committees: 196-ICC, 225-SAP and 260-RSC contributed considerably to the related progress by coordinating and combining the efforts of international experts in the field. The major product of the RILEM TC 225-SAP work was the State-of-the-Art Report published in 2012. This comprehensive document covered all topics relevant to the application of SAP as a concrete admixture. Since then further important progress has been made in understanding the working mechanisms of SAP in concrete and the effects of SAP-addition on various concrete properties. The article at hand presents an update on the state-of-the-art and is the concluding document delivered by the RILEM TC 260-RSC.
Open Access
Benchmark simulations of dense suspensions flow using computational fluid dynamics
(2022) Haustein, Martin A.; Eslami Pirharati, Mahmoud; Fataei, Shirin; Ivanov, Dimitri; Jara Heredia, Daniel; Kijanski, Nadine; Lowke, Dirk; Mechtcherine, Viktor; Rostan, Daniel; Schäfer, Thorsten; Schilde, Carsten; Steeb, Holger; Schwarze, Rüdiger
The modeling of fresh concrete flow is still very challenging. Nevertheless, it is of highest relevance to simulate these industrially important materials with sufficient accuracy. Often, fresh concrete is assumed to show a Bingham-behavior. In numerical simulations, regularization must be used to prevent singularities. Two different regularization models, namely the 1) Bi-viscous, and 2) Bingham-Papanastasiou are investigated. Those models can be applied to complex flows with common simulation methods, such as the Finite Volume Method (FVM), Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Within the scope of this investigation, two common software packages from the field of FVM, namely Ansys Fluent and OpenFOAM, COMSOL Multiphysics (COMSOL) from FEM side, and HOOMD-blue.sph from the field of SPH are used to model a reference experiment and to evaluate the modeling quality. According to the results, a good agreement of data with respect to the velocity profiles for all software packages is achieved, but on the other side there are remarkable difficulties in the viscosity calculation especially in the shear- to plug-flow transition zone. Also, a minor influence of the regularization model on the velocity profile is observed.
Open Access
Interlaboratory study on rheological properties of cement pastes and reference substances : comparability of measurements performed with different rheometers and measurement geometries
(2020) Haist, Michael; Link, Julian; Nicia, David; Leinitz, Sarah; Baumert, Christian; Bronk, Tabea von; 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; Pawelczyk, Sebastian; Pott, Ursula; Radebe, Nonkululeko W.; Riedmiller, Joachim Jürgen; Schmid, Hans-Joachim; Schmidt, Wolfram; Secrieru, Egor; Stephan, Dietmar; Thiedeitz, Mareike; Wilhelm, Manfred; Mechtcherine, Viktor
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.