TY - CONF A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten A1 - Leinitz, Sarah ED - Diouri, A. ED - Boukhari, A. ED - Ait Brahim, L. ED - Bahi, L. ED - N., Khachani ED - Saadi, M ED - Aride, J. ED - Nounah, A. T1 - Concrete casting robustness improvement due to active rheology N2 - With ongoing innovation in process technology, the challenges of concrete technology are more and more focused on the rheological optimisation for these processes, since improper mixture stability or poor compaction ability negatively affect the concrete homogeneity and quality. However, along with the increasing complexity of today’s concrete mixture compositions, concrete becomes more prone to failure regarding the casting process. Variable properties of the raw materials typically cause changing workability. The reasons can be found among others in scattering water contents, physical or chemical properties of the cement or varying environmental temperatures. Robustness in the delicately adjusted rheology, however, is of utmost importance for modern and future process technology, from sprayed concrete over pumpable concrete towards 3D-printing, with regard to the long-term strength, the function and the durability. Typically, material induced changes cannot be identified easily due to the complex interactions of concrete constituents. Therefore, a precise and prompt counteraction is impossible. However, it is known that the yield stress can be controlled by addition of supplementary superplasticizer or stabilising agent. In combination with computerized process observation tools that can rapidly interpret and react on changes in the rheology, it is therefore thinkable, that only these two admixture types can adjust the rheology steadily and permanently, regardless of the actual root cause for observed macroscopic rheology change. The presentation will firstly give a comprehensive overview of effects at the interface between pore solution, particles and hydrates, which affect the rheology of fresh concrete. Secondly, ways are recommended how the rheology can be actively manipulated before eventually computerized methods are demonstrated that help to actively and rapidly assess and counteract performance scatter during steady casting processes. T2 - 2nd International Congress on Materials & Structural Stability (CMSS-2017) CY - Rabat, Morocco DA - 22.11.2017 KW - Cusum KW - Rheology KW - Control Chart KW - Concrete KW - Robustness PY - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-444317 SN - 2261-236X VL - 149 SP - 01001-1 EP - 01001-7 PB - EDP Sciences CY - Les Ulis AN - OPUS4-44431 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Leinitz, Sarah A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten T1 - Assessment of rheological effects in the binder on the rheology of mortar and concrete N2 - In the last years flowable concrete has become increasingly important in applications such as, for systems with highly reinforced concrete with a complicated formwork, or sprayed concrete and 3D-printing of concrete. For all these applications it is necessary to have tailored rheological properties. Rheology can be described by values of yield stress and plastic viscosity, which can be determined for example by evaluation of rheometer measurements. But for different materials various rheometers with different geometries and stirrers are being used. To see the effects from paste in concrete, it is necessary to investigate mixes of paste, mortar and concrete, stepwise. But currently there exists no device, which is calibrated for these different systems at once. Due to this fact, conventional tests such as V-funnel efflux-time and flow diameter were determined, as well as rheometer data in different cell sizes and geometries. In this study the assessment of rheological effects in the binder on the rheology of mortar and concrete was investigated by using combination of two rheometers. T2 - Rheologische Messungen an Baustoffen 2018, 27. Workshop und Kolloquium CY - Regensburg, Germany DA - 07.03.2018 KW - Rheology KW - Cement KW - Mortar KW - Upscaling KW - Superplasticizer PY - 2018 SN - 978-3-7469-1878-5 VL - 27 SP - 109 EP - 111 PB - tredition GmbH AN - OPUS4-44444 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Haist, M. A1 - Link, J. A1 - Nicia, D. A1 - Leinitz, Sarah A1 - Baumert, C. A1 - von Bronk, T. A1 - Cotardo, D. A1 - Eslami Pirharati, M. A1 - Fataei, S. A1 - Garrecht, H. A1 - Gehlen, C. A1 - Hauschildt, I. A1 - Ivanova, I. A1 - Jesinghausen, S. A1 - Klein, C. A1 - Krauss, H.-W. A1 - Lohaus, L. A1 - Lowke, D. A1 - Mazanec, O. A1 - Pawelczyk, S. A1 - Pott, U. A1 - Radebe, N. W. A1 - Riedmiller, J. J. A1 - Schmid, H.-J. A1 - Schmidt, Wolfram A1 - Secrieru, E. A1 - Stephan, D. A1 - Thiedeitz, M. A1 - Wilhelm, M. A1 - Mechtcherine, V. T1 - Interlaboratory study on rheological properties of cement pastes and reference substances: comparability of measurements performed with different rheometers and measurement geometries N2 - 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. KW - Rheometry KW - Rheology KW - Interlaboratory test KW - Test setup KW - Testing procedure KW - Cement paste KW - Ultrasound gel PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-511220 SN - 1871-6873 VL - 53 IS - 4 SP - 92 PB - Rilem AN - OPUS4-51122 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Leinitz, Sarah A1 - Lu, Z. A1 - Becker, S. A1 - Stephan, D. A1 - von Klitzing, R. A1 - Schmidt, Wolfram ED - Mechtcherine, V. ED - Khayat, K. ED - Secrieru, E. T1 - Influence of different accelerators on the rheology and early hydration of cement paste N2 - Special applications like pumping, spraying or printing of concrete require the precise adjustment of very specific rheological properties at different time steps during the casting process. Superplasticizers such as polycarboxylate ethers (PCE) can be used to obtain the required flowability, which, possibly in combination with additional rheology modifying admixtures, generate the required specified consistency. However, after the application, the concrete should change the rheological properties immediately in order to avoid deformations at rest. Therefore, the use of accelerators can be effective. Accelerators influence the hydration of cementitious materials, and thus the rheological properties over the course of time and the setting. In this paper, the influence of different accelerators on the rheology and early hydration of cement paste as well as the interaction of accelerator and PCE are presented. Methods like rheometry, needle penetration tests and practical Tests like spread flow were applied. The used accelerators showed accelerating behavior on the cement pastes without and in the presence of PCE. At the same time an influence on the rheology could be observed. This effect was less in the mixes with PCE, especially at the highest water/cement ratio (w/c). KW - Rheology KW - Cement paste KW - Accelerator KW - Superplasticizer KW - Setting PY - 2019 SN - 978-3-030-22565-0 U6 - https://doi.org/10.1007/978-3-030-22566-7 SN - 2211-0844 VL - 23 SP - 106 EP - 115 PB - Springer ET - 1 AN - OPUS4-49139 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Schmidt, Wolfram A1 - Leinitz, Sarah A1 - Mota, Berta A1 - Crasselt, Claudia ED - Liu, Jiaping ED - Wang, Ziming ED - Holland, Terence ED - Huang, Jing ED - Plank, Johann T1 - Influence of the aqueous phase of cement paste on the rheology in the presence of PCE N2 - The paper presents rheometric results and hydration curves for cementitious systems based on cement mixed with different aqueous phases at solid volume fraction of  = 0.45. The varied aqueous phases were deionized water, limewater, the filter residue of a cement paste mixed at w/c = 2.0, and the filtrate of cement paste at solid volume fraction of 0.45. Each cementitious system provided different amounts and sizes of particles formed in the aqueous phase. The pastes were observed with and without polycarboxylate ether based superplasticizer. It was observed that the presence of particles causes higher PCE saturation dosages to achieve a minimum value, but the minimum value is only affected in the case of large particles. In all cases with and without PCE, the presence of small particles causes increased plastic viscosity. In addition, with decreased number and size of hydrates in the aqueous phase the hydration was retarded, which was specifically pronounced in the presence of PCE KW - Aqueous phase of cement paste KW - Polycarboxylate ether KW - Rheology KW - Yield stress KW - Plastic viscosity KW - Heat of hydration KW - Syngenite KW - Solid volume fraction PY - 2018 SN - 978-1-64195-029-9 SP - SP-329-34, 428 EP - 443 PB - American Concrete Institute CY - Farmington Hill, Michigan AN - OPUS4-47107 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Priebe, Nsesheye Susan A1 - Schmidt, Wolfram A1 - Mota, Berta A1 - Leinitz, Sarah A1 - Kühne, Hans-Carsten A1 - Rogge, Andreas T1 - The effect of superplasticizers on rheology and early hydration kinetics of rice husk ash-blended cementitious systems N2 - Superplasticizers (SPs) have been employed in concrete technology for decades to improve the workability of concrete in its fresh state. The addition of SPs in cement-based systems affects the early properties. Although the interaction of the cement particles with various SPs has been extensively researched, there still exists limited research on the interaction of SPs with supplementary cementitious materials such as rice husk ash (RHA). This paper investigates the rheological properties and early hydration kinetics of RHA-blended systems with three types of SPs, a polycarboxylate ether (PCE) and two lignosulphonates (LS-acc and LS-ret). In rheological properties, the addition of SP causes an initial improvement of workability as the yield stress is significantly reduced. The pastes with PCE and LS-acc show a slight increase of yield stress over time whereas pastes with LS-ret tend to lower the yield stress slightly over time, further improving the workability. Without SP, pastes with RHA show a lower yield stress but an increase in plastic viscosity as cement is further replaced with RHA. The addition of the LS SPs is observed to lower the plastic viscosity but remains constant with further replacement of cement with RHA. This indicates that LS SPs further adsorbs on RHA particles and hydration products produced causing dispersion of the particles within the system. In early hydration kinetics, pastes with PCE retard hydration and the degree of retardation is further increased with LS SPs. In the presence of RHA, the retardation of LS SP systems is significantly reduced. The pastes with PCE show more ettringite in the SEM micrographs, but is observed to be shorter needles. This indicates an initial good workability for PCE. However, C-S-H and CH were observed to be low in quantity, whereby the pastes with LS show more nucleation sites for C-S-H and CH. The ettringite needles in the LS systems were similar in quantity and more elongated in some cases but not abundant as in the PCE systems. KW - Plastic viscosity KW - Cement KW - CO2 reduction KW - Supplementary cementitious materials KW - Rice husk ash KW - Superplasticizers KW - Hydration KW - Rheology KW - Yield stress KW - Slump flow PY - 2017 UR - http://www.sciencedirect.com/science/article/pii/S0950061817310978?via%3Dihub U6 - https://doi.org/10.1016/j.conbuildmat.2017.05.197 SN - 0950-0618 SN - 1879-0526 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. VL - 150 SP - 511 EP - 519 PB - Elsevier Ltd. AN - OPUS4-41036 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -