TY - CHAP A1 - Becker, S. A1 - Lu, Z. A1 - Leinitz, Sarah A1 - Schmidt, Wolfram A1 - Stephan, D. A1 - von Klitzing, R. ED - Mechtcherine, V. ED - Khayat, K. ED - Secrieru, E. T1 - Particle Interactions in Silica Systems in Presence of Superplasticizer N2 - The flowability of cement paste is of great importance in today’s construction industry and is influenced by additives such as superplasticizers (SP). One type of SPs are polycarboxylate ether type SPs. These additives electrostatically bind with the negatively charged carboxylic groups at the backbone to the positively charged clinker phases. To model positively charged clinker phases with adsorbed SP, silicon Wafers are pre-coated with cationic polyethylenimine (PEI) and SP is adsorbed onto the coated surface (Si/PEI/SP). Two different polycarboxylate ether type (PCE) SP are compared – one for ready-mix concrete and one for precast concrete. In this preliminary study the interaction forces between Si/PEI/SP surface and a silica microsphere (colloidal probe) are investigated under mild physico-chemical conditions (pH *6, ion concentration <10−5 M) using Colloidal Probe Atomic Force Microscopy (CP-AFM). The interaction force between the model surfaces is attractive for low concentration of SP. The force changes from attractive to repulsive by increasing amount of SP. The force upon approach reveals a biexponential behavior. The exponential decay at large and short surface separations are attributed to electrostatic and steric interactions, respectively. The steric forces of the SP for ready-mix concrete show a steeper onset than the SP for precast concrete. The quantification of these interaction forces will be compared to rheological measurements of similar systems. Furthermore, the parameters will be changed to better approach the conditions in real systems, i.e. higher pH and ionic strength. This helps to understand how the forces on the nanoscale influence the macroscopic rheology. KW - Interfacial forces KW - Silica beads KW - Superplasticizer KW - AFM 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 - 571 EP - 579 PB - Springer ET - 1 AN - OPUS4-49183 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 - Lu, Z. A1 - Becker, S. A1 - Leinitz, Sarah A1 - von Klitzing, R. A1 - Schmidt, Wolfram A1 - Stephan, D. ED - Mechtcherine, V. ED - Khayat, K. ED - Secrieru, E. T1 - Rheological properties of silica beads in the presence of different polymers and electrolyte N2 - Properties of interstitial liquid phase in cement paste, including the species and concentrations of polymers and ion etc., play an important role for the rheological properties of cementitious materials. In order to better understand their effect, an inert model substance, spherical silica beads (SBs) with defined surface and granulometry were used in the presence of electrolytes (CaCl2) and/or different polymers, including polycarboxylate superplasticizer (PCE) and polyethylene glycol (PEG). It was found the presence of Ca2+ greatly increases the viscosity and yield stress of silica beads paste (SBP), which is proportional to the [Ca2+]. For the effect of PCE, the addition of PCE is beneficial to the flowability of SBP, but a high dosage of PCE leads to a reversal effect. Furthermore, the yield stress firstly increases and then decreases with increasing [Ca2+] under the same dosage of PCE. The addition of PEG always increases the yield stress of SBP, regardless of the ion concentration and the presence or not of PCE. KW - Rheological properties KW - Ions KW - Superplasticizer KW - Silica beads PY - 2019 SN - 978-3-030-22565-0 SN - 978-3-030-22566-7 U6 - https://doi.org/10.1007/978-3-030-22566-7_72 SN - 2211-0844 VL - 23 SP - 619 EP - 627 PB - Springer ET - 1 AN - OPUS4-49185 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 - CHAP A1 - Schmidt, Wolfram A1 - Ramirez Caro, Alejandra A1 - Sojref, Regine A1 - Mota Gassó, Berta ED - Greim, M. ED - Kusterle, W. ED - Teubert, O. T1 - Contribution of the coarse aggregates to rheology - effects of flow coefficient, particle size distribution, and volume fraction N2 - In order to observe the effect of the aggregate phases between 2 mm and 16 mm without overlap with rheological effects induced by the cement hy-dration and without interactions with a threshold fine sand particle size that affects both, paste and aggregates, rheological experiments were conducted on a limestone filler based paste mixed with aggregates up to 16 mm. Vari-ous aggregate fractions were blended and mixed with the replacement paste in different volumetric ratios. The dry aggregates’ flow coefficients were determined and compared to yield stress and plastic viscosity values at different aggregate volume fractions. The results indicated that the flow coefficient is not a suitable parameter to predict the performance of the aggregates in the paste. It was shown that the yield stress of pastes is largely determined by the blend of different aggregate fractions, while the plastic viscosity to large extend depends upon the coars-est aggregate fraction. Based on the results, ideal aggregate composition ranges for minimised yield stress are presented. For the plastic viscosity no such grading curves to achieve minimum values could be found, but high viscosity curves are identified. KW - Rheology KW - Flow Coefficient KW - Particle Size Distribution KW - Volume Fraction KW - Cement KW - Concrete KW - Reference Material KW - Limestone Filler PY - 2018 SN - 978-3-7469-1878-5 SP - 96 EP - 108 PB - tredition GmbH CY - Hamburg AN - OPUS4-44434 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -