Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-49378 Beitrag zu einem Tagungsband Ramirez Caro, Alejandra; Pauli, Jutta; Mota, Berta; Crasselt, Claudia; Artemeva, Elena; Schmidt, Wolfram; Resch-Genger, Ute A Spectroscopic Study of the Superplasticizer Effect on Early Cement Hydration Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products. 2018 The Sixth International Symposium on Nanotechnology in Construction (NICOM6) Hong Kong, China 02.12.2018 05.12.2018 1 9 2019-10-28 OPUS4-46277 Beitrag zu einem Tagungsband Ramirez Caro, Alejandra; Mota, Berta; Artemeva, E.; Pauli, Jutta; Schmidt, Wolfram; Resch-Genger, Ute A spectroscopic study of the superplasticizer effect on early cement hydration Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products. Weimar F.A. Finger-Institut für Baustoffkunde 2018 Tagungsband der 20. Internationalen Baustofftagung ibausil 20 978-3-00-059950-7 20. Internationale Baustofftagung Weimar, Germany 12.09.2018 14.09.2018 1 6 2018-10-24 OPUS4-50952 Zeitschriftenartikel Ramirez Caro, Alejandra; Pauli, Jutta; Mota, Berta; Simon, Sebastian; Schmidt, Wolfram; Resch-Genger, Ute C⁠3A passivation with gypsum and hemihydrate monitored by optical spectroscopy Tricalcium aluminate (C⁠3A) is found with less than 10% wt. of the total composition; however, during hydration, C⁠3A plays an important role in the early hydration of cement in the presence of gypsum as a set retarder. The aim of this investigation is to assess the suitability of optical spectroscopy and a dye-based optical probe to monitor early hydration of C⁠3A in the presence of gypsum and hemihydrate. Optical evaluation was performed using steady-state fluorescence and diffuses reflectance spectroscopy (UV-VisDR). Phase characterization during hydration was done with in-situ X-ray diffraction. UV-VisDR with a cyanine dye probe was used to monitor the formation of metastable phases and was employed together with fluorescence spectroscopy, to follow the Aggregation and disaggregation of the dye during hydration. In conclusion, for the first time, a cyanine dye was identified as a feasible and stable probe to monitor C⁠3A hydration changes in the presence of calcium sulfate. Amsterdam Elsevier Ltd. 2020 Cement and Concrete Research 133 106082 10.1016/j.cemconres.2020.106082 2020-07-15 OPUS4-36862 Beitrag zu einem Tagungsband Schmidt, Wolfram; Mota Gassó, Berta; Sturm, Heinz; Pauli, Jutta Greim, M.; Kusterle, W.; Teubert, O. Influence of effects on nano and micro scale on the rheological performance of cement paste, mortar and concrete Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as self-compacting concrete. Today, admixture addition has become common practice in concrete technology, but the understanding of their highly complex mode of operation is extremely difficult and demands for understanding of processes within the range between nanometres and centimetres. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The present study discusses fundamental mechanisms at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation, and links these effects to macroscopic flow phenomena. Methods are discussed that appear promising interdisciplinary tools for enhancement of the understanding of the relevant interactions that are responsible for the macroscopic flow of flowable concrete. Hamburg tredition 2016 Rheologische Messungen an Baustoffen 978-3-7345-1313-8 25. Workshop und Kolloquium Rheologische Messsungen an Baustoffen Regensburg, Germany 02.03.2016 03.03.2016 294 307 2016-07-15 OPUS4-38849 Beitrag zu einem Tagungsband Mota Gassó, Berta; Schmidt, Wolfram; Pauli, Jutta; Sturm, Heinz Influences of hydration effects on the flow phenomena of concrete with admixtures Today, chemical admixtures like superplasticisers and stabilising agents are extremely important for modern concrete technology. These agents have meanwhile become common practice in concrete technology, but the understanding within the entire system lags far behind their application. The macroscopic rheology of concrete in the presence of superplasticizers strongly depends upon effects on a much smaller scale such as the hydration of the cement, the adsorption of superplasticizers, and the pore solution chemistry. Frankfurt am Main Gesellschaft Deutscher Chemiker e.V. 2016 GDCh-Monograph 50 978-3-936028-96-6 2nd International Conference on the Chemistry of Construction Materials München, Germany 10.10.2016 12.10.2016 276 279 2017-01-04 OPUS4-36882 Beitrag zu einem Tagungsband Schmidt, Wolfram; Weba, Luciana; Silbernagl, Dorothee; Mota Gassó, Berta; Höhne, Patrick; Sturm, Heinz; Pauli, Jutta; Resch-Genger, Ute; Steinborn, Gabriele Khayat, Kamal Henry Influences of nano effects on the flow phenomena of self-compacting concrete Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as selfcompacting concrete. Meanwhile admixtures have become common practice in concrete technology, but the understanding of these highly complex polymers in the entire concrete system lags far behind their application. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The present study discusses fundamental mechanisms at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation, and links these effects to macroscopic flow phenomena. Methods are discussed that appear promising interdisciplinary tools for enhancement of the understanding of the relevant interactions that are responsible for the macroscopic flow of flowable concrete. 2016 Flowing toward Sustainability 8th International RILEM Symposium on Self-Compacting Concrete Washington, D.C., USA 15.05.2016 18.05.2016 245 254 2016-07-18 OPUS4-38881 Beitrag zu einem Tagungsband Ramirez Caro, Alejandra; Pauli, Jutta; Schmidt, Wolfram; Resch-Genger, Ute Study of the superplasticizer-cement hydration interaction by optical spectroscopy Nowadays, superplasticizers (SPs) are widely used to increase fluidity and reduce water content in concrete; thus, allowing better workability for final applications. The present study will focus on the hydration effect using comb shape polycarboxylates (PCEs), which are known to allow a very low water/cement ratio (w/c of 0.20) or less.Optical methods have been successfully used for the analysis and monitoring of the interactions between a broad variety of nanoscale and molecular systems like nanoparticles of various chemical composition and different types of organic ligands or biomolecules.This encouraged us to assess the potential of these methods, and particularly fluorescence, for the investigation of the interactions that occur at the interface between hydrate surfaces of cement particles and PCE at a very early stage of concrete formation and to differentiate between the impact of PCE's molecular structures on such interactions. Frankfurth am Main Gesellschaft Deutscher Chemiker e.V. 2016 GDCh-Monograph 50 978-3-936028-96-6 2nd International Conference on the Chemistry of Construction Materials Munich, Germany 10.10.2016 12.10.2016 260 263 2017-01-04