TY  - JOUR
A1  - Burek, Katja
A1  - Dengler, Joachim
A1  - Emmerling, Franziska
A1  - Feldmann, Ines
A1  - Kumke, Michael Uwe
A1  - Stroh, Julia
T1  - Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems
JF  - ChemistryOpen
N2  - The hydration process of Portland cement in a cementitious system is crucial for development of the high‐quality cement‐based construction material. Complementary experiments of X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time‐resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time‐dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium−silicate−hydrates (C−S−H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C−S−H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.
KW  - cement admixtures
KW  - cement hydration
KW  - Europium
KW  - luminescence
KW  - SEM
KW  - X-ray diffraction
Y1  - 2019
U6  - https://doi.org/10.1002/open.201900249
SN  - 2191-1363
VL  - 8
IS  - 12
SP  - 1441
EP  - 1452
PB  - Wiley-VCH-Verl.
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Burek, Katja
A1  - Krause, Felix
A1  - Schwotzer, Matthias
A1  - Nefedov, Alexei
A1  - Süssmuth, Julia
A1  - Haubitz, Toni
A1  - Kumke, Michael Uwe
A1  - Thissen, Peter
T1  - Hydrophobic Properties of Calcium-Silicate Hydrates Doped with Rare-Earth Elements
JF  - ACS sustainable chemistry & engineering
N2  - In this study, the apparent relationship between the transport process and the surface chemistry of the Calcium-Silicate Hydrate (CSH) phases was investigated. For this purpose, a method was developed to synthesize ultrathin CSH phases to be used as a model substrate with the specific modification of their structure by introducing europium (Eu(III)). The structural and chemical changes during this Eu(III)-doping were observed by means of infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and time-resolved laser fluorescence spectroscopy (TRLFS). These alterations of the CSH phases led to significant changes in the surface chemistry and consequently to considerable variations in the interaction with water, as evidenced by measurements of the contact angles on the modified model substrates. Our results provide the basis for a more profound molecular understanding of reactive transport processes in cement-based systems. Furthermore, these results broaden the perspective of improving the stability of cement-based materials, which are subjected to the impact of aggressive aqueous environments through targeted modifications of the CSH phases.
KW  - Rare-earth elements
KW  - Europium
KW  - Luminescence
KW  - Metal-proton exchange reaction
KW  - Contact angle
KW  - Infrared spectroscopy
KW  - X-ray photoelectron spectroscopy
Y1  - 2018
U6  - https://doi.org/10.1021/acssuschemeng.8b03244
SN  - 2168-0485
VL  - 6
IS  - 11
SP  - 14669
EP  - 14678
PB  - American Chemical Society
CY  - Washington
ER  -