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Two types of carbon-based materials, i.e., mesoporous carbon and HNO 3 -oxidized carbon nanotubes, with nearly the same specific surface area and abundant in surface oxygen-containing functional groups were selected in order to examine their effect on the hydration of tricalcium silicate (C 3 S), the main portland cement component, in early stages. Different methods, including XPS and TG-MS analyses, electrokinetic potential measurements, as well as determination of adsorption capacity for calcium ions from aqueous solutions, were used to investigate the physicochemical surface properties of the selected carbon-based materials. It was found that the carbon-based materials with high specific surface area and rich in oxygencontaining functional groups on their surfaces have a catalytic effect on early C 3 S hydration. It was observed that the modification of C 3 S paste with the selected materials added in high concentrations (1 wt% and higher) led to an increase in the rate and degree of C 3 S hydration in the early stages. The mechanism of early C 3 S hydration accelerated by carbon-based materials rich in surface functional groups was clarified by the example of the mesoporous carbon. It was found that the oxygen-containing functional groups present on the carbon surface have both an influence on the content of calcium ions in the aqueous phase of the C 3 S paste and an indirect positive effect in relation to the specific surface of C 3 S.

Different approaches, including determination of the surface tension via capillary penetration measurements and characterization of the surface chemical composition by means of X-ray photoelectron spectroscopy (XPS), were applied to reveal the surface properties of various CNT types produced from acetonitrile (CH 3 CN), cyclohexane (C 6 H 12 ) and methane (CH 4 ). Significant differences were found in the polarity of the CNT surfaces depending on the used precursors. The surface tension of the CNTs increases by utilization of carbon sources in the following order: cyclohexane, methane, acetonitrile. Using XPS analysis a comparatively high contents of nitrogen and oxygen atoms were detected on the surface of the CH 3 CN-CNTs. Based on the results of the mass spectrometry, the strong hydrophobic character observed for the C 6 H 12 -CNTs is assumed to originate from polycyclic aromatic hydrocarbons deposited on the nanotubes' surface during synthesis. The investigation of the deposition of silica on the CNTs by a sol-gel method showed that the polar surface of the CH 3 CN-CNTs provided the most favorable condition for the heterogeneous precipitation of silica. In contrast, no precipitation of silica was observed on the hydrophobic C 6 H 12 -CNTs.

Am Beispiel von Kohlenstoffnanopartikeln unterschiedlicher Funktionalität und Gestalt sollen die Möglichkeiten einer umfassenden Oberflächencharakterisierung vorgestellt werden. Im Fokus der analytischen Arbeiten stehen dabei elektrokinetische und Benetzungsmessungen, die durch Röntgenphotoelektronenspektroskopie sowie Gassorptionsmessungen ergänzt wurden. Damit konnte die chemische Funktionalität, die Oberflächenenergie sowie die Topografie der Partikeloberflächen quantitativ beschrieben werden. Die Kenntnis dieser Größen ermöglicht eine gezielte Auswahl von Partikeln als Verstärkungsmaterialien, aber auch als Nukleierungsmittel.