Frank Dehn

Photocatalytic activity of semiconductor-modified cement. Influence of semiconductor type and cement ageing

Abstract Photocatalyst-modified cements are discussed for various applications in building and environmental technology ranging from self-cleaning surfaces to solar-powered remediation devices for polluted waters. In this work, the photocatalytic atrazine degradation by white Portland cement samples modified with different semiconducting oxides (TiO 2 in form of Degussa P25, Hombikat UV 100, coarse-grained anatase, and ZnO) was used as a model reaction to investigate a possible application of modified cements for the degradation of pollutants on building surfaces. The cement mixtures were also characterised with respect to hydration kinetics and compressive strength which are relevant for possible construction applications. Particle suspensions containing 1xa0μg/l atrazine were irradiated with a sun simulator, and the atrazine degradation was monitored by ELISA (enzyme-linked immunosorbent assay). The atrazine degradation followed first-order kinetic and the obtained rate coefficients were compared with the degradation rate by unmodified cement samples. A significant enhancement of the photocatalytic activity due to the addition of 10xa0wt.% TiO 2 in the form of Degussa P25 and Hombikat UV 100 to Portland cement was observed, whereas addition of ZnO and coarse-grained anatase showed no effect. The primary crystal particle size of the semiconductor seems to have a significant influence on the photocatalytic efficiency of the semiconductor-modified cement samples. Additionally, modified cements were subjected to defined ageing conditions and carbonation was followed directly by laser Raman spectroscopy. Photocatalytic activity decreases during ageing of the hardened cement pastes. However, aged cement modified with Degussa P25 or Hombikat UV 100 exhibited at least threefold degradation efficiency compared to unmodified cement. Taking into account the sufficient radiation over a long time in the environment, degradation of harmful substances by modified cement samples could contribute considerably to the abiotic degradation of pollutants in the environment.

Experimental Investigation on Ultra High-Strength Concrete under Concentrated Loading

This report presents the results of an experimental program dealing with ultra high strength concrete (UHSC) under concentrated load. The implemented tests should be used for the determination of the bearing capacity under concentrated load and for the observation of the failure behavior, Specimens made of plain and reinforced concrete were tested, whereby a helical reinforcement was used. The results were compared with an extrapolation of existing design rules established for normal and high strength concrete. In this context, two different UHSC and one high strength concrete for comparison were investigated in order to recognize the influence of load. The results showed that the bearable concentrated load depends on the compressive strength and also on the concrete composition. Furthermore the under-proportional increase of the tensile strength in relation to the compressive strength has an important influence on the bearing behavior of UHSC.