Titanium dioxide (TiO2) has a photocatalytic effect and thus contributes to degrade air pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOC). Precondition is a sufficient incidence of light on the photocatalyst. Titanium dioxide added to the concrete mixture leads to concrete- and paving stones with a photocatalytic effect.
The medium-sized enterprise FC Nüdling Betonelemente GmbH & Co. KG (Fulda) has produced stone models which vary in surface, colour, composition, manufacturing process, type of cement and TiO2-forms, in order to develop a paving with an optimized degradation of nitrogen oxides. The effectiveness was then measured by the Fraunhofer Institute for Molecular Biology and Applied Ecology. A lab, Canyon test areas and the Gothaer Platz in Erfurt served as testgrounds. Compared to conventional surfaces, a reduction capacity of 20-35% (at three meters above the pavement) could be verified.
Long-term studies showed that after two years the initial degradation rate for nitrogen oxides still exists. By means of sunlight radiation the nitrogen oxides form nitrate on the stone surface. An environmental risk assessment has shown that the nitrate levels are significantly below the permissible limits.
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