**4. Pilot Project in Antwerp**

An important issue is the conversion of the results obtained in the laboratory to real applications. In order to see the influence of photocatalytic pavements in "real conditions", a first pilot section of 10.000 m² of photocatalytic pavement blocks was constructed in 2004–2005 on the parking lanes of a main axe in Antwerp [2]. Figure 5 depicts a view of the parking lane, where the photocatalytic concrete pavement blocks have been applied. Only the wearing layer (upper 5–6 mm) of the blocks contains anatase TiO2 mixed in the mass of the concrete layer. The exact composition could not be given by the manufacturer (Marlux, Tessenderlo, Belgium) at that time in view of confidentiality. In spite of the fact that the surface applied on the Leien of Antwerp is quite important, one has to notice the relatively small width of the photocatalytic parking lanes in comparison with the total street: 2 × 4.5 m *versus* a total width of 60 m.

**Figure 5.** Separate parking lanes at the Leien of Antwerp with photocatalytic pavement blocks.

In order to check the durability of the photocatalytic efficiency, pavement blocks were taken from the lane after different periods of exposure and measured in the laboratory with and without washing of the surface. Some of the results are presented in Figure 6. They indicate a good durability of the efficiency towards NO*x* abatement. The deposition of pollutants on the surface leads to a decrease in efficiency which can be regained after washing. Recently repeated measurements in 2010 indicate that even after more than five years of service life, the photocatalytic efficiency of the pavers is still present [22].

Besides the tests in the lab, on site measurements were also carried out. Since no reference measurements without photocatalytic material (prior to the application) exist, the interpretation of these results is rather difficult. Especially the influence of traffic, wind speed, light intensity and relative humidity are playing an important role. Detailed results can be found in [2]. In brief, the field measurements suggested a decrease in NO*x* concentration at the sites with photocatalytic materials, where a levelling out of the pollution peaks is visible. In any case, precaution has to be taken with the interpretation of data since these results are momentary and limited over time. However, at least, they gave an indication of the efficiency of the photocatalytic pavement materials *in situ*, and a basis to work on for future applications.

**Figure 6.** NO*x* reduction measured on two pavement blocks, before (hatched) and after (colored) washing the surface, taken on different locations (house nr. 30, 35, 37, 42, 48, 53) and at different times at the Amerikalei in Antwerp.
