Photocatalytic Air Purifying Pavements in Belgium Where are We

The construction and rehabilitation of roads are more and more linked to the environmental impact of this road. Durability, noise and air quality become more and more important as design criteria. The choice of materials can influence the environmental impact of traffic and road infrastructure. In this respect, photocatalytic concrete constitutes a promising technique to reduce a number of air contaminants such as NOx and VOC’s. Ideally, the photocatalytic material, titanium dioxide, is introduced in the top layer of the concrete pavement for best results. In addition, the combination of TiO2 with cement-based products offers some synergetic advantages, as the reaction products can be adsorbed at the surface and subsequently be washed away by the rain. A first application has been studied by the Belgian Road Research Centre (BRRC) on the side roads of a main entrance axis in Antwerp with the installation of 10.000 m² of photocatalytic concrete paving blocks. Although measurements on site did not give the expected results due to the configuration of the road surface, the laboratory results indicated a good efficiency towards NO and NO2 abatement as well as a good durability of this air cleaning characteristic. Special attention is given to the nitrogen oxides content in the air, since they are for almost 50% caused by the exhaust of traffic and are at the base of smog, secondary ozone and acid rain formation. For now, the translation of laboratory testing towards results in situ remains critical to demonstrate the effectiveness in large scale applications. Moreover, the durability of the air cleaning characteristic with time remains challenging for the application in concrete roads. In this perspective, several new trial applications have been initiated in Belgium in recent years to assess the “real life” behavior. A field site was set up in the Leopold II tunnel of Brussels in the framework of the European Life+ project PhotoPAQ. This major environmental project aims at demonstrating the effectiveness of photocatalytic materials on a realistic scale. To this purpose, photocatalytic materials have been applied on the walls and roof of the tunnel. Furthermore, in 2010 the INTERREG project ECO2PROFIT started in cooperation with the regional development agency POM Antwerp. Here, a photocatalytic concrete with TiO2 in the top layer was applied for the construction of new pavements on industrial zones in Wijnegem and Lier (province of Antwerp). This paper first gives a short overview of the photocatalytic principle applied in concrete, to continue with some main results of the laboratory research recognizing the important parameters that come into play. In addition, some of the methods and results, obtained during the investigation of the existing application in Antwerp (2005) and during the implementation of the new realizations in Wijnegem and Lier, (2010-2012) and in Brussels (2012-2013), will be presented to provide an overview of the current status of understanding of photocatalytic materials and future perspectives.