Photocatalytic properties of cement-based plasters and paints, containing mineral pigments

Innovative cement-based pre-mix products, for surface coating of buildings, possessing photocatalytic activity, arouse great interest due to achievable results in terms of reduction of the air pollution and in the maintenance of aesthetics.The photoactivity is induced by the presence of a photocatalyst, titanium dioxide, which can accelerate the oxidation processes of air pollutants, particularly nitrogen oxides (NOx) and volatile organic compounds (VOCs), mainly produced by incomplete combustion of fuel and present in urban environment through the exhaust gases of motor vehicles. The surfaces which are coated with these products acquire a self-cleaning characteristic (maintenance of original colour), just because the decomposition of organic compounds reduces significantly the ability of atmospheric particles to adhere to treated surfaces, thus facilitating their removal and ensuring a more durable colour. These products are particularly suited to be used in highly congested areas (i.e. historical centres of cities, tunnels, roads), where air pollution reaches significant levels.This study describes the photocatalytic performances of a series of pre-mix products, containing mineral pigments. The tested products are based on hydraulic binders (natural hydraulic lime and cement), the pigments are inorganic; a wide range of colors was chosen and base products performances were investigated to provide a wider choice to the designers. After a brief introduction of the principles of the photocatalysis, the results of a wide experimental work are described. Some considerations in terms of methods of curing and natural exposure are also reported.