Exposed Aggregate Areas and Photocatalytic Efficiency of Photocatalytic Aggregate Mortar

By having the potential to remove nitrogen oxide (NOx) air pollutants generated by vehicles and other anthropogenic combustion processes, particularly in urban areas, photocatalytic concrete has attracted significant commercial interests all over the world. In contrast to typical photocatalyst applications in concrete, in which titanium dioxide (TiO2) - the most utilised photocatalyst - is dispersed within the cementitious materials, the study reported here utilises titanium dioxide-coated aggregates. Used in an exposed-aggregate finish, this format aims to have a higher photocatalytic efficiency than titanium dioxide cement-bound materials. An exposed titanium dioxide-coated aggregate has the potential to provide a significantly higher proportion of catalyst to direct ultraviolet radiation and minimise lost performance due to occlusion. The exposed-aggregate surface area on the test mortar samples was measured with three-dimensional imaging techniques. Thereafter, photocatalytic efficiency was measured in comparison with that of the titanium dioxide cement mortar. The relationship between exposed area for photocatalytic reaction and photocatalytic efficiency was established. This indicated that the photonic efficiency increases with increasing exposed area, regardless of the method to support the catalyst - that is, either within the cement paste or externally mounted on the aggregate. The data confirm that exposing coated aggregate significantly enhances photonic efficiency.