Photocatalytic degradation ability of cementitious materials: A modeling approach

Concrete technology is a subject of continuous development and improvement. One of the very recent contributions to durability and sustainability of concrete is the self-cleaning ability. This effect can be achieved by applying photocatalytic materials to the concrete mix. In earlier work a test setup was developed for the quantitative assessment of the airpurifying ability of paving stones [1]. Using this setup and the involved test procedure it is now possible to compare the performance of different active cementitious substrates. Furthermore, with the help of this innovative setup, the influences on the degradation efficiency are studied and a basic reaction model is derived. This model follows the Langmuir-Hinshelwood kinetics and is in good agreement with the measurement results obtained. By means of this model an adsorption equilibrium constant as well as a reaction rate constant are derived. These two general measures are sufficient for a comprehensive description of the photocatalytic performance of the system. It will be shown that these measures include the kinetics of the system being the reactor dimensions, residence time, volumetric flow and pollutant concentration. In addition, the inclusion of the two most important external influences, the UV-irradiance and relative humidity, is discussed. Based on the measurements of their influences on the photocatalytic performance, a modification of the total reaction rate calculation is proposed.