N. Luongo, S. Massari, S.L. Spagnolo, M.V. Diamanti, B. Daniotti, M.P. Pedeferri
Politecnico di Milano,
Keywords: durability, TiO2 based materials, photocatalysis
Summary:The issue of maintenance is steadily emerging in the framework of the built environment, with a specific focus on durability and service life planning and sustainability evaluations, as the definition of a maintenance plan for building components requires a preventive assessment of durability. Knowing the behavior of materials over time, and consequently of building components, is the optimal way to predict the dynamics of their performance decay. The combination of these concepts with the increasingly development of photoactive materials led to the research field of this work. Anatase phase titanium dioxide TiO2 is the largest used photocatalyst, with increasing applications. Moreover, its contribution to the mixture in the production of mortar allows exploiting its photoactivated depolluting and self-cleaning potential, by means of hydrophilicity. These properties reveal their effects by means of the contribution of solar energy (UV radiation), able to activate the photocatalysis through chemical reactions. This study, indeed, concerns photocatalytic cements, a topic already faced by many researches, which served as basic knowledge of our study. Such study reports data resulting from experimental tests, which investigate the performance of different samples, in terms of appraisal of durability and loss of performance over time, through accelerated ageing tests. Several behaviors have been observed on specimens with different characterizations, in terms of composition and surface finishing. Results achieved constitute a starting point for predicting the service life of buildings components, granting the transfer of information from materials to systems, in this case the cement based building envelope. Information promotes wise planning of maintenance interventions and control of the global costs. The aim of the experimental campaign was to evaluate the durability characteristics and photocatalytic properties of photocatalytic cement samples. Different samples containing TiO2 in the anatase were tested, in order to study the effect of composition and the surface finishing.. Accelerated aging tests were conducted in a climatic chamber (Fig.1) to evaluate the performance decay and physical degradation over time. In each cycle samples were subjected to UV radiation, rain, freeze-thaw and thermal cycles variations. The ageing cycles on samples in the climate chamber are programmed in terms of humidity, temperature, exposition to UV radiation. Additionally, the standard ISO 15686-2 defines the short-term exposure as an iterative process, in the sense that it has to be adapted and repeated until it can be combined with the in-use condition, long term exposure. Samples performance was evaluated after 50, 100, 150 cycle and 200 cycles (Fig.2). All the specimens were fully characterized with particular attention to the photocatalytic properties that were testes in order to evaluate the eventual decay due to aging cycles.