Effect of titanium dioxide nanoparticles on early age and long term properties of cementitious materials
Lee, Bo Yeon
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Today, with increasing global awareness and regulation of air pollution, interest in the smog-abating property of photocatalytic materials is increasing. Titanium dioxide (TiO2) is the most well known photocatalytic semiconductor and is often considered as one way of solving pollution by a passive but an effective way, particularly to reduce atmospheric nitrogen oxides (NOx=NO+NO2). This relatively new technology is already being used in some of the countries as a construction material, commercially sold as photocatalytic cement, photocatalytic pavement, self-cleaning tiles, and self-cleaning glass. Prior research has examined the photocatalytic properties of TiO2 itself, as well as TiO2-containing cement-based materials. The majority of this effort has been on characterizing and enhancing the photocatalytic efficiency. However, relatively little research was performed to assess the potential impact of the photocatalytic reaction on the "parent" or "host" material. In this research, the focus is on the effect of photocatalysis on the composition, structure, and properties of cementitious materials, which contain titania nanoparticles at early and late ages. Fundamental examinations on the addition of these chemically non-reactive nanoparticles to cement-based materials are performed. The high surface area of nanoparticles could alter early age properties of cementitious materials, such as setting time, dimensional stability, and hydration rate. Various experimental techniques as well as mathematical modeling were used to examine and explain the early age hydration of cementitious materials when TiO2 nanoparticles are present. Further, the effects of the TiO2 on the long term durability of cement-based materials are investigated to demonstrate their suitability for long-term use in the field. The photocatalytic NOx oxidation efficiency and NOx binding capability of TiO2 containing cementitious materials are experimentally investigated. The durability of TiO2-cement is examined by various techniques on samples that went through extensive photocatalysis and environmental exposures. These investigations have led to tentative conclusions on the use of TiO2 nanoparticles in cementitious materials, and suggest avenues for future study.