Evaluation of Environmental Effectiveness of Titanium Dioxide Photocatalyst Coating for Concrete Pavement

Abstract

Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed with air-cleaning agents with a super-hydrophilic photocatalyst such as titanium dioxide (TiO2). Although this technology has the potential to support an environmentally friendly road infrastructure, several design and operational parameters may affect its effectiveness and need to be evaluated. The objective of this study was to evaluate the environmental and mix design parameters that may affect the effectiveness of the environmental performance of TiO2 coating. An experimental program was conducted: the effects of relative humidity level, flow rate of pollutants, and mix design parameters, including contents of TiO2 and aggregate sizes, were investigated. The environmental efficiency of the samples to remove nitrogen oxides from the atmosphere was measured by using a newly developed laboratory setup. Results of the experimental program showed that the mix designs without fines achieved the highest photodegradation rates. In addition, the increase from 3% to 5% TiO2 resulted in little improvement in the nitrogen oxide removal efficiency, which decreased with the increase in the humidity level and the pollutant flow rate.

Influence of environmental factors on removal of oxides of nitrogen by a photocatalytic coating

“…It has been assumed that at higher relative humidity water molecules compete with pollutant molecules for adsorption sites at the material A c c e p t e d M a n u s c r i p t 18 surface, which would explain the decrease in pollutant removal (Hüsken et al, 2009;Laufs et al, 2010;Maggos et al, 2007b;Ao et al, 2003). Dylla et al (Dylla et al, 2010) also observed an increase in removal with higher contact times as observed in this study (Figure 4a). Increasing contact time increases the probability of pollutants coming in contact with the material surface and being adsorbed and reacted, hence the positive contrast for that factor.…”

“…It should be noted, however, that the other studies used higher inlet concentrations (300 ppb and over) than this study (150 ppb). For example, Dylla et al (Dylla et al, 2010) observed NO removals in the 20 to 60% range for contact time varying from 2.4 to 7.1 minutes.…”

“…Removal increases non-linearly with light intensity (Bengtsson and Castellote, 2010;Lim et al, 2000;Ollis et al, 1991), but decreases with increasing relative humidity (Ballari et al, 2011b;Dylla et al, 2010;Hüsken et al, 2009;Laufs et al, 2010). Relative humidity might also influence NOx removal through reactions taking place in water films at the material surface (Saliba et al, 2001;Jenkin et al, 1988;Svensson et al, 1987; , 2002).…”

“…In the past, researchers have studied a wide range of photocatalytic products, from TiO 2 slurries (Bengtsson et al, 2010;Devahasdin et al, 2003;Lim et al, 2000;Ohko et al, 2009), to paints (Maggos et al, 2007a;Laufs et al, 2010), paving stones (Ballari et al, 2011b;Anon;Hüsken et al, 2009) or concrete containing TiO 2 in its cement matrix (Dylla et al, 2010;Dylla et al, 2011;Chen et al, 2009;Beeldens, 2006). In this study, we focused on a TiO 2 -containing stucco coating applied to concrete.…”

Photocatalytic hydrophobic concrete coatings to combat air pollution

“…Furthermore, mechanical properties of concrete are adversely affected by increasing concentrations of TiO 2 [32]. Other laboratory experiments have employed double layer blocks [17] [33], with only the upper layer having the photocatalyst in relatively high proportions. This preparation, requiring two steps, would ultimately result in increased production costs and some technical inconveniences such as blockage of the porous structure in the concrete and delamination of the photoactive facade.…”