Photocatalytic Pavements

Abstract

Pavements which have been blended, coated, sprayed, etc., with photocatalytic TiO 2 additives have attracted world-wide interest during the past decade-plus period based on their environmentally beneficial abilities to provide reactive (i.e., 'smog-eating pavement' plus 'self-cleaning') and reflective (i.e., 'cool pavement') impacts. The former 'reactive' capabilities notably involve a de-polluting property where TiO 2 irradiation with UV-A spectrum light is able to oxidatively convert a variety of problematic organic and inorganic pollutants within both atmospheric and aqueous runoff zones. This suite of transportation-generated amenable contaminants notably includes NO X residuals which otherwise represent a serious environmental and human-health challenge within high traffic density, inner-urban highway locations with high-density adjacent resident populations. Multiple laboratory-level photo-reactor studies published over the past several decades have demonstrated this photocatalytic NO X -removal capability, while at the same time scientifically exploring and elucidating key relationships between NO X abatement and various environmental factors (e.g., light wavelength and intensity, ambient relative humidity and surface moisture, pavement temperature, surface soiling impacts, etc.). Field monitoring, albeit in more limited fashion, has provided similarly supportive findings at a number of locations involving not only TiO 2 -bearing pavements but also locations paved with blocks, pavers, bricks, etc. which have been sprayed or coated with TiO 2 -enriched admixtures. This chapter, therefore, provides an overview of the related literature covering academic, industrial, patent, and related perspectives and both experimental and full-scale findings. While this existing body of knowledge is substantial, complementary

TiO2-based Photocatalytic Cementitious Composites: Materials, Properties, Influential Parameters, and Assessment Techniques

“…The governing decomposition mechanism involves the generation of radicals due to the irradiation to the photocatalyst substance, and subsequently converting pollutants into harmless compounds [40,75,76]. The accepted reaction mechanism for the photocatalytic conversion of NO x compounds is represented in Equations (1)–(3) [4,42,77,78]. NO 3 − is harmless in small quantities and would be washed away by water droplets [77,79].…”

“…Similarly, purification of SO 2 is as follows [31,42,80]:SO 2 + OH• → HSO 3 ; HSO 3 + SO 2 → SO 3 ; SO 3 + H 2 O → H 2 SO 4 ; HSO 3 + HO• → H 2 SO 4 .…”

“…According to laboratory evaluations, a typical pattern of NO x removal by the photocatalytic paving blocks is represented in Figure 11. Photocatalysts, such as TiO 2 , can be easily implemented in cementitious materials and paints, thereby creating air-purifying surfaces in a broad range of structures and infrastructures including pavement blocks [42,94,95], filters and membranes for indoor/outdoor air purification, and so on [72,75].…”

“…History of photocatalysis cementitious materials [6,41,42]. (Note: PICADA project: European project as Photocatalytic Innovative Coverings Applications for Depollution Assessment.…”