Photocatalytic asphalt mixtures: Mechanical performance and impacts of traffic and weathering abrasion on photocatalytic efficiency

Abstract

The photocatalytic asphalt mixture provides safer roads and mitigates the air quality problems, trapping and degrading organic compounds and also harmful gases. In this research, an asphalt mixture was functionalized with nano-TiO 2 by bulk incorporation, using the contents 3 and 6%, and by spraying coating using an aqueous solution over its surface at different temperatures and rates. For bulk incorporation, the mechanical performance was assessed. The factorsapplication procedure, influence of temperature, spraying rate, incorporation percentage and TiO 2 immobilization (from traffic and rain removal)were evaluated based on Rhodamine B (RhB) degradation. For bulk incorporation, the best content nano-TiO 2 was 3%. The temperature of the substrate has no influence on the photocatalytic results. The most effective spraying rates were 8 and 16 mL/cm 2 . Before simulating the traffic effect, the spraying coating technique was more effective than the bulk incorporation one. After this process, the opposite behaviour was detected. The rain simulation did not cause removal of the nanoparticles. Additionally, the exposed aggregates affected the photocatalytic efficiency, being important their contribution combined to the effect of nano-TiO 2 . To have the maximum benefit of the techniques studied, the ideal solution would be the combination of both, with negligible impact on mechanical performance. NO O NO 2 3(3)O 2 and OH − species required in the above equations are abundantly available in the atmosphere. Consequently, the immobilization of photocatalysts over different external surfaces of the built environment, such as pavements, roofs, tiles, glass, among others, which are subjected to weather (humidity, rain and sunlight), represent a good strategy to sustainably mitigate air pollution. In particular,

Smart, Photocatalytic and Self-Cleaning Asphalt Mixtures: A Literature Review

“…In order to evaluate the photocatalytic ability, the literature presents gas degradation tests, such as NO x and VOCs, most of them according to the standards ISO 22197-1 and JIS TR Z 0018 [60,67,70], and tests of photocatalytic efficiency via the degradation of different organic dyes, such as methylene orange (MO) [61], methylene blue (MB) [6,67] and rhodamine B (RhB) [7,8], which use spectrophotometric techniques (Figure 4). Both tests can be used to evaluate the photocatalytic gas degradation, considering both air depollution and dye degradation for self-cleaning applications.…”

“…In order to avoid or even eliminate the side effect of exposed aggregates, the side and bottom faces of the samples should be coated with bitumen, thus only showing their upper face that is the traditional condition. If this procedure is not performed, this must be considered for the results, that is, photocatalytic efficiency for the blank samples [8].…”

“…For the calculation of photocatalytic efficiency, the decrease of the maximum absorbance (wavelength equals to 662 nm) is observed. Using the Beer-Lambert law In these tests, the source light used to promote the samples irradiation may be only the UV light (shorter wavelengths of about 300 nm) [6] or simulation of sunlight spectra [7,8] and also visible light (for example, by using a halogen lamp with a wavelength of 400-800 nm or light-emitting diodes (LEDs) in different wavelengths) [45,67,85]. The first option, that is, the use of UV light irradiation takes into account only the photocatalytic process activated in this region of the electromagnetic spectrum.…”

“…Several research studies achieved good and promising results related to the degradation of different pollutants emitted by fossil fuels used by road vehicles. Due to the huge surface area of photocatalytic road pavements and its vicinity to the exhaust gases from automobiles, they are quoted as promising surfaces for the reduction (in the presence of sunlight and moisture/O 2 ) of SO 2 , NO x , CO x , HC, soot fouling and other volatile organic compounds (VOCs) present in the atmosphere [6][7][8][9][10][11][12][13]. Since in the presence of light irradiation, photocatalytic materials can degrade organic pollutants (such as oils and greases) adsorbed to their surface, these materials can also be classified as self-cleaning materials, a very important property in road engineering applications, because the self-cleaning function can contribute to a significant reduction of car accidents on oil-spilled areas.…”

Photocatalytic and smart asphalt mixtures: a brief overview

“…In particular, several studies have achieved good results for the degradation of pollutants emitted by fossil fuel vehicles. Due to the huge surface area covered and its vicinity to the exhaust gases from automobile, the photocatalytic road pavements are quoted as promising surfaces for the reduction (in the presence of sunlight and moisture/O2) of NOx, COx, HC and other pollutant gases present in the atmosphere [3][4][5][6][7] . For this reason, by the fact that the photocatalytic materials can degrade organic pollutants (like oils and greases), these materials could also be classified as self-cleaning materials.…”