Heather Dylla

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

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.

Sustainable Photocatalytic Asphalt Pavements for Mitigation of Nitrogen Oxide and Sulfur Dioxide Vehicle Emissions

The ability of titanium dioxide (TiO2) photocatalytic nanoparticles to trap and decompose organic and inorganic air pollutants render them a promising technology as a pavement coating to mitigate the harmful effects of vehicle emissions. This technology may revolutionize construction and production practices of hot-mix asphalt by introducing a new class of mixtures with superior environmental performance. The objective of this study was to assess the benefits of incorporating TiO2 into asphalt pavements. To achieve this objective, the photocatalytic effectiveness and durability of a water-based spray coating of TiO2 was evaluated in the laboratory. This study also presents the field performance of the country’s first air-purifying photocatalytic asphalt pavement, located on the campus of Louisiana State University. Laboratory evaluation showed that TiO2 was effective in removing NOₓ and SO2 pollutants from the air stream, with an efficiency ranging from 31–55% for NOₓ pollutants and 4–20% for SO2 pollutants. The maximum NOₓ and SO2 removal efficiencies were achieved at an application rate of 0.05 L/m². The efficiency of NOₓ reduction is affected by the flow rate of the pollutant, relative humidity, and ultraviolet (UV) light intensity. In the field, NOₓ concentrations were monitored for both the coated and uncoated sections to directly measure photocatalytic degradation. Furthermore, nitrates were collected from the coated and uncoated areas for evidence of photocatalytic NOₓ reduction. Results from both approaches show evidence of photocatalytic NOₓ reduction. Further field evaluation is needed to determine the durability of the surface coating.

Laboratory Investigation of the Effect of Mixed Nitrogen Dioxide and Nitrogen Oxide Gases on Titanium Dioxide Photocatalytic Efficiency in Concrete Pavements

Nitrogen oxides (NOx) emitted from vehicle exhausts are associated with adverse health effects on the public. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed by using a photocatalyst such as titanium dioxide (TiO2). The main objective of this study was to evaluate the environmental effectiveness of TiO2 coating in photodegrading mixed NO2 and NO gases from the atmosphere. Results of the experimental program determined that increasing the flow rate and NO2/NOx ratio negatively affect the effectiveness of the photocatalytic process. However, within the evaluated range, the titanium content and aggregate gradation had little effect on NOx removal efficiency. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface.

Laboratory Evaluation of Environmental Performance of Photocatalytic Titanium Dioxide Warm-Mix Asphalt Pavements

AbstractThe use of titanium dioxide (TiO2) coating for pavements has received considerable attention in recent years to improve air quality near large metropolitan areas. However, the proper method of applying TiO2 to asphalt pavements is still unclear. This study evaluated the benefits of incorporating TiO2 in the preparation of warm-mix asphalt (WMA). Two application methods to integrate TiO2 were evaluated, a water-based TiO2 solution applied as a thin coating and using TiO2 as a modifier to asphalt binder in the preparation of WMA. On the basis of the results of the experimental program, it was determined that the photocatalytic compound was not effective in degrading NOx in the air stream when used as a modifier to the binder in the preparation of WMA. This could be attributed to the fact that only a small amount of TiO2 is present at the surface. When used as part of a surface spray coating, TiO2 was effective in removing nitrogen oxide (NOx-) pollutants from the air stream with an efficiency rangin...

Characterization of nanoparticles released during construction of photocatalytic pavements using engineered nanoparticles

With the increasing use of titanium dioxide (TiO2) nanoparticles in self-cleaning materials such as photocatalytic concrete pavements, the release of nanoparticles into the environment is inevitable. Nanoparticle concentration, particle size, surface area, elemental composition, and surface morphology are pertinent to determine the associated risks. In this study, the potential of exposure to synthetic nanoparticles released during construction activities for application of photocatalytic pavements was measured during laboratory-simulated construction activities of photocatalytic mortar overlays and in an actual field application of photocatalytic spray coat. A scanning mobility particle sizer system measured the size distribution of nanoparticles released during laboratory and field activities. Since incidental nanoparticles are released during construction activities, nanoparticle emissions were compared to those from similar activities without nano-TiO2. Nanoparticle counts and size distribution suggest that synthetic nanoparticles are released during application of photocatalytic pavements. In order to identify the nanoparticle source, nanoparticles were also collected for offline characterization using transmission electron microscopy. However, positive identification of synthetic nanoparticles was not possible due to difficulties in obtaining high-resolution images. As a result, further research is recommended to identify nanoparticle composition and sources.

Evaluation of Nano–Titanium Dioxide Additive on Asphalt Binder Aging Properties

Photocatalysis compounds such as titanium dioxide (TiO2) can trap and degrade organic and inorganic particles in the air and thus remove harmful air pollutants such as nitrogen oxides (NOx) and volatile organic compounds in the presence of ultraviolet light (sunlight). Despite the rapid development of this technology, current applications are limited to concrete pavement surfaces, which represent only 6% of the national road network in the United States. About 94% of the road network in the United States is surfaced with hot-mix asphalt, a percentage that supports directing future research toward the use of TiO2 coating in flexible pavements. Before this technology is integrated into asphalt pavements, the effects of integrating the additives on the rheological properties of the binder should be investigated. To address this objective, a commercial crystallized anatase-based TiO2 powder was blended with a conventional asphalt binder classified as PG 64-16 at three modification rates (3%, 5%, and 7%). Prepared blends were characterized with the use of fundamental rheological tests and with measurements of the environmental efficiency of the binder in removing part of the NOx pollutants from the air stream. Results of the experimental program indicated that the use of TiO2 as a modifier to asphalt binder was effective in removing part of the NOx pollutants from the air stream. Rheological test results indicated that the addition of TiO2 did not affect the physical properties of the conventional binder. Exposing the binder to ultraviolet light did not appear to accelerate the aging mechanisms in the binder.

Effects of Roadway Contaminants on Titanium Dioxide Photodegradation of Nitrogen Oxides

Nitrogen oxides (NOx) emitted from vehicle exhaust are associated with negative health impacts and are a precursor to ozone production. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can degrade pollutants such as NOx through heterogeneous photocatalysis. Photocatalytic layers include titanium dioxide nanoparticles that can trap and degrade organic and inorganic particles in the air and thus remove harmful gases from the air in the presence of ultraviolet light (sunlight). In addition, their superhydrophilic properties allow them to self-clean in the presence of rain. Although this technology has the potential to support environmentally friendly road infrastructure, the impacts of a number of design and operational parameters on the technologys effectiveness need to be evaluated before full-scale implementation. The objective of this study was to measure the impact of common roadway contaminants on the effectiveness of the ability of photocatalytic roadways to remove NOx from the atmosphere. Three common roadway contaminants were tested—dirt, deicing salt, and motor oil—at two contrasting coverage levels. Results of the experimental program showed that the three contaminant types had a strong negative impact on the photocatalytic NOx removal efficiency. The impact of the coverage of contaminants largely depended on the soilure type, with oil having the largest negative impact. An increase in the flow rate and air relative humidity also resulted in lower NOx efficiencies.

Artificial intelligence modeling to evaluate field performance of photocatalytic asphalt pavement for ambient air purification

In recent years, the application of titanium dioxide (TiO2) as a photocatalyst in asphalt pavement has received considerable attention for purifying ambient air from traffic-emitted pollutants via photocatalytic processes. In order to control the increasing deterioration of ambient air quality, urgent and proper risk assessment tools are deemed necessary. However, in practice, monitoring all process parameters for various operating conditions is difficult due to the complex and non-linear nature of air pollution-based problems. Therefore, the development of models to predict air pollutant concentrations is very useful because it can provide early warnings to the population and also reduce the number of measuring sites. This study used artificial neural network (ANN) and neuro-fuzzy (NF) models to predict NOx concentration in the air as a function of traffic count (Tr) and climatic conditions including humidity (H), temperature (T), solar radiation (S), and wind speed (W) before and after the application of TiO2 on the pavement surface. These models are useful for modeling because of their ability to be trained using historical data and because of their capability for modeling highly non-linear relationships. To build these models, data were collected from a field study where an aqueous nano TiO2 solution was sprayed on a 0.2-mile of asphalt pavement in Baton Rouge, LA. Results of this study showed that the NF model provided a better fitting to NOx measurements than the ANN model in the training, validation, and test steps. Results of a parametric study indicated that traffic level, relative humidity, and solar radiation had the most influence on photocatalytic efficiency.

Field Evaluation of Ability of Photocatalytic Concrete Pavements to Remove Nitrogen Oxides

Numerous laboratory studies have demonstrated the ability of nano and ultrafine titanium dioxide (TiO2) photocatalytic pavements to trap and degrade nitrogen oxides in the air when irradiated with ultraviolet light. However, to understand better how photocatalytic pavements will perform under real-world conditions, field studies are necessary. Quantification of the reduction of nitrogen oxides (NOx) in field studies is difficult and challenging because of the many environmental and operating variables. The objective of this paper is to identify evidence of photocatalytic NOx reduction and to determine the environmental and operating factors that affect efficiencies under real-world conditions. A quarter-mile concrete roadway was sprayed with a photocatalytic coating in Baton Rouge, Louisiana. This section was the first field installation of TiO2 photocatalytic pavement in the United States. NOx concentrations were monitored for both the coated and uncoated sections simultaneously for 3 weeks during the spring season to measure photocatalytic degradation directly. Further, nitrates were collected from the coated and uncoated areas for evidence of photocatalytic NOx reduction. Results from both approaches show evidence of photocatalytic NOx reduction. Environmental factors with significant impact on photocatalytic efficiency include relative humidity, solar intensity, and wind speed and direction.

Quantification of Reduction of Nitrogen Oxides by Nitrate Accumulation on Titanium Dioxide Photocatalytic Concrete Pavement

Field trials of photocatalytic pavements were recently initiated and are being considered by many states (e.g., Virginia, Texas, New York, and Missouri). Results from this study are from the countrys first air-purifying asphalt and concrete photocatalytic pavements on December 20, 2010. The test area was a pavement site located on the Louisiana State University campus in Baton Rouge. The objective of this study was validation of photocatalytic degradation of nitrogen oxides (NOx) at the test site by measuring nitrate salts (NO3) deposited on the pavement surface. With quantification of the nitrate levels produced in the field attributable to photocatalytic activity, measurements were correlated to laboratory test results of NOx reduction efficiency. A field sampling procedure of NO3 deposited on the pavement surface is presented. On the basis of the results of the experimental program, the proposed method to quantify photocatalytic efficiency through nitrate measurements was successful. There was definite evidence that photocatalytic degradation of NOx was taking place in the treated section. In addition, the photocatalytic process was active during the first 4 days followed by a slight decrease in degradation of NOx. Full regeneration of photo catalytic activity took place through a self-cleaning process during a rain event. Six months of traffic and in-service operating conditions had negligible effects on the efficiency of the photocatalytic coating. In addition, there was good agreement between nitric oxide removal efficiency measured in the field after one day of nitrate accumulation and in the laboratory at the same relative humidity.