Photocatalytic and smart asphalt mixtures: a brief overview

Nowadays, there is an increasing concern about the use of less harmful techniques to the environment, and about road safety in Transportation Engineering. Heterogeneous photocatalysis based on the application of semiconductors materials onto asphalt mixtures is a promising technology because it can mitigate air pollution and road accidents. The functionalized asphalt mixtures with photocatalytic capability can degrade pollutants, such as damaging gases and oil/greases over their surface from specific reactions triggered by sunlight photons, providing significant environmental and social benefits. In this communication, a brief review of photocatalysis applied in asphalt mixtures will be presented.

Related papers:

title: Development of photocatalytic asphalt mixtures by the deposition and volumetric incorporation of TiO2 nanoparticles
abstract: The field of construction and building industry was identified as an important market for the use of photocatalytic products since they can be applied to reduce building facades maintenance costs and also the pollution effects, particularly important in metropolis with high population density. The multifunctional capability of these materials will be promoted by the photocatalytic oxidation of pollutant agents. In this research work it was studied and developed a process to produce road pavements formulations with tailored properties that will and promote photocatalytic and self-cleaning effects. This can empower the production of non-slipping surfaces important to avoid accidents that occurs due to the combination of the first autumn rains and adsorbed oils and other organic compounds onto the pavement’s surfaces. To integrate the semiconductor material, two application methods were used: a water-based TiO2 nanoparticles solution, applied by spraying, and using TiO2 nanoparticles by volume incorporation to the base asphalt mixture.

title: Assessment of photocatalytic, superhydrophobic and self-cleaning properties on hot mix asphalts coated with TiO 2 and/or ZnO aqueous solutions
abstract: This work was partially financed by FCT—Fundacao para a Ciencia 
e Tecnologia—under the project PTDC/FIS/120412/2010: 
‘‘Nanobased concepts for Innovative & Eco-sustainable constructive 
material’s surfaces’’ and project PEst-OE/ECI/UI4047/2014 
supported by Portuguese Foundation for Science and Technology.

title: 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-TiO2 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 factors – application procedure, influence of temperature, spraying rate, incorporation percentage and TiO2 immobilization (from traffic and rain removal) – were evaluated based on Rhodamine B (RhB) degradation. For bulk incorporation, the best content nano-TiO2 was 3%. The temperature of the substrate has no influence on the photocatalytic results. The most effective spraying rates were 8 and 16 mL/cm2. 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-TiO2. To have the maximum benefit of the techniques studied, the ideal solution would be the combination of both, with negligible impact on mechanical performance.

title: Sustainable Photocatalytic Asphalt Pavements for Mitigation of Nitrogen Oxide and Sulfur Dioxide Vehicle Emissions
abstract: 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.

title: Titanium dioxide photocatalysis
abstract: Scientific studies on photocatalysis started about two and a half decades ago. Titanium dioxide (TiO 2 ), which is one of the most basic materials in our daily life, has emerged as an excellent photocatalyst material for environmental purification. In this review, current progress in the area of TiO 2 photocatalysis, mainly photocatalytic air purification, sterilization and cancer therapy are discussed together with some fundamental aspects. A novel photoinduced superhydrophilic phenomenon involving TiO 2 and its applications are presented.

title: Photocatalytic degradation of Rhodamine B dye by cotton textile coated with SiO2-TiO2 and SiO2-TiO2-HY composites
abstract: The authors thank CAPES from Brazil for the financial support of this work. This work is also a result of project “AIProcMat@N2020 − Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-FEDER-000006 and the project BioTecNorte (operation NORTE-01-0145-FEDER-000004), supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). This work also has been funded by ERDF through COMPETE2020 − Programa Operacional Competitividade e Internacionalizacao (POCI), Project POCI-01-0145-FEDER-006984 − Associate Laboratory LSRE-LCM and by national funds through FCT − Fundacao para a Ciencia e a Tecnologia for project PTDC/AAGTEC/5269/2014 and Centre of Chemistry (UID/QUI/00686/2013 and UID/QUI/0686/2016).

title: Development of alternative photocatalysts to TiO2: Challenges and opportunities
abstract: Since the early development of this technology in the 1970s, TiO2 constitutes the archetypical photocatalyst due to its relatively high efficiency, low cost and availability. However, during the last decade a considerable number of new photocatalytic materials, either semiconductor or not, have been proposed as potential substitutes of TiO2, particularly in the case of solar applications, for which this standard photocatalyst is not very suitable because of its wide band gap. Semiconductors based on cations with d0 configuration such Ta5+ or Nb5+, as well as oxides or nitrides of d10 elements such as Bi3+, In3+ or Ga3+ are among the most successful novel photocatalysts, but non-semiconductor solids like cation-interchanged zeolites also produce interesting results. In addition, some classical semiconductors like ZnO or CdS, initially discarded as a consequence of their poor stability under irradiation, have been reconsidered as feasible photocatalysts for particular applications. This growing body of data requires new analysis of the challenges and opportunities facing photocatalysis in order to assess which of the photoactive materials are best for each particular application. In this review, we summarize, with an historical perspective, the main achievements obtained with photocatalyst alternatives to TiO2 in the three main niches for this technology: water splitting for hydrogen production, decontamination and disinfection processes, and organic synthesis.

title: Supporting of mixed ZnS–NiS semiconductors onto clinoptilolite nano-particles to improve its activity in photodegradation of 2-nitrotoluene
abstract: Photodegradation of a 2-nitrotoluene (2-NT) aqueous solution was studied using ZnS–NiS supported onto clinoptilolite nano-particles (ZnS–NiS–NCP) and a Hg lamp as the radiation source. A planetary ball-mill was used for preparation of nano-particles of clinoptilolite (NCP). The photocatalyst was prepared via sulfiding of the Zn–Ni exchanged NCP and characterized by Fourier transformation infra red spectroscopy (FT-IR), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS) and transmission electron microscopy (TEM). UV-Vis spectrophotometric measurements were performed for the determination of degradation and mineralization of the pollutant. Degradation of the pollutant was also confirmed by chemical oxygen demand (COD) and high performance liquid chromatography (HPLC). The optimal operation parameters were found to be: 0.75 g L−1 of the ZnS9.7%–NiS3.0%–NCP catalyst and 55 ppm of 2-NT at pH 11. Unsupported ZnS and NiS showed smaller degradation activities than the supported one. The degradation process obeyed first-order kinetics.

title: Increased photocatalytic activity of Zn(II)/Cu(II) oxides and sulfides by coupling and supporting them onto clinoptilolite nanoparticles in the degradation of benzophenone aqueous solution.
abstract: Photocatalytic activity of the coupled ZnO-CuO and ZnS-CuS semiconductors supported onto clinoptilolite nanoparticles (CNP) and micronized one (CMP) was studied in photodegradation of benzophenone (BP) aqueous solution. The ZnO-CuO/CNP (or MCP) and ZnS-CuS/CNP (or MCP) catalysts were prepared via calcination and sulfiding of their Zn(II)-Cu(II) ion-exchanged samples, respectively. XRD patterns confirmed loading of the mentioned semiconductors onto the zeolite, and nano dimension of the catalysts was confirmed by XRD and TEM results. Typical Tauc plots obtained from UV-vis DRS spectra showed red shifts for the band gap energies of the supported coupled semiconductors with respect to the supported monocomponent ones especially for ZnO/NCP and ZnS/NCP catalysts. Also, in both indirect and direct transitions, these red shifts were more considerable in the oxidic systems with respect to the sulfidic systems. Accordingly, the supported oxidic systems showed better photocatalytic activity than the sulfidic one. In the oxidic systems changing the dose of CuO played important role while in the sulfidic systems ZnS played considerable role in the degradation of BP. In the used systems, CuO and ZnS played the main e/h generators in the oxidic and sulfidic systems, respectively, while ZnO and CuS played the preventer e/h recombination. Based on the results, production of e/h is the rate limiting step in the used systems. The maximum degradation activity of the catalysts was obtained at: 0.12gL(-1) of ZnO0.80-CuO3.18/NCP and 0.10gL(-1) of ZnS1.39-CuS2.88/NCP catalysts, initial BP concentration of 30mgL(-1) at pH 7.5.

title: Investigation of the photocatalytic activity of supported ZnO–TiO2 on clinoptilolite nano-particles towards photodegradation of wastewater-contained phenol
abstract: AbstractPhotodegradation of a phenol wastewater sample with ZnO–TiO2 supported on nano-clinoptilolite particles (NCP) was studied. NCP were obtained by planetary ball mill. The proposed catalyst was obtained via ion exchanging of NCP with Zn(NO3)2∙6H2O and C4H10N2O10Ti∙H2O (0.2 M) aqueous solutions for 12 h followed by calcination at 450°C for 12 h. XRD, FT-IR, and TEM were used for characterization of samples. The best degradation efficiency was related to the catalyst containing both ZnO and TiO2. The optimum values were 0.1 g L−1 of photocatalyst, 100 times diluted wastewater solution, and pH of 3.0 in photodegradation studies.

title: Charge carrier trapping, recombination and transfer during TiO2 photocatalysis: An overview
abstract: Heterogeneous photocatalysis mediated by semiconducting TiO2 has attracted continuous interest during the past decades and has shown great potentials in environmental remediation and solar energy conversion. Basically, photocatalysis is initiated by the TiO2 excitation. The generated charge carriers undergo trapping, recombination, and interfacial transfer before proceeding the redox reaction at TiO2 surface. Monitoring the charge carrier dynamics is of particulate importance for understanding the underlying mechanism and designing efficient photocatalysts. This review overviews the recent progress in characterization of charge carrier dynamics. We will present the analytic techniques for monitoring the fate of charge carriers at each elementary photocatalytic step, including charge carrier generation, trapping and recombination inside the photocatalyst, as well as the interfacial charge transfer. The charge carrier dynamics at TiO2/H2O interface, hole transfer reactions for O2 production, and photocatalytic oxidation of organic compounds and nitric oxides, and electron transfer reactions for photocatalytic reduction of viologens and metal ions are addressed, aiming at a deeper understanding of photocatalytic process.

title: Photoactive roadways: Determination of CO, NO and VOC uptake coefficients and photolabile side product yields on TiO 2 treated asphalt and concrete
abstract: This work reports uptake coefficients and by-product yields of ozone precursors onto two photocatalytic paving materials (asphalt and concrete) treated with a commercial TiO2 surface application product. The experimental approach used a continuously stirred tank reactor (CSTR) and allowed for testing large samples with the same surface morphology encountered with real urban surfaces. The measured uptake coefficient (γgeo) and surface resistances are useful for parametrizing dry deposition velocities in air quality model evaluation of the impact of photoactive surfaces on urban air chemistry. At 46% relative humidity, the surface resistance to NO uptake was ∼1 s cm−1 for concrete and ∼2 s cm−1 for a freshly coated older roadway asphalt sample. HONO and NO2 were detected as side products from NO uptake to asphalt, with NO2 molar yields on the order of 20% and HONO molar yields ranging between 14 and 33%. For concrete samples, the NO2 molar yields increased with the increase of water vapor, ranging from 1% to 35% and HONO was not detected as a by-product. Uptake of monoaromatic VOCs to the asphalt sample set displayed a dependence on the compound vapor pressure, and was influenced by competitive adsorption from less volatile VOCs. Formaldehyde and acetaldehyde were detected as byproducts, with molar yields ranging from 5 to 32%.

title: Laboratory Evaluation of Environmental Performance of Photocatalytic Titanium Dioxide Warm-Mix Asphalt Pavements
abstract: 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...

title: Durability of NO Oxidation Effectiveness of Pavement Surfaces Treated with Photocatalytic Titanium Dioxide
abstract: Nowadays, photocatalysis has demonstrated to be a reliable solution in order to purify the atmosphere from the pollutants originated by vehicular traffic. Owing to the primary importance of this problem, the potential of innovative photocatalytic techniques, dealing with the immobilization of titanium dioxide TiO2 on the surface of the asphalt pavement, has been investigated. In particular, three different products, two bituminous emulsions and a cement mortar, were applied on the right lane and on the emergency lane of a highway section in Italy. The effectiveness of the photocatalytic treatments and its evolution with time were evaluated on cores taken after 1, 17, 46, 88, 218, and 527 days from the application of the products. Two tests were carried out on the cores: The NO degradation was evaluated through continuous flow tests, and the size of the treated areas was quantified by means of digital image analysis methods. The research showed interesting results, as all the techniques, in particular the bituminous emulsion-based products, proved to have a good effectiveness in air de-polluting, even if a decay of performance was noted, depending of traffic and weather conditions.

title: Evaluating photocatalytic asphalt pavement effectiveness in real-world environments through developing models: a statistical and kinetic study
abstract: Photocatalytic asphalt pavements are evaluated in this study as a possible air-pollution reduction strategy and to comprehend their behaviour in the real-world environment. Statistical models from real-world experiments or reaction kinetics are two approaches to understand the photocatalytic reduction in real-world environments. The objective of this study was to develop a statistical model for nitrogen oxide (NO) reduction using data from a field study and to evaluate the photocatalytic reaction kinetics of NO reduction, which could be used in future theoretical air-pollution model simulations. To achieve this objective, a photocatalytic water-based spray coating was applied on an existing asphalt pavement site for the field study statistical model and on laboratory samples for the kinetic study. Based on the field data, the NO reduction was modelled using statistical regression techniques by creating a model for a non-coated pavement and photocatalytic pavement. The coefficient of determination was 0.79 and 0.67, respectively. To improve prediction, other parameters may need to be included into the model and more sampling time is required. Based on the laboratory results, the NO reduction was reaction controlled following the Langmuir–Hinshelwood (L–H) model. The adsorption equilibrium constant calculated for photocatalytic asphalt pavements was similar to those of concrete pavements while the reaction rate constant was significantly lower. While humidity has a negative correlation on both L–H constants, intensity has a positive correlation. However, interaction between these two parameters exists.

title: Photocatalytic degradation of vehicle exhausts on asphalt pavement by TiO2/rubber composite structure
abstract: In order to improve the efficiency and durability of semiconductor photocatalyst for degrading vehicle exhausts, a highly active degradation micro-unit was designed by crosslinking nano-TiO2 to the surface of fine crumb rubber with coupling agent. The dependence of degradation efficiency of NO2 on preparation parameters and test conditions were studied. Laboratory tests showed that the degradation rate of NO2 could reach 90% under the appropriate test environment such as initial NO2 concentration of 20 mg/m3, a mercury lamp with illumination of 1000 lx, temperature of 25 °C, relative humidity of 50% and rubber powder of 80 mesh. Tunnel tests showed that the concentration of NO2 in test section was 0.1–0.3 mg/m3 lower than those of contrast sections and the degradation rate reached 60% in 1 h. Since a three-dimensional contact area among nano-TiO2, exhausts, moisture and light was formed on the surface of rubber powders, the proposed technology is expected to provide a new way for greatly improving the degradation efficiency of vehicle exhaust by asphalt pavements.

title: Artificial intelligence modeling to evaluate field performance of photocatalytic asphalt pavement for ambient air purification
abstract: 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.

title: NOx removal from vehicle emissions by functionality surface of asphalt road.
abstract: This paper reported the potential of heterogeneous photocatalysis as an advanced oxidation technology for NO(x) removal from vehicle emissions by using TiO(2) as a photocatalyst immobilized on the surface of asphalt road. Based on asphalt road material porous characteristic, we utilized permeability technology to make asphalt nano-TiO(2) to be environmental protection materials. And then using scanning electron microscope, we observed the penetrating effect of TiO(2). The effect of surface friction, humidity and light intensity on NO(x) removal had been systematically investigated by the use of TiO(2) immobilized on the surface of asphalt road as photocatalytic environmental protection materials. In addition, the decontaminating effect was tested by contrast test in TiO(2) spraying section with non-spraying section, while the productions were used in road environment. Results of experiment revealed that decontaminating rate of the productions ranged from 6% to 12% this kind of photochemical catalysis environmental protection material has good environment purification function.

title: Preparation of La-doped nanometer TiO2 and its application for NO removal on asphalt concrete
abstract: La-doped TiO2 nanoparticle was prepared by ultrasonic assisted sol–gel method. Its crystalline phase, surface morphologic structure and optical property were characterised by X-ray diffraction (XRD), scanning electron microscope (SEM) and ultraviolet visible light spectroscope (UV–VIS). The photocatalytic activity of La-TiO2 was evaluated by the degradation of nitric oxide (NO) under visible or ultraviolet irradiation. The results indicate that the photocatalysts exist lattice distortion and grain refinement after the modification, which cause more reactive centres on the surface, lead to the red shift of absorption spectra and the increase of absorption in ultraviolet light region. It concludes that the modified sample with 0.5% dosage of La has the optimal photocatalytic activity. Next, the La-TiO2 nanoparticles were well dispersed in silica sol and then loaded on the surface of asphalt concrete specimens, and the specimen’s degradation performance of NO was tested by using the self-designed photocatalytic performance tester. The results demonstrate that the specimens present considerable photocatalytic activity under different conditions of light sources, and the NO degradation rates diminish gradually with the increase of NO concentration in the mixed gas and the flow velocity. Under ultraviolet light and visible light irradiation, the NO degradation rates are 39.37% and 19.7%, respectively.

title: Investigation of Ce-TiO2 photocatalyst and its application in asphalt- based specimens for NO degradation
abstract: In order to improve the photocatalytic activity of TiO2 and apply it in asphalt pavement to degrade the pollutants in atmosphere, cerium nitrate was used as the doping source to prepare the Ce doped TiO2 photocatalyst and the crystal structure and electronic structure of the Ce-TiO2 were calculated by the First Principles. The results show that the doping of Ce causes these phenomena: a distortion in the crystal lattice, a shifting of the center of the positive and negative charge in the crystal, a reduction of orbital degeneracy and an increase of the number of excited electrons. These leads to an improvement in the photocatalytic ability of TiO2. Secondly, the photocatalytic activity of Ce-TiO2 was evaluated by the photodegradation test of methylene blue (MB). The study found that the degradation efficiency showed a trend of first rising and then falling with the increase of Ce contents. Finally, photocatalytic asphalt-based specimens were prepared by direct mixing, surface spraying, Ce-TiO2 coating and zeolite particle loading of Ce-TiO2. Relatively speaking, the specimens prepared by the method of surface spraying Ce-TiO2 dispersion have a better NO removal effect.

title: Durability of epoxy-bonded TiO2-modified aggregate as a photocatalytic coating layer for asphalt pavement under vehicle tire polishing
abstract: A new approach to construct photocatalytic air-purifying asphalt pavements coated with TiO 2 modified aggregate was developed and its feasibility and performance were evaluated. Two methods, namely the surface coating and pore filling methods, were adopted to produce the TiO 2 modified aggregate. Their photocatalytic efficiency and mechanical performance under vehicle tire polishing, applied by an Aachen Polishing Machine (APM), were investigated and compared. Results indicated that it is feasible to build durable photocatalytic pavement using the new approach and material spreading process reported in this study. Both TiO 2 modification methods provided the spreading aggregate with excellent and comparable NO degradation rates before polishing; however, the pore filling method provided better long-term NO degradation efficiency. The spreading aggregate modified by either method showed excellent long-term skid resistance and surface texture properties after vehicle tire polishing.

title: Photocatalytic asphalt pavement: the physicochemical and rheological impact of TiO2 nano/microparticles and ZnO microparticles onto the bitumen
abstract: A cost-effective solution to provide asphalt pavements with the photocatalytic property was addressed for the first time, based on the combination of low percentages of two semiconductors, TiO2 and ZnO. Two photocatalytic techniques – spray deposition and bitumen modification – were used. With the former, the chemical properties were evaluated by FTIR after spraying the bitumen samples with two aqueous solutions, one with acid PH and another alkaline, of nano-TiO2. The solution with less chemical impact was the alkaline one. With the latter, Penetration, Softening Point, Mass Loss, Dynamic Viscosity, Complex moduli and Performance Grade, after the modification by TiO2 nano/microparticles and ZnO microparticles, were analysed with two levels of ageing produced by the RTFOT. TiO2 nano/microparticles and ZnO microparticles conducted to softer bitumens and better results of short-term ageing resistance and did not cause any deterioration to the bitumen before or after either short- or long-term ageing.

title: Improving aging resistance and fatigue performance of asphalt binders using inorganic nanoparticles
abstract: The use of inorganic nanoparticles in asphalt binders and mixtures to improve performance related properties have gained a popularity in recent years. Extremely large interface area with asphalt binder matrix is the most important feature of these nanoparticles which translates in a higher degree of changes in the microstructure of asphalt binder. In this research, different inorganic nanoparticles of SiO2, TiO2 and CaCO3 were mixed with asphalt binder and the chemical and microstructural properties of the nanocomposites were evaluated using X-ray diffraction and scanning electron microscopy, respectively. The effect of oxidative aging has been investigated using Fourier Transform Infrared spectroscopy as well as the determination of viscoelastic properties of the modified binders. Furthermore, strain-controlled Time Sweep and Linear Amplitude Sweep tests were used to evaluate the performance of nanocomposites against fatigue cracking. The results indicated improved aging resistance by addition of TiO2 and CaCO3 nanoparticles to asphalt binder. Moreover, nano silica enhanced fatigue properties in the whole range of strain levels. However, different variables such as additive content and strain level affected the fatigue behavior of TiO2 and CaCO3 modified binders.

title: Study on Anti-Ultraviolet Radiation Aging Property of TiO2 Modified Asphalt
abstract: In order to decrease the disadvantageous effect of ultraviolet light to asphalt, nano-scaled TiO2 was selected as modifier to modify asphalt. The photooxidation properties of the modified asphalt were examined in a home-made ultraviolet radiation environment box. By comparing the before and after performance indexes of asphalt, the anti-photooxidation aging property of modified asphalt and the blank asphalt were studied. And the results showed that the sample of 5% TiO2 modified asphalt possesses more stable ductility and smaller softening point changing ratio.TiO2 doping can actively enhance the photooxidation properties of asphalt and TiO2 modified asphalt is capable of resisting photooxidation aging.

title: Photocatalytic pavements with epoxy-bonded TiO2-containing spreading material
abstract: Titanium dioxide (TiO 2 ) is a photocatalyst which can accelerate the oxidation of nitrogen oxides (NO x ) and other pollutants under ultraviolet (UV) radiation. In this study, a new method to coat TiO 2 onto asphalt pavements was developed with the aim to enhance the NO x decomposition efficiency and durability of the coating material for asphalt pavements. In this method, pulverized TiO 2 -cement mortar is used as the spreading material, which is bonded to asphalt pavement surface by epoxy resin. The composition of the TiO 2 -cement mortar was optimized in terms of its mechanical properties. The long-term NO x degradation efficiency, abrasion resistance, and skid resistance of the spreading material were measured after it was subjected to 300 min polishing by the advanced Aachen Polishing Machine (APM). It was concluded that durable NO x degradation efficiency can be achieved by the developed method and the method is feasible for practical implementation.

title: Novel method of coating titanium dioxide on to asphalt mixture based on the breath figure process for air-purifying purpose
abstract: Titanium dioxide (TiO₂) is a photocatalyst that has the capability of accelerating the oxidation of nitrogen oxides (NOₓ) and other pollutants under ultraviolet (UV) radiation. A number of studies have been conducted on applying TiO₂ onto pavement surface to purify exhaust emissions from vehicles. However, it remains a challenging task to effectively coat TiO₂ to asphalt pavements to achieve durable air-purifying performance. This study aims to develop an innovative method, based on the breath figure (BF) process and Pickering emulsion effect, to coat TiO₂ particles onto asphalt pavement surfaces. With this method, asphalt binder with micro pores filled with TiO₂ particles can be coated to asphalt pavement surfaces. The micro porous structure of the coating material helps to provide larger contact area between TiO₂ and UV, thus enhancing NOₓ degradation efficiency. Microscopic analysis on the coating material prepared using the new method demonstrated that TiO₂ particles distributed well on the pore walls of the coating material, indicating that UV can reach TiO₂ to activate the photocatalytic process. The nitric oxides (NO) removal efficiencies of the asphalt mixture specimens coated using this new method and the traditional water solution-based method after various numbers of surface abrasions were also measured by a custom-designed environmental test setup. It was found that this new coating method provided not only better NO removal efficiency, but also improved durability to maintain the degradation efficiency after tire abrasion, compared to the traditional method.

title: Synthesis of iron-doped TiO2 nanoparticles by ball-milling process: the influence of process parameters on the structural, optical, magnetic, and photocatalytic properties
abstract: Titanium dioxide (TiO2) absorbs only a small fraction of incoming sunlight in the visible region thus limiting its photocatalytic efficiency and concomitant photocatalytic ability. The large-scale application of TiO2 nanoparticles has been limited due to the need of using an ultraviolet excitation source to achieve high photocatalytic activity. The inclusion of foreign chemical elements in the TiO2 lattice can tune its band gap resulting in an absorption edge red-shifted to lower energies enhancing the photocatalytic performance in the visible region of the electromagnetic spectrum. In this research work, TiO2 nanoparticles were doped with iron powder in a planetary ball-milling system using stainless steel balls. The correlation between milling rotation speeds with structural and morphologic characteristics, optical and magnetic properties, and photocatalytic abilities of bare and Fe-doped TiO2 powders was studied and discussed.

title: Durability Quantification of TiO2 Surface Coating on Concrete and Asphalt Pavements
abstract: AbstractThe use of nanosized titanium dioxide in photocatalytic pavements is a promising approach to combat air pollution. Past research focused on the effects of environmental and operational parameters on photocatalytic efficiency and its performance under laboratory and field conditions. Few studies have attempted to quantify the durability of the technology integrated with in-service photocatalytic pavements. This study developed and tested a new photocatalytic quantification method used to quantify the short-term durability of a TiO2 spray application on two pavement surfaces: concrete and asphalt. This was accomplished through developing a nitrate extraction method that could be used on in-service pavements without requiring core extraction. Results of the proposed method were compared to results obtained from the Japanese Industrial Standards (JIS) method. The experimental program included testing photocatalytic samples in the laboratory for NOx reduction and nitrate accumulation based on the JIS m...