Avaliação das capacidades fotocatalítica, superhidrofóbica e autolimpante de misturas betuminosas funcionalizadas com TiO2 e ZnO

Dissertação de mestrado integrado em Engenharia CivilAtualmente, existe uma preocupação crescente acerca do esgotamento dos recursos naturais e do dano ao meio ambiente. A engenharia rodoviária em geral e particularmente o domínio dos pavimentos rodoviários pode contribuir de forma significativa para a mitigação destes problemas. A integração de nano/micromateriais nas misturas asfálticas que constituem as camadas superficiais dos pavimentos dotará essas superfícies de novas capacidades (funcionalização) particularmente em termos ambientais e em termos de segurança viária: (i) fotocatalíticas: capazes de fotodegradarem poluentes com o intuito de limparem o meio ambiente; (ii) superhidrofóbicas: melhor resistência à água e uma maior segurança rodoviária em períodos de chuva e de baixas temperaturas; (iii) autolimpantes: evitar problemas de derrapagem, facilitar a drenabilidade da água e dificultar o fenômeno da colmatação dos poros. Com o objetivo de dotar as superfícies dos pavimentos com estas novas capacidades funcionais, misturas asfálticas do tipo AC 6 e AC 14 foram funcionalizadas a partir da aspersão superficial dos semicondutores nano-TiO2 e/ou micro-ZnO. Previamente, a fim de avaliar o impacto químico e morfológico da aplicação dos semicondutores, foram realizados ensaios de Microscopia de Força Atômica (AFM) e Espectroscopia de Infravermelho Transformada de Fourier (FTIR) nos ligantes asfálticos usados para compor as misturas. A seguir, para verificar as novas capacidades, foram realizados ensaios de Ângulo de Contato e de Avaliação Fotocatalítica. Por fim, a melhor solução foi avaliada mecanicamente pela resistência à tração após o condicionamento por água para avaliar o impacto dos semicondutores. Os resultados indicam que houve um maior impacto superficial e químico pela técnica de aspersão da solução aquosa contendo ZnO. A combinação de TiO2 com ZnO promoveu propriedades fotocatalíticas, superhidrofóbicas e auto-limpantes, proporcionando a ambas as misturas asfálticas essas novas capacidades. Ademais a aspersão não causou impacto mecânico. Com o desenvolvimento dessas camadas, prevêem-se grandes benefícios para o ambiente e para a segurança rodoviária.Presently, there is a growing concern about the depletion of natural resources and environmental damage. The road engineering in general and road pavements can contribute significantly to mitigate these problems. The integration of micro/nanoparticles in asphalt mixtures that compose the top layer of the pavements will provide their surfaces with new capabilities (functionalization) particularly in environmental and safety related terms: (i) photocatalytic: able to photodegrade pollutants for the purpose of cleaning the environment; (ii) superhydrophobic: better water resistance and better road safety in periods of rains and low temperatures; (iii) self-cleaning: avoid slipping problems, facilitate the water drainability and prevent the pore clogging phenomenon. In order to provide the new functional capabilities to the surface of the pavements, asphalt mixtures AC 6 and AC 14 were functionalized with superficial spraying of semiconductors nano-TiO2 and/or micro-ZnO. First, in order to evaluate the chemical and morphological impacts of the application of the semiconductors, tests of Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR) onto the asphalt binder that compose the mixtures were carried out. Next, in order to verify the new capabilities, tests of Water Contact Angle and Photocatalytic Evaluation were carried out. Finally, the best solution was mechanically evaluated through Indirect Tensile Strength after immersion to analyze the impact of semiconductors. The results show that there was a higher superficial and chemical impact onto the bitumen by the spray technique of the ZnO aqueous solution. The combination of TiO2 and ZnO promoted photocatalytic, superhydrophobic and self-cleaning properties, providing the asphalt mixtures these new capabilities. Besides the spraying technique did not cause mechanical impact. With the development of these layers, benefits to the environment and road safety are foreseen

Photocatalytic and thermochromic materials applied to road engineering

[Excerpt] Materials Science knowledge has been applied to Civil Engineering to provide new capabilities and benefits for the environment and society. Through the functionalization process with nano/microparticles, Civil Engineering materials can become smart. This study presents the main results of the research work with photocatalytic (nano-TiO2 ) and thermochromic (Leuco dye) materials on road pavements and road markings [1-5]

Are there new ways to improve the asphalt mixtures' surface functions? For sure! By functionalization process

Titanium Dioxide (TiO2) semiconductor material and Polytetrafluorethylene (PTFE) have been applied in the form of nano/microparticles over asphalt road pavements to provide them with new surface functionalities. This is a FUNCTIONALIZATION process that aims to improve the sustainable characteristics of the asphalt mixtures through the photocatalytic, superhydrophobic, and self-cleaning capabilities, which are related to the degradation of hazardous pollutants from the atmosphere (NOx, SO2, among others) for environmental remediation and the cleaning of the road surface (dust, greases, and oils) for the mitigation of the decrease of friction. Thus, in this research work, dispersions containing TiO2 nanoparticles and PTFE microparticles were sprayed over an AC 10 asphalt mixture to coat and functionalize it. To confirm the photocatalysis, super hydrophobicity, and self-cleaning capacities, this smart material performance was evaluated under the degradation of the organic compound Rhodamine B (RhB) as a pollutant model and Water Contact Angle (WCA). The results indicate the photodegradation of the pollutant, confirming the proper functioning of the functionalization process, and a WCA of 150°, proving that the nanoparticles were well dispersed just over the surface of the asphalt mixture. In general, this multidisciplinary research contributes to social and environmental enhancement and enlarges the opportunities for applications of nanomaterials in a very large-scale field such as Civil Engineering. Moreover, it showed that the surface characteristics of the asphalt pavements could be studied and improved not only with a conventional approach based on noise, friction, texture, and rolling resistance measurements but also through a physicochemical approach, as the functionalization processes, using knowledge of Materials Science

Assessing photocatalytic asphalt mixtures: practical and laboratory methods for measuring air quality

Air pollution in urban areas has become a major global concern, leading to a series of programs and regulations to be implemented to reduce it. Among the various pollutants that affect air quality is nitrogen monoxide (NO), which, once in the atmosphere, oxidizes into nitrogen dioxide (NO2). The combination of NO and NO2 refer to the nitrogen oxides (NOx), which, besides being harmful to health, have a negative impact on the environment with acid rain and intensify the greenhouse effect. This issue is exacerbated in large cities due to the high concentration of pollutant-emitting vehicles. To mitigate this problem by cleaning the air, researchers are investing in photocatalytic capability that can be applied to the surface of various substrates. Titanium dioxide (TiO2) is a highly utilized material, especially when aiming to attain both photocatalytic and self-cleaning abilities. The application of TiO2 over asphalt pavements has become an important topic in Transportation Engineering as a way of functionalized conventional pavement into a substrate where it becomes feasible to alleviate the environmental damage related to pollutant emissions, mainly NOx. The application of photocatalytic materials on asphalt pavements has the necessary conditions to increase the success of reducing pollutant levels. Pavements present a large area and are closer to vehicle exhausts. In addition, a major part of asphalt pavements is exposed to sunlight, which can activate the photocatalytic reaction. Due to these benefits, researchers have conducted studies that evaluate photocatalytic efficiency on surfaces of asphalt pavements.When evaluating photocatalytic efficiency, the literature describes a series of methods based on laboratory and field tests. In the laboratory, efficiency can be evaluated by degrading different organic dyes and degradation gas tests. For the first method, some dyes are widely used, such as methylene orange (MO), methylene blue (MB) and rhodamine B (RhB). For testing, samples of asphalt mixtures are immersed in an initial dye solution and exposed to light irradiation. Over time, changes in the solution absorbance (and, consequently, concentration) are monitored using spectrophotometry. The photocatalytic efficiency is calculated as a function of the maximum absorbance of the dye and the time. The second test follows the ISO 22197-1 standard, which specifies a test method for determining the air purification performance of materials with photocatalysis on the surface. To simulate and ensure the photocatalytic reactions occur, the experimental setup must contain an air compressor, pollutant source, humidifier, photoreactor, light source and pollutant analyzer. The photocatalytic asphalt mixture sample is placed inside the photoreactor and exposed to a controlled amount of pollutants, light and humidity. The gas flow is continuously injected into the photoreactor and subjected to light irradiation, and gas concentration is monitored over a period of time. The photocatalytic efficiency can be assessed by the net amount of pollutants that the sample removes.In field applications, one method that can be used to evaluate the efficiency is the air quality monitoring stations by conducting a comparative analysis of pollutant concentrations in a specific area before and after installing photocatalytic asphalt pavements. Those stations have sensors that collect outdoor air and distribute it through analyzers. These analyzers continuously and automatically measure various atmospheric pollutants, determining their concentrations in the ambient air "in real-time". Typically, they are fixed at strategic points in large cities, limiting assessment in more remote locations. Usually, these stations can measure several types of pollutants, such as NOx, SO2, CO2, particulate matter, among others, and the meteorological conditions, for example temperature, relative humidity, wind speed and direction , etc. Another method to evaluate the performance in field studies is to use passive sampling. The passive sampling approach is a low-cost, non-electrical, and simplified solution for the distribution of samples. The principle of the passive sampler involves gas collection through the diffusion of atmospheric air, which enters the device through one of its ends, travels through the body of the sampler (in the form of a tube) until it reaches its other end, which is sealed and contains a filter paper previously impregnated with a specific absorbent solution designed to react with the targeted pollutant to be collected. Measurement of photocatalytic efficiency is crucial in determining the performance of photocatalytic pavements and their impact on air quality. Thus, this study aims to provide a comprehensive elucidation of how to evaluate the photocatalytic efficiency of photocatalytic asphalt pavements functionalized with TiO2 nanoparticles through various methods, encompassing laboratory approaches and field studies.This research was funded by FCT: NanoAir PTDC/FISMAC/6606/2020, MicroCoolPav EXPL/EQU-EQU/1110/2021, UIDB/04650/2020, UIDB/04029/2020, 2022.00763.CEECIND and 2023.02795.BD. Also, it was funded by FUNCAP: MLC-0191-00144.01.00/22 and CNPq: 404978/2021-5 – Chamada CNPq/MCTI/FNDCT Nº 18/2021.

Smart asphalt mixtures: a bibliometric analysis of the research trends

A smart asphalt mixture holds new capabilities different from the original ones or can react to a stimulus. These capabilities can be categorized based on smartness or function: smartness, mechanical, electrical, optical, energy harvesting, electromagnetic wave/radiation shielding/absorbing, and water related. The most important capabilities applied to asphalt mixtures are the photocatalytic, self-cleaning, self-healing, superhydrophobic, thermochromic, deicing/anti-icing, and latent heat thermal energy storage abilities. This research deals with a bibliometric review of the peer-reviewed journal articles published on the Scopus database, with the strings of terms related to these capabilities and asphalt or bitum in their titles, abstracts, and keywords. The review analysis highlighted the increasing number of accumulated publications, confirming the relevance of this research topic in recent years. The capability most often referred to was self-healing. The study showed that China was the most productive country. Research articles were mostly published in the journal Construction and Building Materials. Several techniques and methods are being developed regarding smart asphalt mixtures; for that reason, this research work aims to evaluate the literature under a bibliometric analysis.This research was funded by the Portuguese Foundation for Science and Technology (FCT), NanoAir PTDC/FIS-MAC/6606/2020, MicroCoolPav EXPL/EQU-EQU/1110/2021, UIDB/04650/2020, and UIDB/04029/2020. This research was also supported by the doctoral grant 2023.02795.BD, funded by FCT, as well as and bydoctoral grant PRT/BD/154269/2022 financed by the FCT and with funds from POR Norte-Portugal 2020 and State Budget, under MIT Portugal Program. The first author would like to acknowledge the FCT for funding (2022.00763.CEECIND)

Passive sampling for air quality assessment: proposal of an in-situ method to measure the efficiency of photocatalytic pavements

Currently, air pollution is a matter of great relevance due to its significant impact on human health. Semiconductor photocatalysis technology, known for its high efficiency and low environmental degradation, is considered a highly promising means to improve air quality. Asphalt pavements are commonly used in urban areas with high population concentrations. During the production cycle of these pavements, various air pollutants are emitted, primarily due to the high temperatures required for asphalt pavement. Photocatalysis using the semiconductor TiO2 has the capacity to degrade atmospheric NO under sunlight, which has sparked significant interest in photocatalysis technology and its applications.The bandgap, enduring physicochemical properties of the element, and its nontoxicity, along with its NO degradation capabilities, make TiO2 a highly viable option for photocatalysis. This study aims to elucidate how air quality is controlled through passive sampling for the quantification of nitrogen dioxide (NO2) in the atmosphere. Through this technique, it is possible to quantify the level of pollutants, in this case, NO2, present in the atmosphere at a selected location over a certain period of time.MicroCoolPav EXPL/EQU-EQU/1110/2021, UIDB/04650/2020, UIDB/04029/2020, 2022.00763.CEECIND and 2023.02795.BD. Also, it was funded by FUNCAP: MLC-0191-00144.01.00/22 and CNPq: 404978/2021-5 – Chamada CNPq/MCTI/FNDCT Nº 18/2021

Evaluation of air cleaning using functionalized asphalt mixture sprayed with TiO 2 nanoparticles

[Excerto] Photocatalytic asphalt mixtures have gained attention as a possible alternative to mitigate the air pollution in urban areas. The asphalt surface when functionalized with nano-TiO2 can reduce nitrogen oxides (NOx), a harmful pollutant emitted by vehicles that contributes to problems such as acid rain and public health concernsCT/MCTES sponsored this research by the projects NanoAir PTDC/FISMAC/6606/2020, MicroCoolPav EXPL/EQU-EQU/1110/2021 and UIDB/04650/2020, under the R&D from ISISE (UIDB/04029/2020) and the ARISE (LA/P/0112/2020). Also, the second and third authors would like to acknowledge the FCT for funding PRT/BD/154269/2022, 2022.00763.CEECIND, respectively

Review on the incorporation of phase change materials (PCM) into asphalt mixtures to mitigate urban heat Island

Serious environmental problems are attributed to the uncontrolled growth of cities. Usually, highly populated areas suffer from soil sealing caused by the construction of infrastructure, such as road pavements and buildings. Regarding the Transportation Engineering, the most common material applied in road pavements is bitumen as binder constituent. Usually dark-coloured, the surface temperature of asphalt pavements may reach values higher than 60 °C during summer. This fact can significantly contribute to the formation of thermal cracks and deformations in asphalt binders and, in large urban centres, promote the formation of warmer microclimates since all the accumulated heat is released to the surrounding environment. The formation of Urban Heat Islands (UHI), a type of microclimate that arises from the increase in temperature of a location that does not match the region, caused by anthropic changes, for some time now, is a problem that has attracted a range of research to minimise harmful effects caused to the environment. Some of the most promising studies to decrease the temperature of pavements are using Phase Change Materials (PCM). PCM are materials that can accumulate a large amount of thermal energy and are widely used in the textile industry, smart tissues, and construction, improving thermal comfort. PCM can minimise the problems arising from seasonal temperature variations when used in conjunction with asphalt materials. In this work, a review was made about which types of PCM are mainly used to achieve a significant decrease in pavement temperature—evaluating the material's thermal performance and the most used strategies to avoid its leakage. A systematic review of recent papers published in peer-reviewed journals (available in the Scopus database) involving asphalt mixtures with phase change materials revealed that the most used type of PCM is polyethylene glycol (PEG). Asphalt mixtures containing PCM generally have lower mechanical performance than conventional asphalt mixtures. There are problems related to leaking the material into the asphalt, sometimes reaching the soil and possibly causing contamination. On average, the temperature values decrease 4 °C, in some cases reaching 9 °C of difference, compared to conventional asphalt-based binders. To avoid leaking of this material, the most applied strategy is the PCM encapsulation within particles composed of silicon dioxide (SiO2) or polyacrylamide (PAM). According to the literature surveyed, it can be concluded that incorporating PCM into asphalt pavements can mitigate the formation of UHI acting as a thermoregulation factor, with acceptable mechanical and improved environmental performance

Study of the composition of coaxial microfibers with phase change materials under thermal analysis

Asphalt pavements cover a large area of urban centers and are directly related to Urban Heat Islands (UHI). These materials heat up by absorbing a large amount of solar energy and then slowly release it, generating environmental, economic and social impacts that directly harm the well-being of citizens. The use of Phase Change Materials (PCM) in asphalt mixtures is indicated in the literature as an efficient thermoregulation method to mitigate UHI. However, their direct incorporation in asphalt mixtures presents some disadvantages related to modifying the asphalt structure after PCM melting. The development of Coaxial Polymeric Fibers (CPF) emerges as an innovative alternative to incorporate PCM in asphalt mixtures. Thus, the research herein reported aims to produce and select the best composition of coaxial fibers composed of Polyethylene glycol (PEG) as PCM and core and cellulose acetate (Mn: 30,000 and 50,000) as sheath. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used for thermal characterization. TGA was used to analyse whether the materials could tolerate the mixing and compaction temperatures of the asphalt mixtures (up to about 200°C) without any mass loss, and DSC to assess the melting point for the CPF. Thereby it is possible to determine the effect of cellulose acetate molecular weight on the phase change temperature of PEG inside the CPF. This information will aid in deciding on suitable materials for asphalt concrete mixtures capable of withstanding asphalt mixing temperatures

Photocatalysis of functionalised 3D printed cementitious materials

The main objective of this study was to evaluate the photocatalytic behaviour of 3D printed cementitious mortars that were functionalised with TiO2 nanoparticles. This study is one of the few available regarding functionalisation of 3D concrete printing (3DCP) with photocatalytic properties. Despite the fact 3DCP research is swiftly growing, it is still necessary further investigation to fully understand these materials’ physicochemical and mechanical properties, which will influence the functionalised properties of the composite. Due to the freeform nature of the 3DCP there are no moulds, therefore the functionalisation through coating can be performed in a much earlier stage than in conventional moulded concrete. The developed smart 3D printed concrete could promote the photodegradation of pollutants for self-cleaning and air purification. In particular, this study investigated the effect of two parameters on photocatalytic behaviour: light power intensity and the coating rate of nano-TiO2 particles. Surface coating was adopted as the functionalisation method, and the Rhodamine B dye degradation efficiency was used as an indicator to evaluate the photocatalytic behaviour. Additionally, the surface roughness and microstructure of the 3D printed cementitious mortar specimens were assessed to distinguish between the reference and TiO2 coated series. Scanning electron microscopy (SEM), X-ray Energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) crystallography were carried out as three techniques to evaluate the morphology, composition, and microstructure of the specimens, respectively. The results indicated successful activation of catalyst particles under illumination, where higher light power intensity increased the degradation efficiency. Furthermore, dye degradation efficiency increased with increasing coating rates of nano-TiO2 particles on the surface of the specimens. The roughness of the 3D printed specimens’ surface was sufficient for settling the nano-TiO2 particles. Finally, microscopy results confirmed the presence and suitable distribution of the nano-TiO2 particles on the surface of the coated specimens.Support SECIL, SIKA, ELKEM and UNIBETAO, which graciously provided the required materials for printing the cementitious specimensThis work was partly financed by Fundaç˜ao para a Ciˆencia e a Tecnologia (FCT)/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. The authors acknowledge the support of DST group construction company for funding the project Chair dst/IB-S: Smart Systems for Construction. The first two authors would like to acknowledge the PhD grants SFRH/BD/143636/2019 and SFRH/BD/137421/2018 provided by the Portuguese Foundation for Science and Technology (FCT). Additionally, the authors would like to acknowledge FCT for the financing this research work by the project NanoAir PTDC/FIS-MAC/6606/2020 and the Strategic Funding UIDB/04650/ 2020–2023