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Pervious concrete with titanium dioxide as a photocatalyst compound for a greener urban road environment
Get PDFThe United States is facing the problem of controlling air pollution from vehicle emissions, especially in growing urban areas. The photocatalyst, titanium dioxide (TiO2), activates with ultraviolet (UV) radiation to oxidize air pollutants, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). Applying the photocatalytic effect of TiO2 onto pervious concrete pavement to remove pollutants from the air appeared to be a promising alternative to remove pollutants from street level. This study compared different methods to apply TiO2 onto the surface of pervious concrete and measured the effectiveness of the surface coating materials in removing air pollutants, maintaining infiltration properties, and withstanding environmental weathering. A brief analysis on the material cost of each application method is also presented. High pollutant reductions were seen with a driveway protector mix, a commercial water based TiO2 preparation, TiO2 in water, a cement-water slurry with low cement concentration, and the commercial PURETI coating. It was found that nitric oxide (NO) was efficiently removed with each of these treatments, while VOCs displayed more variability in removal efficiency. When pervious concrete was compared to traditional concrete, pervious concrete showed higher NO reductions. Most coating methods maintained an acceptable level of infiltration rate for pervious concrete pavements. The driveway protector mix had the highest resistance against freeze-thaw testing with deicing chemical and environmental weathering. The evaluated coating methods are recommended for different applications. The driveway protector mix resists environmental weathering well and can be used for highway shoulders and locations where weathering could be a concern. The transparent color of the commercial water-based TiO2 could be used for aesthetic reasons. The cement aggregate mixes could be used as a thin pervious concrete overlay to at the same time address minor pavement surface distress. The PURETI treatment is a cost-effective alternative, where the surface abrasion is low. More studies need to be done to optimize each application method and confirm their resistance against live traffic and environmental damage. Fundamental research should also be conducted to investigate the sequential chemical reactions during the complex photocatalytic process to substantiate the environmental benefits of the photocatalytic materials in the field
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Quantification of cohesive healing of asphalt binder based on dissipated energy analysis
Get PDFThe effect of healing on asphalt material fatigue performance has been considered as an important property which is, at least partially, responsible for the significant difference between the laboratory and the field fatigue behavior. Although many studies have been conducted to characterize the asphalt healing and its mechanisms, very few researchers have clearly identified how different loading conditions can influence the effect of healing in a quantitative way. In addition, few suggestions have been provided on how to integrate the effect of healing to pavement design. This study develops fundamental dissipated energy analysis to quantify cohesive healing in asphalt binder. The key impact factors on healing are evaluated in to a systematic way under different loading and temperature conditions. Healing rate prediction model, modified fatigue life prediction model taking into account the effect of healing, and plateau value prediction model based on relative simple binder dynamic shear rheometer testing are developed, which can be used for a more accurate prediction of asphalt binder fatigue life. The methodology used in this study may also be applied to investigate and quantify adhesive healing at the aggregate-asphalt interface when aggregates are introduced into experimental testing
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Design and evaluation of 4.75mm mixture for thin asphalt overlay in Washington State
Get PDFThin overlays with 4.75mm nominal maximum aggregate size (NMAS) mixtures are an alternative pavement preventive maintenance strategy that are becoming more popular in recent years mainly because of their cost effectiveness, ability to be placed in thin lifts, and for using screening stockpiles. Washington State is considering introducing this preventive maintenance strategy after an appropriate evaluation of all aspects of this treatment. The objective of this study was to develop mix designs and evaluate the potential of using 4.75mm NMAS thin overlays for WSDOT considering local conditions. A thorough literature review and agency survey was conducted to determine how 4.75mm NMAS thin overlay could be designed, constructed, and applied appropriately. Four mix designs were developed for high traffic volume roads using two binders (PG70-28 and PG76-28) and two gradations (coarse and medium). The design was based on packing concept to help achieve good aggregate interlock and satisfactory volumetric properties. The cracking, rutting, and moisture resistance of the mixtures were evaluated using laboratory indirect tensile test and Hamburg wheel-tracking test. It was found the PG70-28 coarse graded mixture had the best overall performance results with all mixtures showing good results. Using a life cycle cost analysis (LCCA), the 4.75mm thin overlay was compared to traditional 12.5mm overlays and chip seals for cost effectiveness in Washington State. According to historical data and estimation, it was suggested that 4.75mm thin overlays be cost effective when compared to traditional overlay but not chip seals. 4.75mm thin overlays could be a viable pavement preservation strategy in Washington State. Based on the findings from this study, a draft special provision was also created to assist WSDOT in implementing this mix type into their preventive maintenance program
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Innovative concept for creating an air purification pavement surface coating by atmospheric pressure cold plasma
Get PDFAir pollution from automobiles, in the form of nitrogen oxides (NOx) and volatile organic compounds (VOCs) are increasing continuously due to the rapid development of transportation activities, which can cause a number of environmental and social issues and impact public health. Nano titanium dioxide (TiO2) has been found to have photocatalytic properties, which, under UV light can oxidize and remove VOCs and NOx from the atmosphere. Although TiO2 treated paving materials have great potential to improve air quality, current techniques to adhere TiO2 to substrate materials are either not durable or reduce direct contact of TiO2 with UV light, reducing the photocatalytic effect. To solve this technical difficulty, this study innovatively introduces atmospheric pressure cold plasma (APCP) techniques to transportation engineering to coat TiO2 to pavement. The objective of this study is to test the concept of using APCP techniques to create a durable TiO2 coating on the surface of paving materials to reduce NOx and VOCs at the street level. An APCP generator was developed to produce activated radicals from precursor molecules using high voltage streamers as the plasma source, and to immobilize nano TiO2 powder to substrate pavement materials. Preliminary results are promising, showing that TiO2 can be incorporated successfully into an APCP environment. Evidence of TiO2 has been identified based on field emission scanning electron microscope (FE SEM) images. The TiO2 coated material with APCP shows some ability to reduce nitrogen oxides when exposed to UV light in an environmental chamber. However, such effect is limited which is hypothesized due to either limited deposition rate of the plasma polymerized film or the plasma polymerized film blocking the direct contact of TiO2 with the UV light. Further research is therefore recommended to optimize the APCP generator for improved efficiency. Also a more in depth study should be conducted on the plasma polymerized film and its interaction with the TiO2
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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