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Studies on urban heat island (UHI) have been more than a century after the phenomenon was first discovered in the early 1800s. UHI emerges as the source of many urban environmental problems and exacerbates the living environment in cities. Under the challenges of increasing urbanization and future climate changes, there is a pressing need for sustainable adaptation/mitigation strategies for UHI effects, one popular option being the use of reflective materials. While it is introduced as one effective method to reduce temperature and energy consumption in cities, its impacts on multi-dimensional environmental sustainability and large-scale non-local effect are inadequately explored. This paper provides a synthetic overview of potential environmental impacts of reflective materials at a variety of scales, ranging from energy load on a single building to regional hydroclimate. The review shows that mitigation potential of reflective materials depends on a portfolio of factors, including building characteristics, urban environment, meteorological and geographical conditions, to name a few.Precaution needs to be exercised by city planners and policy makers for large-scale deployment of reflective materials before their environmental impacts, especially on regional hydroclimates, are better understood. In general, it is recommended that optimal strategy for UHI needs to be determined on a city-by-city basis, rather than adopting a "one-solution-fits-all" strategy.

Urban heat island (UHI) manifests as the temperature rise in built-up urban areas relative to the surrounding rural countryside, largely because of the relatively greater proportion of incident solar energy that is absorbed and stored by man-made materials. The direct impact of UHI can be significant on both daytime and night-time temperatures, and the indirect impacts include increased air conditioning loads, deteriorated air and water quality, reduced pavement lifetimes, and exacerbated heat waves. Modifying the thermal properties and emissivity of roofs and paved surfaces and increasing the vegetated area within the city are potential mitigation strategies. A quantitative comparison of their efficacies and costs suggests that so-called cool roofs are likely the most cost-effective UHI mitigation strategy. However, additional research is needed on how to modify surface emissivities and dynamically control surface and material properties, as well as on the health and socioeconomic impacts of UHI.

The objective of this research study was to evaluate several mathematical models to be used in calculating the onset of tertiary flow [referred to as the flow number (FN) parameter] for asphalt mixtures. The FN indicates the onset of shear deformation in asphalt mixtures, which is a significant parameter in evaluating rutting in the field. The FN is obtained from the repeated load permanent deformation (RLPD) laboratory test. Current modeling techniques in determining the FN use a polynomial model fitting approach, which works well for most conventional asphalt mixtures. However, analysis and observations on the use of this polynomial model for rubber-modified asphalt mixtures showed problems in identifying the true FN values. The scope of the work included the collection and analysis of more than 300 RLPD test data files, which comprised more than 40 mixtures, a wide range of test temperatures, and several stress levels. A new comprehensive mathematical model was recommended to accurately determine the FN. The results and analysis were evaluated through manual calculations and found to be accurate, rational, and applicable to all mixture types, whether a tertiary stage was reached or not.

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Increased nighttime temperatures caused by retained heat in urban areas is a phenomenon known as the urban heat island (UHI) effect. Urbanization requires an increase in pavement surface area, which contributes to UHI as a result of unfavorable heat retention properties. In recent years, alternative pavement designs have become more common in an attempt to mitigate the environmental impacts of urbanization. Specifically, porous pavements are gaining popularity in the paving industry because of their attractive storm water mitigation and friction properties. However, little information regarding the thermal behavior of these materials is available. This paper explores the extent to which porous asphalt pavement influences pavement temperatures and investigates the impact on UHI by considering the diurnal temperature cycle. A one-dimensional pavement temperature model developed at Arizona State University was used to model surface temperatures of porous asphalt, traditional dense-graded asphalt, and portland cement concrete pavements. Scenarios included variations in pavement thickness, structure, and albedo. Thermal conductivity testing was performed on porous asphalt mixtures to obtain values for current and future analysis. In general, porous asphalt exhibited higher daytime surface temperatures than the other pavements because of the reduced thermal energy transfer from the surface to subsurface layers. However, porous asphalt showed the lowest nighttime temperatures compared with other materials with a similar or higher albedo. This trend can be attributed to the unique insulating properties of this material, which result from a high air void content. As anticipated, the outcome of this study indicated that pavement impact on UHI is a complex problem and that important interactions between influencing factors such as pavement thickness, structure, material type, and albedo must be considered.

a b s t r a c tEngineered pavements cover a large fraction of cities and offer significant potential for urban heat island mitigation. Though rapidly increasing research efforts have been devoted to the study of pavement materials, thermal interactions between buildings and the ambient environment are mostly neglected. In this study, numerical models featuring a realistic representation of building-environment thermal interactions, were applied to quantify the effect of pavements on the urban thermal environment at multiple scales. It was found that performance of pavements inside the canyon was largely determined by the canyon geometry. In a high-density residential area, modifying pavements had insignificant effect on the wall temperature and building energy consumption. At a regional scale, various pavement types were also found to have a limited cooling effect on land surface temperature and 2-m air temperature for metropolitan Phoenix. In the context of global climate change, the effect of pavement was evaluated in terms of the equivalent CO 2 emission. Equivalent CO 2 emission offset by reflective pavements in urban canyons was only about 13.9e46.6% of that without building canopies, depending on the canyon geometry. This study revealed the importance of building-environment thermal interactions in determining thermal conditions inside the urban canopy.

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