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Qin Y.,Guangxi University | Qin Y.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi
Renewable and Sustainable Energy Reviews | Year: 2015

Abstract Conventional impervious pavements have dark surface and large thermal inertia. During summertime they tend to absorb and store solar radiation but negate the evaporative cooling, contributing to the development of urban heat island (UHI). The idea of using cool pavements to mitigate the UHI has gained momentum recently. This review synthesizes the existing definition, physical mechanism, and typical cooling techniques of cool pavements, presenting the influence of cool pavements on the urban thermal environment. Benefits, penalties, costs and policies for the applications of cool pavements are presented with special emphasis on reflective pavements and evaporative pavements. The review suggests that the definition of cool pavements remain incomplete; that the influence of cool pavements on the air temperature in the urban canopy layer is unknown; and that the impact of cool pavements on the thermal conditions of adjacent buildings and pedestrians remains unknown. Many speculations of using cool pavements to battle the UHI effect need refinements and validations. Heat-harvesting pavements seem interesting because they not only stay cool but harness renewable energy. However, the results from the heat-harvesting pavement prototype require scrutiny on the power output, durability, and lifetime of the pavement system. Future studies are expected to understanding the impacts of cool pavements on pedestrian thermal stress, on adjacent building's energy loads, and on the air temperature in the urban canopy layer. © 2015 Elsevier Ltd


Qin Y.,Guangxi University | Qin Y.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi
Energy and Buildings | Year: 2015

Abstract Solar irradiance to an urban canyon is subjected to multiple reflections, a process that increases solar absorption and contributes to the unban heat island. The absorption depends on the urban structures, and the day of the year, and the albedos of the walls and pavement. This study develops a numerical model to predict the urban canyon albedo (UCA) and validates the model with experimental observations. It estimates whether increasing the pavement albedo can raise the UCA effectively. It evaluates the reflective diffuse radiation from the pavement to adjacent building walls. It is found the ratio of building's height to the road's width, or called the aspect ratio, controls the UCA while other factors play secondary roles. Reflective pavements in an urban canyon reflect a sizable additional diffuse radiation to the adjacent walls during summertime. It is recommended that reflective pavements can be used only if an urban canyon has an aspect ratio no greater than 1.0. © 2015 Elsevier B.V. All rights reserved.


Qin Y.,Guangxi University | Qin Y.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi
International Journal of Heat and Mass Transfer | Year: 2016

Pavement surface temperature is critical to the pavement performance and the development of cool pavements. The variations of the pavement surface temperature have been documented in numerous empirical models. These models, however, exclude critical parameters like albedo and thermal inertia but include many empirical parameters that have no thermo-physical meanings. This study presents a theoretical model to predict the surface temperature of pavements and validates it against field data and numerical results from the existing studies. It is found that the amplitude, maximum, and minimum of the pavement surface temperature increase linearly with the pavement surface absorptivity, the daily-zenith incident solar irradiation, and the reciprocal thermal inertia. Among these, raising the pavement albedo is more effective to reduce the pavement surface temperature than increasing the pavement thermal inertia. The model has practical meanings to predicting the maximum, minimum, and amplitude of the pavement surface temperature and to developing cool pavements. © 2016 Elsevier Ltd. All rights reserved.


Qin Y.,Guangxi University | Tan K.,Guangxi University | Tan K.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | Liang J.,Guangxi University
Cold Regions Science and Technology | Year: 2015

Roadway embankments over permafrost stratum are susceptible to thawing damage. Installing shading boards on the embankment side slope reflects solar irradiance back to the sky and thus has been deemed as a roadbed cooling technique. Research on the cooling effect of shading boards has centered on the temperature evolution of the roadbed under the board and on the optimum design of the board. Few researches, however, have been dedicated to understand the heat balance between the board and the embankment and to adapt the board's thermal properties to maximize the cooling effect. This study models the heat flux balance between the board and the embankment side slope and validates the model with measured data logged from an in situ shading board experiment. The validation of the model reveals that shading boards with smaller lower-surface thermal emissivity perform stronger cooling effect. Further outdoor experiments are expected to paint the shading board upper surface with differential albedo to understand the influence of board albedo on the cooling effect. © 2015 Elsevier B.V.


Qin Y.,Guangxi University | Qin Y.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | Yang H.,Guangxi University | Yang H.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi
Construction and Building Materials | Year: 2015

Recycled concrete aggregate (RCA) is being encouraged to use as substitute materials of the virgin aggregate for the pavement materials. RCA used in road layers is submitted to intermittent leaching. The leachant neutralizes the alkali of the RCA and the leaching intermission promotes the carbonation of the RCA's residual mortar. Both processes introduce acid to the RCA, releasing the pH-dependent toxic constituents of the RCA to the local aquifer. In this study, the acid intake caused by the leachant renewal and leachate decantation is calculated and compared with the acid intake induced by the carbonation during the leaching intermission. It is found that carbonation dominates the acid intake of the leached RCA layer while the renewal-decantation process acts only secondary role. The use of open-graded RCA base overlain by a dense pavement is recommended to reduce the carbonation rate of the RCA and to retard the leaching pH-dependent toxic elements to the local aquifer. © 2015 Elsevier Ltd. All rights reserved.

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