Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi

Nanning, China

Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi

Nanning, China

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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 | Liang J.,Guangxi University | Liang J.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | And 4 more authors.
Measurement: Journal of the International Measurement Confederation | Year: 2016

A new, simple apparatus was developed to measure the gas permeability of pervious concrete. The apparatus was assembled to allow gas flowing through the pervious concrete sample in a pressure-steady manner. A vacuum was used to create a stable gas flow through the sample while the gas-flowing rate was gauged by a Venturi tube. The gas permeability was measured under different applied pressures and different sample-saturated conditions. It is found that the permeability of pervious concrete decreases with the applied pressure gradient but does not obey the Klinkenberg effect. The saturated degrees do not distinctively influence the gas permeability of the pervious concrete. The gas permeability varies from 10-9 to 10-10 m2. This low permeability suggests that there is no buoyancy-driven convection inside the pervious pavements. This further implies that pervious pavements do not enhance the underlying root respiration and that the evaporation of the holding water in pervious pavements performs limited cooling effect. © 2015 Elsevier Ltd.


Yang H.,Guangxi University | Yang H.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | Deng Z.,Guangxi University | Deng Z.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | Ingham J.M.,University of Auckland
Construction and Building Materials | Year: 2016

Twelve beam tests were carried out in order to investigate the bond strength and bond position function between corroded rebar and recycled aggregate concrete (RAC), with the electrochemical method adopted to accelerate steel corrosion. Three recycled coarse aggregate (RCA) replacement percentages (i.e., 0%, 50% and 100%) and 4 expected corrosion crack widths of RAC (i.e., 0 mm, 0.05 mm, 0.3 mm, and 0.6 mm) were considered. Test data was used to calculate the bond stress along the anchorage length, and the influence of both RCA replacement percentages and the corrosion cracking widths on the bond strength and bond position function between the RAC and rebar. The bond position functions for different corrosion levels of reinforced RAC were also established. The results indicated that the ultimate bond strength of reinforced RAC beams decreased overall with an increase of the RCA replacement percentage and corrosion crack width, but that the rate of decline reduced with an increase of RCA and corrosion level. The bond position curve of the reinforced RAC beams was similar to that of natural aggregate concrete (NAC) beams subjected to bending and shear stresses before and after steel corrosion, with a sharp increase of the relative bond stiffness at both anchorage ends, and an almost linear decrease of relative bond stiffness in the range of 0.15–0.85 times the anchorage length. Increasing the RCA substitution rate had little effect on the bond position curves, and the bond distribution became more uniform as the crack widths increased. © 2016 Elsevier Ltd


Yang H.-F.,Guangxi University | Yang H.-F.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | Deng Z.-H.,Guangxi University | Deng Z.-H.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | And 2 more authors.
Gongcheng Lixue/Engineering Mechanics | Year: 2015

Experiment was carried out to study the influences of rebar corrosion ratios, recycled aggregate replacement ratios, and recycled concrete strengths on the bond-slip constitutive behavior of recycled concrete with corroded rebars. In order to obtain the curves of load-slippage between recycled concrete and different corrosions rebar as well as rebar strain along anchorage length, 23 specimens were investigated using pull-out test, in which a quick electricity method for rebar corrosion and inner-embedded strain foils approach were used in the laboratory test. Based on the experimental results, the bond stress and slippages along the anchorage length under different corrosions are calculated. The mechanisms of the stress transmission and bond position function difference, before and after rebar corrosion, are then analyzed. The bond position function and bond-slip constitutive model of corroded rebar and recycled concrete are proposed, which is expected to provide reference for finite element analysis. ©, 2015, Tsinghua University. All right reserved.


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
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 | Qin Y.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | Tan K.,Guangxi University | Tan K.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | And 3 more authors.
Cold Regions Science and Technology | Year: 2016

The construction of roadway embankments may destabilize the thermal stability of roadbeds in permafrost regions. One mitigating strategy is to face the embankment side slopes with a crushed-rock layer, which promotes convective cooling and cools the underlying permafrost. While research on the convective cooling of the crushed-rock layer is fairly plentiful, the solar absorption of this layer remains unknown in the current stage. Measuring the albedo of a crushed-rock layer is crucial to estimate the thermal performance of the roadway embankment. This study proposes the theory and procedure for measuring the albedo of crushed-rock layers. The albedo of crushed-rock layers with different sizes of aggregate is measured in sunny and cloudy weather. It was found that the albedo of crushed-rock layers decreases with the increase of the aggregate size. The reason for this correlation is that at a rough surface, some photons leaving the surface return to it, increasing its absorption. Incorporating light-colored aggregates on a highway surface or side slope layer may raise the highway albedo and cool the underlying permafrost. © 2016 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.


Yang H.,Guangxi University | Yang H.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | Qin Y.,Guangxi University | Qin Y.,Key Laboratory of Disaster Prevention and Engineering Safety of Guangxi | And 2 more authors.
Construction and Building Materials | Year: 2016

This paper studied the shear behavior of concrete with different levels of recycled coarse aggregate (i.e., 0%, 50% and 100%) after being subjected to different temperatures (i.e., 20°C, 200°C, 300°C and 400°C). Thirty-six beam specimens with uniform depth and varying width were designed to test their mechanical parameters including shear strength, peak shear strain, stress-strain curves and shear modulus. We analyze how these parameters are influenced by recycled coarse aggregate (RCA) content and by high temperature. We establish the shear stress-strain equations for RCA-embedded concrete after exposure to different temperatures. It is found that the aforementioned mechanical parameters are minimally influenced by the RCA content at ambient temperature (about 20°C). After exposure to high temperatures, the RCA content affects the shear strength insignificantly but increases the peak strain slightly. As the temperature elevates, the residual shear strength and shear modulus decline rapidly whereas the peak strain increases linearly. Furthermore, the normalized shear stress-strain curves become more disperse with the increment of temperature. © 2015 Elsevier Ltd. All rights reserved.


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.

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