Low temperature cracking has become one of the important factors that diminish asphalt pavement's ride quality and service life.Especially in cold region,cracking caused by low temperature is the main distress for...Low temperature cracking has become one of the important factors that diminish asphalt pavement's ride quality and service life.Especially in cold region,cracking caused by low temperature is the main distress form.This paper discussed the effect of aggregate gradation on the low temperature performance in asphalt paving mixtures.A total of 11 asphalt mixtures with 11 different aggregate gradations and one asphalt binder content were studied.Volumetric properties of the coarse aggregate and asphalt mixtures showed aggregate grading has a significant impact on the degree of aggregate interlock in asphalt mixtures.A trend is existed in the low temperature performance with the change of gradation.With the aid of mathematic statistics,it indicates gradation affects the low temperature performance significantly.The findings also indicate the relationship between the degree of aggregate interlock in asphalt mixtures and the low temperature performance:With the stone-to-stone contact developed,the mixture has a high energy to resist contract and deformation at low temperature.The properties of fine aggregate and asphalt play an important part in resisting low temperature cracking in floating structure.But it provides lower energy to resist low temperature cracking compared to the skeleton structure.展开更多
Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamie triaxial tests with multi-stage eyelic loading process. The relationship betw...Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamie triaxial tests with multi-stage eyelic loading process. The relationship between dynamic shear stress and dynamic shear strain of frozen soil of subgrade under train loading and the influence of freezing temperatures on dynamic constitutive relation, dynamic shear modulus and damping ratio are observed in this study. Test results show that the dynamic constitutive relations of the frozen soils with different freezing temperatures comply with the hyperbolic model, in which model parameters a and b decrease with increasing freezing temperature. The dynamic shear modulus of the frozen soils decreases with increasing dynamic shear strains initially, followed by a relatively smooth attenuation tendency, whereas increases with decreasing freezing temperatures. The damping ratios decrease with decreasing freezing temperatures. Two linear functions are defined to express the linear relationships between dynamic shear modulus （damping ratio） and freezing temperature, respectively, in which corresponding linear coefficients are obtained through multiple regression analysis of test data.展开更多
To date,much of the research on green roof technology has focused on the capacity for these systems to contribute to the cooling of buildings during summer months.The thermal performance of green roofs in cold climate...To date,much of the research on green roof technology has focused on the capacity for these systems to contribute to the cooling of buildings during summer months.The thermal performance of green roofs in cold climate conditions is critical to understanding the potential of these roofs to decrease energy use in buildings during winter.This paper compares the behavior of two green roof systems with that of a conventional built-up roof by making use of a novel hot box testing apparatus.The green roofs tested are classified as extensive systems.Each system included:a 3 mm thick styrene butadiene rubber waterproofing membrane,0.2 mm thick polyethylene slip sheet,a 76 mm thick extruded polystyrene insulation layer,2 mm thick filter fabric,a 51 mm drainage layer followed by a 2 mm thick filter cloth,either 100 mm or 150 mm growing medium,and a 25 mm thick wild flower vegetated mat.The conventional roof consisted of a 2 mm thick layer of Kraft™vapour retarder bonded with insulation adhesive,51 mm of isocyanurate insulation,25 mm of fibreboard,a three ply(2 mm)cold-applied built-up roof membrane,and a gravel ballast finish 51 mm thick.Each roof was subjected to temperatures between 0℃ and–25℃,while the temperature within the hot box was held at 21℃.The effect of vegetation on a green roof to reduce wind speeds or increase snow cover were not considered in this study.The power required,as well as the temperatures throughout each system at steady state conditions,were monitored for 5 hours.The data collected from thermal testing suggests that the R-value of green roofs with 100 mm or 150 mm thick layers of growing medium is 37%higher than a conventional roof when subjected to temperatures of 0℃ to–25℃.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant No.50778057)the Research Fund for the Doctoral Program of Higher Education(Grant No.20060213002)
文摘Low temperature cracking has become one of the important factors that diminish asphalt pavement's ride quality and service life.Especially in cold region,cracking caused by low temperature is the main distress form.This paper discussed the effect of aggregate gradation on the low temperature performance in asphalt paving mixtures.A total of 11 asphalt mixtures with 11 different aggregate gradations and one asphalt binder content were studied.Volumetric properties of the coarse aggregate and asphalt mixtures showed aggregate grading has a significant impact on the degree of aggregate interlock in asphalt mixtures.A trend is existed in the low temperature performance with the change of gradation.With the aid of mathematic statistics,it indicates gradation affects the low temperature performance significantly.The findings also indicate the relationship between the degree of aggregate interlock in asphalt mixtures and the low temperature performance:With the stone-to-stone contact developed,the mixture has a high energy to resist contract and deformation at low temperature.The properties of fine aggregate and asphalt play an important part in resisting low temperature cracking in floating structure.But it provides lower energy to resist low temperature cracking compared to the skeleton structure.
基金supported by National 973 Project of China(No.2012CB026104)Undergraduate Training Programs for Innovation and Entrepreneurship of Heilongjiang(No.20140222038)+2 种基金Shen Hua Group Innovation Project(No.201212240384)National Natural Science Foundation of China(Nos.41430634,51174261,51078111)State Key Laboratory of Frozen Soils Engineering Open Foundation(No.SKLFSE201216)for which the authors are grateful
文摘Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamie triaxial tests with multi-stage eyelic loading process. The relationship between dynamic shear stress and dynamic shear strain of frozen soil of subgrade under train loading and the influence of freezing temperatures on dynamic constitutive relation, dynamic shear modulus and damping ratio are observed in this study. Test results show that the dynamic constitutive relations of the frozen soils with different freezing temperatures comply with the hyperbolic model, in which model parameters a and b decrease with increasing freezing temperature. The dynamic shear modulus of the frozen soils decreases with increasing dynamic shear strains initially, followed by a relatively smooth attenuation tendency, whereas increases with decreasing freezing temperatures. The damping ratios decrease with decreasing freezing temperatures. Two linear functions are defined to express the linear relationships between dynamic shear modulus （damping ratio） and freezing temperature, respectively, in which corresponding linear coefficients are obtained through multiple regression analysis of test data.
文摘To date,much of the research on green roof technology has focused on the capacity for these systems to contribute to the cooling of buildings during summer months.The thermal performance of green roofs in cold climate conditions is critical to understanding the potential of these roofs to decrease energy use in buildings during winter.This paper compares the behavior of two green roof systems with that of a conventional built-up roof by making use of a novel hot box testing apparatus.The green roofs tested are classified as extensive systems.Each system included:a 3 mm thick styrene butadiene rubber waterproofing membrane,0.2 mm thick polyethylene slip sheet,a 76 mm thick extruded polystyrene insulation layer,2 mm thick filter fabric,a 51 mm drainage layer followed by a 2 mm thick filter cloth,either 100 mm or 150 mm growing medium,and a 25 mm thick wild flower vegetated mat.The conventional roof consisted of a 2 mm thick layer of Kraft™vapour retarder bonded with insulation adhesive,51 mm of isocyanurate insulation,25 mm of fibreboard,a three ply(2 mm)cold-applied built-up roof membrane,and a gravel ballast finish 51 mm thick.Each roof was subjected to temperatures between 0℃ and–25℃,while the temperature within the hot box was held at 21℃.The effect of vegetation on a green roof to reduce wind speeds or increase snow cover were not considered in this study.The power required,as well as the temperatures throughout each system at steady state conditions,were monitored for 5 hours.The data collected from thermal testing suggests that the R-value of green roofs with 100 mm or 150 mm thick layers of growing medium is 37%higher than a conventional roof when subjected to temperatures of 0℃ to–25℃.
