We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conduc...We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conductivity,and phloem and cambial ultrastructures of poplar.Overwintering death rates of poplar were not correlated with negative accumulated temperature or winter minimum temperature.Freeze–thaw cycles caused more bud damage than constant exposure to low temperatures.Resistance to freeze–thaw cycles differed among clones,and the budburst rate decreased with increasing exposure to freeze–thaw cycles.Cold-resistant clones had the lowest relative electrical conductivity.Chloroplasts exhibited the fastest and the most obvious reaction to freeze–thaw damage,whereas a single freeze–thaw cycle caused little damage to cambium ultrastructure.Several such cycles resulted in damage to plasma membranes,severe damage to organelles,dehydration of cells and cell death.We conclude that overwintering death of poplar is mainly attributed to the accumulation of effective freeze–thaw damage beyond the limits of freeze–thaw resistance.展开更多
It has been widely recognized that loess has a low stability and permeability,and it is susceptible to a sudden decrease in total volume or collapse upon wetting.When the railway subgrade was under the dynamic trainlo...It has been widely recognized that loess has a low stability and permeability,and it is susceptible to a sudden decrease in total volume or collapse upon wetting.When the railway subgrade was under the dynamic trainload,the loess subgrade was prone to instability and liquefaction.loess is higher than that of the cement modified loess,but lower than that of the MPG modified loess.However,the coefficient of permeability for the MPGcement modified loess has an opposite result,and the MPG-cement modified loess specimens have the best frost resistance.In addition,the mechanism of MPG-Bao Zhong railway is a key railway for Guyuan city,in Ningxia province of China,which is an important city of the Belt and Road.Due to the influence of largearea flood irrigation on the farmland,the subgrade had a degree of settlement.The settlement had not been alleviated after three treatments,which seriously affected the safety of the train.For this reason,cement,Modified Phospho Gypsum(MPG)and MPGcement were used to reinforce the subgrade loess,and the unconfined compressive strength test,permeability test and freeze-thaw cycle test were carried out.Then the compressive strength,impermeability and frost resistance of the three were analyzed and compared.The results indicate that the compressive strength of the MPG-cement modified cement modified loess is discussed.It is found that cement and MPG have two hydration reactions with water in loess.Ettringite,the hydration reaction product,which not only fills the pores,restricts the movement of the soil particles,but also acts as a connecting soil particle in the soil particles.Therefore,the strength of the modified loess continues to increase,and the physical properties of the modified loess are improved.展开更多
Through the fast freeze-thaw cycle test,accelerated carbonation test,and natural carbonation test,the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied.T...Through the fast freeze-thaw cycle test,accelerated carbonation test,and natural carbonation test,the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied.The experimental results indicate that freeze-thaw cycle apparently accelerates the process of concrete carbonation and carbonation deteriorates the freeze resistance of concrete.Under the combined action of freeze-thaw cycle and carbonation,the durability of lining concrete decreases.The carbonation depth of lining concrete at tunnel openings under freeze-thaw cycles and tunnel condition was predicted.For the high performance concrete with proposed mix ratio,the lining concrete tends to be unsafe because predicted carbonation depth exceeds the thickness of reinforced concrete protective coating.Adopting other measurements simultaneously to improve the durability of lining concrete at the tunnel openings is essential.展开更多
基金supported by grants from the National Key Research and Development Program of China(Grant No.2016YFD0600401)the Liaoning Provincial Key Research Project for Agriculture(Grant No.2015103002)
文摘We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conductivity,and phloem and cambial ultrastructures of poplar.Overwintering death rates of poplar were not correlated with negative accumulated temperature or winter minimum temperature.Freeze–thaw cycles caused more bud damage than constant exposure to low temperatures.Resistance to freeze–thaw cycles differed among clones,and the budburst rate decreased with increasing exposure to freeze–thaw cycles.Cold-resistant clones had the lowest relative electrical conductivity.Chloroplasts exhibited the fastest and the most obvious reaction to freeze–thaw damage,whereas a single freeze–thaw cycle caused little damage to cambium ultrastructure.Several such cycles resulted in damage to plasma membranes,severe damage to organelles,dehydration of cells and cell death.We conclude that overwintering death of poplar is mainly attributed to the accumulation of effective freeze–thaw damage beyond the limits of freeze–thaw resistance.
文摘It has been widely recognized that loess has a low stability and permeability,and it is susceptible to a sudden decrease in total volume or collapse upon wetting.When the railway subgrade was under the dynamic trainload,the loess subgrade was prone to instability and liquefaction.loess is higher than that of the cement modified loess,but lower than that of the MPG modified loess.However,the coefficient of permeability for the MPGcement modified loess has an opposite result,and the MPG-cement modified loess specimens have the best frost resistance.In addition,the mechanism of MPG-Bao Zhong railway is a key railway for Guyuan city,in Ningxia province of China,which is an important city of the Belt and Road.Due to the influence of largearea flood irrigation on the farmland,the subgrade had a degree of settlement.The settlement had not been alleviated after three treatments,which seriously affected the safety of the train.For this reason,cement,Modified Phospho Gypsum(MPG)and MPGcement were used to reinforce the subgrade loess,and the unconfined compressive strength test,permeability test and freeze-thaw cycle test were carried out.Then the compressive strength,impermeability and frost resistance of the three were analyzed and compared.The results indicate that the compressive strength of the MPG-cement modified cement modified loess is discussed.It is found that cement and MPG have two hydration reactions with water in loess.Ettringite,the hydration reaction product,which not only fills the pores,restricts the movement of the soil particles,but also acts as a connecting soil particle in the soil particles.Therefore,the strength of the modified loess continues to increase,and the physical properties of the modified loess are improved.
基金Funded by the National Key Basic Research and Development Plans-973 Plans(2009CB623203)the Key Project of National Natural Science Foundation of China(50739001)+1 种基金the National Natural Science Foundation of China (50878109)the Specialized Construct Fund for Taishan Scholars
文摘Through the fast freeze-thaw cycle test,accelerated carbonation test,and natural carbonation test,the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied.The experimental results indicate that freeze-thaw cycle apparently accelerates the process of concrete carbonation and carbonation deteriorates the freeze resistance of concrete.Under the combined action of freeze-thaw cycle and carbonation,the durability of lining concrete decreases.The carbonation depth of lining concrete at tunnel openings under freeze-thaw cycles and tunnel condition was predicted.For the high performance concrete with proposed mix ratio,the lining concrete tends to be unsafe because predicted carbonation depth exceeds the thickness of reinforced concrete protective coating.Adopting other measurements simultaneously to improve the durability of lining concrete at the tunnel openings is essential.
