Research On Engineering Service Life Of Concrete Material For Highway Bridge

The formation of the qinghai-tibet plateau permafrost is mainly due to its high altitude,the distribution characteristics of low latitudes in the region caused by the sun radiation intensity and even higher than that of most areas in China,in addition to road construction is bound to damage the surface of the original state of thermal equilibrium,on the surface heat especially large black asphalt pavement section.At the same time,the impact of global warming on the Qinghai-Tibet Plateau is becoming more and more serious,and the thickness of the active layer in the permafrost area is increasing year by year,which puts forward higher requirements for road construction in the permafrost area and maintaining the stability of the existing road through the permafrost area for a long time.On qinghai-tibet plateau highway G109 naqu to yushu on-site,longitudinal crack,heat pipe thermal erosion and slope instability after thermal damage investigation,it is concluded that the fundamental reason lies in the permafrost region,wide range of expressway asphalt pavement thermal equilibrium state of the original state of permafrost soil vulnerable to the effects of ambient heat,causing the freezing and thawing behavior of the upper permafrost active layer,As a result,the frozen soil foundation loses the strength and structural stability of the original frozen state,and under the self-weight of the roadbed and the long-term load of vehicles,the uneven structural deformation gradually accumulates,which eventually leads to the instability of the roadbed structure and the hydrothermal damage of the asphalt pavement.At present,passive measures of heat insulation and cooling,such as ventilation pipe subgrade,heat exhaust of heat pipe,EPS heat insulation board and block rock subgrade,can only relieve heat invasion during pavement heat absorption period to a certain extent.Therefore,active intervention of wide subgrade temperature in high altitude permafrost area has broad application prospects.The following research works are carried out on the design of active refrigeration temperature control for permafrost subgrade.(1)By deducing the basic calculation formula of unsteady heat conduction,a test method suitable for simultaneous determination of thermal parameters in negative temperature domain and the development of supporting test equipment are proposed.The design of the thermal parameter test of permafrost on the Qinghai-Tibet Plateau and the analysis of the variation among the influencing factors related to the parameters were carried out to determine the reference value ranges of specific heat capacity and thermal conductivity under different soil sample types,water content and negative temperature domain conditions,so as to provide a basis for the analysis of the heat transfer and distribution rules of the permafrost roadbed during the pavement heat absorption period.At the same time,the simulation analysis of refrigeration system heat removal effect in frozen soil provides a foundation.(2)By analyzing the working principles of two types of active refrigeration and developing the corresponding refrigeration test equipment,the finite element method was used to simulate the cooling radius and heat dissipation efficiency of the single cooling pipe in the permafrost,and then the configuration design of the cooling coil was carried out to meet the annual zero heat input of the permafrost active layer within the road area.Combined with the year-round measured data of the broad roadbed on the Qinghai-Tibet Plateau,the dynamic cooling rate requirements of the cooling end are calculated.Finite element simulation based on frozen soil refrigeration experiment was carried out and the temperature control indexes of the two active refrigeration methods under the condition of heat removal efficiency were given,which provided reference indexes for the subsequent design of refrigeration schemes and energy efficiency evaluation.(3)The calculation formula of superimposed temperature field which takes the width of subgrade bottom and the temperature gradient inside and outside as parameters,carries out the heat transfer statistics of subgrade bottom at different depths,and determines the total demand of refrigeration pipeline layout according to the cumulative heat transfer amount of pavement in the heat absorption period.According to the temperature lateral distribution state of the temperature control surface depth,the distribution principle of the refrigeration pipeline along the base width is determined,and the design of the full-width refrigeration scheme of the wide roadbed based on heat transfer control is finally formed.