| Rain and snow weather in northern China often leads to snow and ice covering the pavement,which seriously affects road transportation capacity and usually induces traffic accidents.Traditional pavement snow removal and deicing methods all have their own limitations and shortcomings.Therefore,based on the phase change heat storage theory,phase change materials(PCM)was added into the asphalt pavement structure in order to form a pavement structure with phase change heat storage function,which can actively melt snow and ice in winter when it is rainy and snowy.Firstly,combining selection rules of PCM and technical performances of asphalt materials,the physical and chemical properties of PCM that can be used into asphalt pavement was studied.The polyethylene glycol was selected as the suitable PCM,which has suitable phase change temperature,excellent thermostability,good physical and chemical stability.The PCM was encapsulated by metal tubes and buried in the pavement structure.Then,based on the theory of thermodynamics and phase change heat storage theory,the finite element software Comsol was used to finish a numerical simulation about the temperature field of asphalt pavement structure in winter.After data collection of the winter temperature in Xi’an,the pavement structure temperature field after 3 years of annual temperature effecting was used as the initial temperature field of the numerical calculation,and the representative daily temperature change(Daily average temperature is 1℃,3 kinds of temperature range is 8℃,12℃,16℃and the pavement is covered with snow and ice)were selected as the temperature boundary condition of the calculation to improve the accuracy of the calculation.The typical asphalt pavement in Xi’an was generalized as the calculation model in order to analyze the temporal and spatial evolution of the temperature field of asphalt pavement structure under four working conditions.The metal tubes including PCM were buried into the asphalt pavement structure.The phase change energy storage asphalt pavement structure was used to analyze the influence of PCM on temperature change of pavement structure.The results show that: influence of the temperature difference between day and night on the temperature of ordinary asphalt pavement was about 0.35 m.The variation of road surface temperature was about 63% of the day-night temperature difference.The greater the temperature variation,the greater the temperature variation and spatial gradient of the pavement structure.The temperature in the pavement structure had a lag in the response to changes in air temperature.The greater the depth,the longer the lag time.The peak road surface temperature lagged behind the peak air temperature by about 1.3h,the node temperature at a depth of 0.04 m lags about 2.5h,and the node temperature at a depth of 0.1m lagged behind About 4.3h,the node temperature at the depth of 0.2m lagged about 7h;PCM asphalt pavement also followed this rule,and the closer the buried position of the metal pipe containing the phase change material was to the road surface,the more obvious the change in the temperature of the surrounding pavement structure;the metal pipe encapsulation with a diameter of 2cm and a horizontal spacing of 10 cm The temperature control effect range of PCM was about 2cm,and the temperature change range of the surrounding structure was within 1℃.Finally,the test method was used to analyze the temperature field change and snow melting capacity of the phase change energy storage asphalt pavement.The thermal cycle test results showed that when these 2cm diameter metal tubes containing PCM were set at a horizontal spacing of 2.5cm,the effect of PCM on the asphalt pavement surface structure was very obvious.The influence range was about 2cm,and the change range of temperature change is about 3℃.But the effect of PCM on the temperature of concrete base was very weak.The snow melting test results showed that the ice on the surface of the ordinary asphalt road interview piece only melted a small amount within 10 hours of the start of the test,its ice melting rate was about 10.2%.The ice on the surface of the PCM asphalt pavement interviewed part melted for 15 hours,its ice melting rate is about 43.5%.The ice melting speed rate of PCM asphalt pavement was about two times higher than that of ordinary pavement.These test results showed that when the ambient temperature fell below the solidification temperature of phase change materials,the phase change materials changed from liquid to solid phase,and the heat released can be used to melt snow and ice on the asphalt pavement.The phase change asphalt pavement showed better ability of melting ice and snow compared with ordinary asphalt pavement.When the phase change material was set on the surface layer,the phase change material can store and release energy in response to environmental temperature changing in time,and the effect of melting snow and ice will be better. |
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