Experimental Research On Gas Permeability Of Concrete Under The Coupling Effect Of High Temperature,High Humidity And High Pressure

The concrete containment of nuclear power plant will be affected by the coupling effect of high temperature,high humidity,and high pressure environment conditions in the event of a serious internal accident.Under these conditions,the containment still needs to maintain airtightness to prevent the leakage of radioactive gas.The gas permeability of concrete is closely related to environment conditions,but the existing related studies mostly focus on environment conditions such as temperature,humidity,and air pressure,without considering the coupling effects of multiple factors.In addition,there is currently no research on the gas permeability of concrete on the structural scale.Therefore,a prediction model is built for the gas permeability of concrete under the coupling effect of high temperature,high humidity and high pressure.A special test device is also designed and manufactured to conduct experimental research on the gas permeability of concrete specimens on the structural scale.In order to study the influence of environment factors on the gas permeability of concrete,7 test conditions were set with environment temperature,gas composition,and concrete strength as variables by applying a high temperature,high humidity and high pressure coupling environment consistent with the design of the working condition for 72 hours on one end of a cylindrical concrete specimen with a height of 1m and a diameter of 25 cm.The embedded temperature and resistivity sensors reflect the changes in the internal temperature field and moisture distribution of the specimens.Basing on the test result of the concrete cube compressive strength test,concrete moisture content and porosity test,concrete resistivity-water content calibration test,and gas permeability coefficient calibration test,the changes of gas permeability of concrete under the combined effect of high temperature,high humidity and high pressure is analyzed.The research indicates that:(1)The coupling effect of high temperature,high humidity and high pressure mainly affects the gas permeability of concrete by affecting the temperature and moisture distribution inside the concrete.The temperature in the area near the heating surface is relatively high,which leads to the evaporation of free water and the dehydration of combined water,and a low pore water saturation and relatively unobstructed gas permeation channel.The gas permeability coefficient can be more than 10 times that of normal status.As the distance from the heating surface increases,the temperature of concrete gradually decreases.When the temperature decreases to about 100°C,"moisture clog" phenomenon formed by the condensation of steam infiltrated in the high temperature zone,which will cause the pore water in this area to approach saturation,blocking the pore communication channel,so that the gas cannot penetrate further.(2)The penetration depth of gas in concrete is limited due to the influence of moisture clog under the coupling effect of high temperature,high humidity and high pressure.The maximum depth of gas penetration in concrete can be defined as the gas penetration depth of concrete which is equivalent to the distance between the critical saturation point caused by the moisture clog phenomenon and the heating surface.The gas penetration depth can be used as a design basis for the airtightness of concrete structures under high temperature,high humidity,and high pressure environments.(3)Under the effect of saturated high temperature,high humidity and high pressure gas,the gas penetration depth of concrete increases with the increase of environment temperature and water vapor partial pressure,and the longer the high temperature,high humidity and high pressure action time,the deeper the gas penetration depth.The gas penetration depth of the concrete can be predicted by the environment temperature and the partial pressure of water vapor.The gas penetration depth of concrete has an approximately linear relationship with the environment temperature.Within a certain gas pressure range,other gases except water vapor have no obvious influence on the gas penetration depth of the concrete.(4)The increase of concrete strength will reduce the gas permeability and gas penetration depth of concrete.