Experimental Study On Effective Pre-stressing Performance Of Concrete Under Ultralow Temperature

With the rapid development of economy,the environment is getting worse and worse,which forces people to pay attention to the living environment.It is urgent to develop clean energy such as natural gas.Prestressed concrete structure is widely used in liquefied natural gas storage tank,so it is very important to study its super low temperature effective preloading performance.In this paper,24 prestressed concrete specimens are made by using the experimental method.The effects of three key factors,namely,the initial preloading stress level,the ultra-low temperature and the moisture content of concrete,on the effective preloading performance of concrete at ultra-low temperature are discussed.The initial preloading stress level is 0.2、 0.4 and0.5,and the ultra-low temperature is-40℃、-80℃、-120℃ and-160℃.The water content of the concrete is treated with no water content of the prestressed test piece and soaked for 21 d.The test results show that with the decrease of low temperature,the loss of concrete pre pressure and axial deformation of prestressed specimens increase continuously,and the constant temperature time from the given ultra-low temperature to the temperature average point also increases gradually,and the loss of concrete pre pressure and axial deformation in this stage continue to develop;compare the four equal drop cooling ranges of 0℃ ～-40℃、-40℃～-80℃、-80℃ ～-120℃ and-120℃ ～-160℃,the loss of concrete preload is the largest in the cooling zone with the highest ultra-low temperature,but it decreases gradually with the decrease of low temperature,but its axial deformation has no obvious change trend;in the process of cooling to a given ultra-low temperature,the loss of concrete preload of different initial preload stress water level prestressed specimens shows different change characteristics.In the initial stage of cooling,the loss of concrete preload in the pre-stressed specimens with high initial pre compression stress level but without water soaking treatment is large,and vice versa,while the pre-stressed specimens with water soaking treatment are always at a low level;for the axial deformation difference between the pre-stressed specimens with different initial pre compression stress levels,the concrete moisture content has no obvious effect on it,but the axial recovery of the low initial pre-stressed specimens The shrinkage deformation is always greater than the high initial pre compression stress level;for various initial pre compression stress levels of pre-stressed specimens,the loss of concrete pre compression under different moisture content conditions increases with the decrease of low temperature.The loss of concrete preload is higher when the water content of high concrete is higher than that of low concrete when the initial stress level is low;the axial shrinkage deformation of prestressed specimens with different water content of concrete increases with the decrease of low temperature,but there are different characteristics in the cooling process.In addition,by comparing with the test results,it is shown that the finite element method for the effective preloading performance of concrete at ultra-low temperature given by the assumption and simplification is feasible to show the macro characteristics of the effective preloading performance of concrete at ultra-low temperature.The variation law of concrete super-low temperature preloading performance obtained in this paper can lay a foundation for further research in related fields,and also provide a basis for the structural design and safety performance evaluation of LNG tank concrete.