Experimental Study On Basic Mechanical Properties Of Concrete Under Cryogenic Temperature

The rapid development of our society and the huge population base lead to huge energy demand.In recent years,acid rain,haze and other environmental pollution problems have attracted great attention.How to meet the energy demand without polluting the environment has become a hot research field at home and abroad.Natural gas with high calorific value and pollution-free combustion products has become a widely used fuel in China in recent years.In addition to being a fuel,natural gas is also an important chemical raw material.It plays an important role in chemical industry,medicine and environmental protection together with propane,ammonia and hydrogen.However,the biggest drawback of the above gaseous raw materials is that the large volume of the atmospheric gas state makes it difficult to transport and store large quantities of gases.Concrete has been widely used in liquefied gas storage tank structures such as liquefied natural gas(LNG)in recent years because of its excellent low temperature performance.However,the related research results are still few and scattered.Therefore,it is of great significance to study the performance of concrete in cryogenic temperature environment.This paper is a part of a series of research on ultralow temperature performance of concrete.195 prismatic specimens(100x100x300mm)and 263 cubic specimens(100x100x100mm)were made.The main influencing factors are cryogenic temperature,strength grade and water content of concrete.The moisture contents of specimens with C30,C40 and C50 concrete design strength grades were pretreated by soaking and baking without changing their internal pore structure and distribution.Compressive strength,splitting tensile strength,modulus of elasticity,peak strain and coefficient of thermal expansion for the concrete with different strength grades,moisture content(1.5% to 5.5%)and low temperature(-40? to-80?)were obtained by compressive strength test,splitting tensile strength test and temperature deformation test at cryogenic temperature respectively,and the corresponding expression were fit out.At the same time,the mechanisms of cryogenic temperature performance of concrete were also analyzed.The test results show that the compressive strength,splitting tensile strength,modulus of elasticity and peak strain of concrete at cryogenic temperature are significantly increased,and there is a clear linear relationship between them and concrete water content.The lower the concrete strength grade,the higher the concrete water content and the lower the imposed low temperature,the more obvious their increase.However,under the same conditions,the extent of improvement of several basic mechanical properties is different,and the changing regularities are different with the decrease of temperature.This is mainly due to the mechanism differences of these performance improvements.The variation of thermal expansion coefficient of concrete at cryogenic temperature is complicated.The thermal expansion coefficient of concrete with different strength grades varies with the decrease of imposed low temperature.C40 concrete decreases gradually with the decrease of imposed low temperature,while C50 rises first and then decreases.This is mainly due to the difference of meso-structure of concrete with different strength grades.The experimental results and the corresponding regression formulas for calculating the compressive strength,elastic modulus and splitting tensile strength of concrete at cryogenic temperature can provide a basis for compiling or revising relevant codes,designing these concrete structures such as liquefied gas storage tanks and evaluating their safety performance.