Experimental Study On Initial Damage And Mechanical Properties Of Concrete In High-Altitude Areas

The high-altitude areas in the west are cold and have special climatic conditions.Due to the high altitude and low air pressure,forming concrete in this environment will cause damage and destruction such as increased concrete pores,difficult and insufficient air entrainment,and uneven distribution of aggregate mortar.In order to study the influence of high altitude and low air pressure factors on the performance of concrete,the sulphoaluminate cement concrete with different admixtures was vibrated in a low air pressure environment.Compressive strength and split tensile strength were used as the mechanical evaluation indexes to characterize the concrete performance.The law of changes in mechanical properties.The freeze-thaw cycle test is used as the durability evaluation index to characterize the changing law of the durability of concrete.The elastic wave velocity is used to perform macroscopic quantitative characterization of concrete damage;the panoramic bubble microcrack quantitative analysis system is used to quantitatively characterize concrete damage from a microscopic point of view.The main conclusions are as follows:(1)The compressive strength of concrete after vibrating in low air pressure environment is lower than that of concrete vibrated under normal pressure.And the higher the content of air-entraining agent,the more obvious the decrease of concrete compressive strength.The compressive strength of long-term low-pressure vibrating is lower than that of short-term vibrating,but the degree of decrease is not obvious.The split tensile strength law is similar to the compressive strength.After the concrete is mixed with air-entraining agent,the initial value of its compressive strength decreases.The greater the air content,the greater the degree of decrease in compressive strength.The compressive strength of concrete is the basis of many design codes.The amount of air-entraining agent and the type of admixture should be properly selected in the actual project.(2)The frost resistance of concrete with the same mix ratio and the same amount of admixtures after vibrating in a low-pressure environment is weaker than that under normal pressure.With the increase of vibrating time in a low-pressure environment,the frost resistance of concrete decreases.When vibrating concrete in a low-pressure environment,compared with microcapsule admixtures,new admixture 3#,admixture4#,the frost resistance of concrete added with traditional air-entraining agent and new admixture 2# has been significantly improved.(3)Elastic wave test shows that low-pressure environment vibration increases the initial damage of concrete.When the external conditions are the same,as the amount of air-entraining agent increases,the degree of concrete damage also increases.The vibrating time under low air pressure has little effect on the initial damage degree of concrete.The sum of bubble area and average bubble diameter of concrete slices can quantitatively characterize the damage of concrete and reflect its frost resistance.