Experimental Study On Mechanical Properties Of High Ductile Concrete Under The Effect Of Low-Temperature Environment

China’s vast territory,a large part of the region belongs to the cold environment,to make the low-temperature environment of the concrete structure not damaged.it is neccssary to study and master the low-tempcraturc environment of the concrete structure damage evolution rules.To avoid the early retirement of concrete structures damaged by the low-temperature environment,it is imperative to further research new concrete with good frost resistance properties.In this papar,the basic mechanical properties of high ductille concrete(HDC for short)are found to be excellent under the action of a low-temperature environment.If HDC is applied to the engineering environment in cold areas such as alpine and dry cold,it can make concrete structures in low-temperature environments,avoiding diasters caused by the action of continuous low temperatures and reducing the loss of human resources,materials.and equipment,and capital.The paper has been studied for its anti-freezing performance by using the results of the subject group’s previous research on HDC mixes.The paper discusses the following aspects of HDC under the effect of sustained low temperature:(I)The test was carried out to test the mechanical properties of high ductile concrete under the action of three differem low-temperature environments by designing Group A(0℃).Group B(-10℃).and Group C(-20℃).firstly,the cubic strength,flexurla strength and splitting tensile strength were analyzed,and then the relationship between the three strengths was explored,the results showed that:the trend of compressive stregth flexural strength and splitting tensile strength of high ductile concrete show that the compressive strength,flexural strength and splitting tensile strength of high ductile concrete all tend to increase first and then decrease,and that the strength changes throughout the test process are greater at-10℃ and-20℃ compared to the compressive strength,flexural strength and splitting tensile strength at 0℃.The experimental data show that there is a proportional relationship between flexural strength.tensile strength.and compressive strength,and the strength decay model suitable for high ductile concrete under the action of low-temperature environment is proposed according to the data of this test.(2)The damage evolution rules of high ductile concrete under the action of the lowtemperature environment were investigated by the NMR technique,the pore structure,transverse relaxation time T2 of high ductile concrete under the action of the low-temperature environment were measured,the NMR T2 spectrum distribution,porosity,pore throat distribution,total area of T2 spectrum and other parameters of high ductile concrete under different low-temperature conditions were obtained,revealing the damage characteristics of HDC under the action of long-term low-temperature environment,providing a new method and idea for the application of service in concrete under continuous low-temperature environment.(3)Combining SEM techniques with NMR techniques to analyze the microstructural changes of high ductile concrete from the microscopic level,the results show that:HDC is internally dense with an initial porosity as low as 0.67%,with the increase of the continuous low-temperature action cycle,the internal pores of HDC will be filled with hydration products and become denser,and later on the porosity increases due to the internal stress of ice expansion and pore water pressure.The change in porosity also explains the change in the mechanical properties of HDC at the macroscopic level after it is subjected to the action of a sustained low-temperature environment.(4)Using uniaxial compression experiments on three types of high ductile concrete subjected to low-temperature environments using acoustic emission of concrete,we were able to determine the damage mechanism of the structure by accurately delineating the damage stages through qualitative analysis of the acoustic emission parameters.The experimental results show that the changes in the parameters of acoustic emission are used as a basis for the accurate qualitative classification of damage stages,and it is found that the changes in the parameters can,to a certain extent,reflect the internal damage development process of the material.The stress-strain curves of the HDC uniaxial compression tests were analyzed and a uniaxial compressive intrinsic model of the HDC was developed.The model fits the dimensionless stress-strain curve well,which provides a strong reference for the service of the HDC structure at low temperatures.