Study On Short-Time Creep Characteristics Of Rock-Like Materials Under Different Moisture Content

In this paper,the creep properties of rock-like materials with different moisture content are studied by using cement mortar and combined with its creep mechanical property,the relationship between moisture content and creep mechanical properties of cement mortar is studied macroscopically and microscopically.In this paper,the prepared cement mortar test pieces were firstly treated,after dried,the test pieces were divided into 6 groups.These 6 groups of test pieces were immersed for different time respectively to generate different moisture contents.Then the test pieces were weighed and sealed for storage.The loading grade was decided by the uniaxial compression test.Each loading lasted 2h.And if the test piece was not damaged within 2MPa,the SAW-2000 microcomputer controlled electro-hydraulic servo rock tri-axial tester was used to carry out a uniaxial compression creep test on the 6 groups of cement mortar test pieces containing different moisture content.A creep test curve was obtained accordingly,and the creep curve was analyzed in terms of value,ratio,rate,and stiffness modulus.A microscopic and macroscopic morphological analysis was conducted on the fractured test pieces obtained by the uniaxial compression test using a transflective polarizing microscope.According to the results of uniaxial compression creep test,the Burgers model was chosen to fit the test data,which could obtain the influence of moisture content on the creep model parameters of cement mortar and its change law and decide the effect of different moisture content on the creep constitutive relation of cement mortar.The creep constitutive relation parameters were verified by the FLAC3D software.The results of the test indicated that:?1?By the macroscopic and mesoscopic observation of test piece damaged by uniaxial compression creep test,under an action of continuous load,the test piece was found to have a very obvious phenomenon of crush-crisp,and the unevenness inside the cement mortar resulted in the presence of many weak surfaces inside the cement mortar.Under the action of long-term continuous load,the original weak surfaces were developed continuously,and cracks were produced throughout the whole test piece,resulting in fracture of the test piece.?2?The roughness of main fracture surface of the concrete gradually decreases with the increase of moisture content,suggesting that the moisture inside the test piece will promote the internal hydration reaction,which contributes to the creep damage of the test piece.With the decrease of moisture content,the fractal dimension decreases by 1.45%,-0.27%,0.80%,1.05%,1.03%when the moisture content is increased by 100 times,decreases by 1.08%,0.93%,1.28%,1.05%,1.61%when the moisture content is increased by 400 times,and decreases by 1.08%,0.93%,1.28%,1.05%,1.61%when the moisture content is increased by 600 times.On the mesoscopic level,it was confirmed that the moisture content reduced the brittleness of cement mortar test piece.?3?The creep test curves of cement mortar test piece with different moisture content obtained by uniaxial compression creep test were basically the consistent,which included the three phases of creep completely,namely,the initial creep phase,stable creep phase and accelerated creep phase.?4?According to the analysis of the results of uniaxial graded loading creep test,when the loading grade was the same,the creep value,creep ratio and creep rateare all positively correlated with the moisture content of cement mortar,while the stiffness modulus are negatively correlated.With decrease of moisture content,the creep strain decreased 30.68%,52.41%,39.76%,34.22%,40.15%,and the creep ratio decreased3.97%,12.28%,10.39%,44.23%,36.25%.Among them,the creep value and creep ratio of cement mortar increased as moisture content increased,suggesting that the internal pore moisture content of the cement mortar was increased as a result of immersion,which lubricated the components of the cement mortar,and resulted in a lowered caking ability between various components.And as the moisture content increasing,the connection between the components becomes less and less,which resulting in an increase in the plasticity of the cement mortar test piece,and a decrease in brittleness.Under the first preset load,the creep rate decreases by 82.21%,40.15%,46,13%,61.05%and 46.24%with the decrease of moisture content,which indicates that as the moisture content increasing,the ability of cement mortar to resist deformation gradually decreases.The creep stiffness modulus decreases with the increase of moisture content.Through the analysis of four key parameters related to creep property,that is,the creep value,creep ratio,creep rate and creep stiffness modulus,it is shown that the moisture content contributes to the creep of cement mortar,and as the moisture content increasing,the creep property is gradually enhanced.?5?The results of uniaxial graded loading creep test were analyzed,suggesting that,when the moisture content remained the same,the creep value,creep ratio and creep rate tended to firstly decrease and then increase with the increase of loading gradewhich indicates the ability of cement mortar test piece to resist transient plastic deformation was enhanced.In other words,it exhibited a phenomenon of hardening firstly,and as the loading grade continued to rise,a phenomenon of softening appeared.?6?According to the results of uniaxial grading loading creep test,the Burgers model was chosen to fit the data of the creep constitutive relation of cement mortar test piece containing different moisture content.When the loading level remained the same,as the moisture content increased,the elastic viscosity parameters of the Burgers model showed a regular change:the elastic modulus of cement mortar was inversely proportional to the moisture content,indicating that the stiffness of cement mortar tended to decrease with the increase of moisture content;the viscosity coefficient of cement mortar was inversely proportional to the moisture content,which also indicated that the viscosity of cement mortar decreased.At the same time,the Burgers model was simulated by FLAC^3D software,which proved that its parameters were verified.