Study On The Relationship Between Temperature History And Short-term Creep Properties Of Cement Mortar

Process the prepared test specimens of cement mortar: divide the test specimens of cement mortar into five groups and bake them at 100?,150?,200?,250? and 300? respectively.Keep them sealed after baking and wait for their natural cooling to room temperature to have creep tests.Select the load stress level which is suitable for the study of creep damage of cement mortar,have uniaxial compression creep tests to the five groups of test specimens of cement mortar with different temperature history using the SAW-2000 microcomputer control electro-hydraulic servo rock triaxial pressure testing machine to get the creep test curve of the cement mortar with different temperature history.And also analyze the creep amount,the creep ratio,the creep rate and the creep stiffness modulus of the creep test curve.Fit the test data and get the creep model parameters and their variation laws in different temperature history with the Nishihara model.Have a numerical simulation of the uniaxial compression creep of cement mortar with different temperature history with FLAC3 D numerical analysis software and compare the numerical simulation results with the experimental results.Then discuss the relationship between temperature history and creep properties of cement mortar.The results of the study are as follows:The axial creep test curves of cement mortar with different temperature history are the same basically and they all include three stages of creep failure process: transient creep stage,stable creep stage and accelerated creep stage.The creep compaction stage of the axial creep test curve of cement mortar after different temperature history treatment is more obvious.It is indicated that the internal moisture of cement mortar is evaporated and lost after baking at high temperature,there are gaps in the internal structure to increase the porosity of the cement mortar.This shows that high temperature will reduce the compactness of cement mortar.The creep amount,the creep ratio,the creep rate and the creep stiffness modulus are negatively correlated with the temperature history of cement mortar when the load stress level is the same.Among them,the creep amount decreased by 14.3%,31.6%,10.3% and 42.3% with the increase of temperature history.The creep ratio decreased by 25.5%,47.1%,20.3% and 25.1% respectively.It is indicated that the internal hydrate of cement mortar is decomposed after baking at high temperature and the degree of adhesion between the components is reduced.The relationship between the components becomes smaller with the temperature history increases.So the plasticity of cement mortar decreases gradually and the brittleness of cement mortar increases gradually.The creep rate decreased by 47.9%,13.7%,36.8% and 83.7% with the increase of temperature history.It is indicated that the ability of cement mortar to resist deformation increases gradually with the increase of temperature history.The creep stiffness modulus decreased by 8.1%,40.2%,9.2% and 8.6% with the increase of temperature history and it is indicated that the creep strain of cement mortar decreases gradually with the increase of temperature history.The results show that the temperature history can inhibit the creep of cement mortar and the creep property decreases with the increase of temperature history based on the analysis of four important parameters related to creep property which are creep amount,creep radio,creep rate and creep stiffness modulus.The creep constitutive relationship of cement mortar with different temperature history is described with Nishihara model.The results show that elastic modulus of cement mortar is inversely proportional to temperature history,so the stiffness of cement mortar decreases with the increase of temperature history;the viscoelastic modulus and viscous coefficient of cement mortar are inversely proportional to the temperature history,so the viscosity of cement mortar decreases gradually;the viscoplasticity coefficient of cement mortar is inversely proportional to temperature history so the plasticity of cement mortar decreases gradually;the relaxation time of cement mortar is proportional to the temperature history,so the resistance to permanent deformation of cement mortar increases gradually.Have a numerical simulation of the uniaxial compression creep of cement mortar with different temperature history with FLAC3 D numerical analysis software and compare the numerical simulation results with the experimental results.The results show that the variation trend of the creep curves obtained in the simulation are basically consistent with those obtained in the experiment;the creep amounts and the creep rates obtained in the simulation are also consistent with those in the experiment and the difference is small.The results of the comparison show that FLAC3 D can not only simulated the entire uniaxial compression creep test well,but also reflect the relationship between temperature history and creep mechanical properties of cement mortar.