| Tunnel structures are often subject to premature failure due to environmental factors and loads during long-term service.The failure of tunnel lining structure is mainly related to the damage of concrete material.Therefore,the improvement of the physico-mechanical properties and durability of concrete contributes to enhancing the stability and prolonging the service life of the lining structure,which is of great significance to the tunnel structure.Diatomite is a pozzolanic material.The use of diatomite as a cementitious material has the effect of improving the physico-mechanical properties and durability of concrete,so it has valuable prospects in the application of tunnel lining structure.However,the research on the damage evolution law of diatomite modified concrete(DMC)is relatively rare under the action of load and environmental factors.The damage evolution mechanism and acoustic emission(AE)characteristics of diatomite modified concrete are studied in this thesis.Firstly,SEM,MIP,XRD and TG are carried out to investigate the influence of diatomite on the microstructure and phase composition of concrete.Then,the fracture process of diatomite modified concrete(DMC)under uniaxial compression,three-point bending,sulfate attack and freeze-thaw is conducted by AE method.The influence of diatomite on the damage evolution law of concrete was analyzed,the damage evolution mechanism and AE characteristics of DMC were proved.The internal relationships among modification mechanism,mechanical properties,resistance to sulfuric acid corrosion,antifreeze properties and damage evolution of DMC were elucidated.In addition,the coupling relationship between AE parameters and DMC stress,strain and damage variables is investigated and The damage constitutive model of DMC was established considering the effects of multiple factors.Finally,a stress prediction model based on convolutional neural network(CNN)was constructed to realize the stress prediction of DMC with AE cumulative parameters.The main research contents and conclusions are as follows:(1)To reveal the modification mechanism of diatomite on concrete,the influence of diatomite content on concrete microstructure and phase composition was explored by means of SEM,MIP,XRD and TG.Then,the damage evolution mechanism and AE characteristics of DMC were studied under uniaxial compression.The influence of diatomite content on compressive properties of concrete and the damage evolution law of DMC were clarified.Based on AE parameters,the effects of diatomite on crack size and propagation mechanism of concrete are studied based on b value and fuzzy c clustering.The influence of diatomite on crack morphology of concrete is analyzed based on rise time(RA)and average frequency(AF)correlation analysis(RA-AF)and Gaussian Mixture Model.In addition,the influence of diatomite on the crack propagation mechanism of concrete is expounded from the point of phase transition by introducing the critical slowing down theory.At the same time,based on the critical slowing down theory,the AE monitoring failure warning model is established,which provides a new method to prevent concrete failure.The correlation between AE parameters,compressive strength and modification mechanism are summarized and analyzed.The quantitative relationship between AE parameters and compressive strength was established.The correlation between crack morphology and phase composition was clarified.(2)The damage evolution mechanism and AE characteristics of DMC were studied under the action of three-point bending.The effect of diatomite content on fracture property of concrete was analyzed.The DMC fracture damage model was established based on Weibull theory and AE energy data.The fracture damage evolution law of DMC were quantitatively described,and the inhibition effect of diatomite on the development of concrete damage was clarified.By analyzing AE amplitude and statistics,the variation rules of b value and entropy value were obtained,the fracture scale characteristics of DMC were quantitatively revealed.Meanwhile,the correlation between b value and entropy value was discussed.Multifractal detrended fluctuation analysis is introduced based on AE amplitude data.The multi-scale characteristics of DMC fracture behavior are described quantitatively by analyzing the timevarying law of multi-fractal parameters,which further proves that diatomite inhibits the fracture scale of concrete.The cracking damage behavior and cracking resistance mechanism of DMC were revealed from the macro and micro scale,and the quantitative relationship between multifractal parameters and fracture toughness was obtained(3)The damage evolution mechanism and AE characteristics of DMC under uniaxial compression were studied after sulfate corrosion.The effect of diatomite on sulfate corrosion resistance of concrete was quantitatively evaluated from the view of physical and mechanical deterioration,and the relationship between AE information and damage evolution law was explored.The ratio of peak value of AE count rate in elastic stage and plastic stage is used as the quantitative index of initial damage degree of concrete to obtain the initial damage value of modified concrete with different dosage of diatomite.It is found that 3% diatomite has the most obvious improvement on sulfate corrosion resistance of concrete,which is consistent with the evaluation results of physical and mechanical indexes.The mechanism of sulfate corrosion resistance of diatomite to concrete is revealed from microstructure and material composition.The quantitative relationship between cumulative and compressive strength of DMC was found.(4)The damage evolution mechanism and AE characteristics of DMC under uniaxial compression were studied after freeze-thaw action.The influence of diatomite on the deterioration law of physical and mechanical properties of concrete was compared and analyzed under freeze-thaw action.Based on the deterioration trend of the relative dynamic elastic modulus,the evolution model of compressive strength under freeze-thaw cycle was proposed.The rationality of the model was verified by the test data.The AE parameters variation characteristics of DMC under freeze-thaw cycle were analyzed,the damage evolution law of DMC was explored.It is found that the variation trend of cumulative under freeze-thaw cycle is consistent with the deterioration law of physical and mechanical properties,which provides an important reference for evaluating the frost resistance of DMC based on AE parameters.(5)On the basis of the above research,the coupling relationship between AE cumulative count and stress and strain of DMC under uniaxial compression was analyzed,and the functional relationship between AE parameters and damage variables was explored.The DMC damage constitutive model was established considering the dosage of diatomite,environmental factors and load.The model was verified to be accurate through the test data,and the damage evolution behavior of DMC could be reasonably reflected through the model.In addition,the stress prediction model is built by combining CNN and AE data.This model can accurately predict the stress received by concrete based on the cumulative AE parameters.Compared with the neural network model(ANN),this model has higher accuracy. |
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