Study On Dynamic Mechanical Properties Of Concrete In Different Pore Structure And Different Water Pressure Environment

In the seismic design of dam structures,the selection of the dynamic mechanical properties of concrete materials and their related parameters is one of the most important scientific issues in ensuring the seismic safety of dams and preventing seismic catastrophes.The seismic performance of dams in a water environment differs greatly from that in a dry atmospheric environment.Practice has shown that under strong seismic action,concrete dams can seriously crack and expand resulting in the loss of water retention capacity;on the other hand,due to long-term work in a water environment,the action of water pressure can cause large changes in the mechanical properties of concrete materials.Therefore,this project aims to investigate the factors affecting the dynamic mechanical properties of concrete in a pressurised water environment,and to analyse the effects of water pressure and strain rate on the dynamic properties of concrete from two perspectives: pore structure and loading path.The dynamic strength calculation model of concrete in pressurised water environment and the intrinsic structure model considering the pore structure parameters of concrete are further explored.The specific research content and main findings are summarised as follows.1)Based on the pore structure characteristics parameters of concrete net slurry with different amounts of fly ash air-entraining agent,the fractal dimension was calculated;the variation of the pore structure characteristics of the two types of concrete with the amount of admixture was analysed,the differences in the variation patterns of the two types of concrete were investigated,and the reasons for the differences were discussed.The study shows that the incorporation of both fly ash and air-entraining agent greatly reduces the proportion of harmful pores with a pore size greater than 200 nm in the concrete net pulp,introduces more micropores in the concrete net pulp,reduces the average pore size of concrete,and optimizes the internal pore size and distribution of concrete;the increase of fly ash incorporation decreases the concrete net pulp porosity,and the increase of air-entraining agent incorporation increases the concrete net pulp porosity.2)Based on the dynamic mechanical test data of concrete with different pore structures in pressurised water environment,the effects of three factors,namely pore structure,strain rate and water pressure,on the mechanical properties of concrete were investigated;a model for calculating the compressive strength of concrete considering two factors,namely water pressure and strain rate,was established,which can predict the dynamic compressive strength of concrete with different pore structures in pressurised water environment;based on this model,a sensitivity analysis of the A sensitivity analysis of concrete strength was carried out based on this model to investigate the extent to which the two factors of water pressure and strain rate affect the dynamic mechanical properties of concrete.It was found that the compressive strength of both air-entraining agent concrete and fly-ash concrete increased linearly with increasing strain rate;the sensitivity of air-entraining agent concrete to strain rate was stronger than that of fly-ash concrete in dry atmospheric conditions;the sensitivity of compressive strength of concrete with different pore structures to strain rate decreased with increasing water pressure.3)The Weibull-Lognormal principal structure model is improved,and the improved model has a higher correlation for fitting the dynamic stress-strain curve of concrete in a pressurised water environment.The correlation between the model parameters and the pore structure parameters is further discussed.The damage variables of concrete are defined based on the energy principle,and the dynamic damage mechanisms of concrete with different pore structures in a pressurised water environment are analysed from the perspective of damage development.It is shown that the mechanism of water influence on concrete damage development is complex,showing both a deterioration effect that promotes damage development and a water surrounding pressure effect that inhibits damage development.4)The effect of strain rate and cyclic loading on the dynamic damage characteristics of concrete was analysed based on dynamic compressive strength test data of concrete subjected to different cyclic loading effects in a 2 MPa pressurised water environment.The study showed that for the same number of cyclic loading,the slope of the stress-strain curve in the rising section of concrete decreased as the strain rate increased,the rate of concrete damage development decreased and the strain corresponding to the threshold value of concrete damage increased.5)Based on the test results,the damage development process of concrete in a pressurised water environment was investigated from the perspectives of both microscopic pore structure and macroscopic cyclic loading action,and the dynamic damage mechanism was further analysed.The study shows that the damage development rate of concrete slows down with the increase of strain rate,and slows down and then increases with the increase of cyclic loading action.