Study On Dynamic Mechanical Properties Of Concrete With Different Pore Structure Characteristics In Hydraulic Environment

Concrete used to build dams and sea-crossing bridges is perennially under high water pressure.In water,concrete at different heights is subjected to different water pressures,which leads to different water content of concrete.Under dynamic loads,water content has a greater impact on the dynamic mechanical properties of concrete.As a porous medium material,the pore structure characteristics of concrete will seriously affect the water content of concrete.Therefore,in order to study the dynamic performance of concrete under water pressure,it is necessary to consider the pore structure characteristics of concrete.Therefore,in the pressurized water environment,considering the characteristics of internal pore structure and water content,the study of dynamic mechanical properties of concrete has become the guiding ideology to establish the research contents and objectives of this paper.The purpose of this paper is to explore the dynamic characteristics of concrete in different pressurized water environments by taking the pore structure characteristics of concrete as a key factor.Therefore,concrete specimens with different pore structure characteristics?F00,F20 and F40 respectively represent three different pore structure characteristics?are obtained by mixing different content of fly ash?0%,20%,40%?.Uniaxial compression tests are carried out under different water pressures?drying,1 MPa,3 MPa,5 MPa?and different strain rates(10^-5/s,10^-4/s,10^-3/s,10^-2/s).Proven.Before uniaxial compression test,water saturation pretreatment was carried out on the specimens in pressurized water environment;and the correlation between water content characteristic value and concrete water content was established by using water content characteristic value calculation theory;on this basis,the correlation between water content characteristic value and concrete dynamic characteristics was established;furthermore,the relationship between dynamic mechanical properties of concrete and pore structure,water content was explored.Finally,the damage and failure mechanism of concrete are analyzed.The specific contents and main conclusions of this paper are as follows.?1?In the aspect of pore structure characteristics of concrete:By summarizing and analyzing some scholars'research on pore structure characteristics of fly ash concrete,the influence of fly ash on mechanical properties of concrete is explored.The research shows that the addition of fly ash fills the internal pore of concrete and makes it more compact.With the increase of fly ash,the volume porosity of concrete decreases first and then increases.When the content of fly ash is 10%,the volume porosity of concrete reaches the lowest.?2?In the aspect of water content research,several methods of concrete water content measurement are compared and analyzed,and the characteristic value of water content is defined to represent the amount of water content in concrete,and the characteristic value of water content under different pore structure characteristics is obtained.The relationship among the characteristic value of concrete water content,water pressure and pore structure characteristics is established.The results show that under the same water pressure,the characteristic value of water content of F00 concrete is the largest,followed by F40concrete and F20 concrete.The main factors affecting the water content of concrete with different pore structure characteristics are the porosity of coarse and fine pore,which has little relationship with the porosity of capillary pore.?3?In the aspect of dynamic compressive strength of concrete,under certain confining pressure of water,saturated concrete is treated,and uniaxial compressive tests at different loading rates are carried out to obtain the relationship between compressive strength,dynamic reinforcement factor and strain rate of concrete.The relationship between water content per unit volume,dynamic compressive strength and strain rate of concrete is established.The results show that there is a threshold of water content under dynamic loading.When water content is less than this threshold,the peak stress of concrete decreases with the increase of water content,and the rate effect of concrete with different pore structure characteristics is similar.The ratio of force added value to water content characteristic value and strain rate is quadratic function,while the ratio of F40 and F00concrete is linear function.The effect of water on concrete strength is twofold.On the one hand,water weakens the strength of concrete,on the other hand,under dynamic load,water strengthens the strength of concrete.The two functions are superimposed and macroscopical.The effect of water on the strength of concrete is also enhanced with the increase of loading rate.?4?In the construction of stress-strain constitutive model:In order to explore the damage characteristics of concrete with different pore structure characteristics,Weibull-Lognormal model is selected to fit the stress-strain curve of concrete,and the damage development curves under different strain rates are obtained.The research shows that Weibull-Lognormal fits the stress-strain curve well under this working condition.The increase of water confining pressure will delay the damage development of concrete,and F20 concrete is most sensitive to confining pressure effect.