Effect Of Water On Static And Dynamic Compressive Properties Of Concrete

Concrete structures usually work in the water environment,as a result the concrete is always saturated or semi-saturated.The compressive mechanical properties of wet concrete are significantly different from those of dry concrete,which may have negative influences on the structural safety.In this paper,the static,dynamic and fatigue compressive mechanical properties of wet concrete are studied respectively.The variation mechanism of mechanical properties of wet concrete are furtherly analyzed on the basis of experimental and simulated results.Following studies are conducted in this paper:(1)The compressive behavior of wet concrete under static loading was analyzed based on the mesoscopic numerical simulation,and the influence of pore and water content on the mechanical properties of concrete is clarified.(2)The dynamic properties of wet concrete subjected to seismic strain rate was numerically simulated on the basis of the mesoscopic model,and the effects of strain rate and water content on the dynamic performance were figure out.(3)The saturated concrete specimens were prepared by vacuum water-saturated equipment.Fatigue tests were carried out and the fatigue properties of dry and saturated concretes and concrete in the water environment were analyzed.(4)The internal water pressure in the precut crack of concrete under cyclic loading was tested,and the spatial and temporal distribution of internal water pressure were furtherly analyzed.The results can provide water pressure parameters for the fatigue numerical simulation of concrete with initial macro crackCertain decline on the static,dynamic and fatigue compressive strengths of wet concrete was found as compared with the dry concrete.The compressive strength of saturated concrete decreases nonlinearly with the increase of porosity,however the decreasing speed decreases.The elastic modulus of saturated concrete decreases linearly with the increase of porosity.The compressive strength and critical strain of concrete decrease linearly with the increase of pore water content.Under the condition of large porosity,the elastic modulus increases with the increase of pore moisture content.The dynamic compressive strength of concrete decreases linearly with the increase of pore water content,however the dynamic increase factor increases linearly with the increase of pore water content.A fitting formula to describe the compressive strength of concrete is proposed considering the effects of strain rate and pore water content.The damage growth rate of concrete increases and the fatigue life decreases in order of dry specimen,saturated specimen and specimen in water environment,which may lead to the fatigue life of concrete structure subjected to water environment can't reach the standard requirement.No matter whether the concrete specimen is water-containing,the peak strain and the residual strain have a three-stage relationship with the number of loading cycles.The strain rate at the second stage(the variation of peak strain between adjacent cycles)and the dissipation energy remain basically unchanged with the increase of loading cycles.A double logarithmic linear expression can be used to describe the relationship between the strain rate of stage two and the fatigue life,which is independent of the wet state of the specimen.A double logarithmic linear expression can also be adopted to relate the dissipation energy of stage two and the fatigue life,which depends on the wet state of the specimen.Therefore,the fatigue life of concrete can be predicted based on the strain rate or the dissipation energy of stage two.Under cyclic loading,the water pressure in the crack decreases from the crack tip to the opening direction and from the crack length center to the edge direction,and increases with the crack propagation.The water pressure in the crack increases linearly with the increase of crack depth and load amplitude,decreases with the increase of crack opening amount,and increases with the increasing load frequency.