Influence Of Free Water On Concrete Mechanical Properties Under Dynamic Load

Many concrete structures are often located in the water,such as dams and railroad tracks in rainy regions.The free water in environment could penetrate into concrete due to water pressure and capillary effect,resulting in a wet concrete.Concrete structures working in the water environment suffer not only static loads but also dynamic loads such as earthquake,impact,and explosion during their service life.To reveal the damage mechanism of concrete in water environment under dynamic loads,the concrete specimens with different water saturations?0%,50%and 100%?were prepared rapidly by a vacuum saturating method.Then,the mechanical properties of concretes under different loading rates(10^-5s^-1,10^-4s^-1,10^-3s^-1 and10²s^-1)were tested to explore the influence of pore fluid viscosity on the mechanical properties of concrete,and to analyze the change mechanism of rate effect of wet concrete.The main achievements of this study are listed as follows:?1?The vacuum saturating method can saturate the concrete specimens rapidly.The CT results show that the free water distributed evenly in the concrete and the porosity of the concrete does not changed before and after the vacuum saturating.Therefore,vacuum saturating method is more effective to experimentally reveal the effect of water on the mechanical properties of concrete.?2?The strength of concrete decreases with increasing saturation of pore water,regardless of whether it is under quasi-static or dynamic loading condition.Both dry and saturated concretes have a strain rate effect,however the saturated concrete is significantly sensitive on the loading rate.Compared with previous experiments,this results in this paper show that the vacuum saturating method can remove the influence of other factors such as secondary hydration of concrete on the test results.?3?The dynamic strength of concrete increased linearly with the viscosity of pore liquid,and validated the beneficial effect of water viscosity on the dynamic properties of concrete that is called as Stefan effect.The dynamic strength of concrete with incorporated water can be decomposed into dry static strength,weakened part of water,inertial term and viscosity effect.The increase of dynamic strength of wet concrete is mainly attributed to inertial action and water viscosity.?4?According to the theory of fracture mechanics,the internal load caused by Stefan effect reduces the effective splitting tensile stress on the concrete crack surface,and thus prolongs the time of the concrete crack strength factor reaching the fracture toughness.As a result,the appearance compressive strength and the DIF both increased.