Study And Improvement On The Ring Restrained Shrinkage Test

How to improve crack resistance of concrete is the most urgent technical difficulties of concrete engineering technology. If you want to improve crack resistance of concrete, you have to research influencing factor of crack resistance of concrete. So a good test method is the prerequisite of improve crack resistance of concrete. For numerous method of study crack resistance of concrete, the ring restrained shrinkage method is widely used. But it have a issue of diverging of crack location, so this article propose a revised the ring restrained shrinkage method. For deepen understanding of the ring restrained shrinkage method and demonstrate the feasibility of revised the ring restrained shrinkage method, this article do the following studies and get the following conclusion:(1)Based on the comprehensive reading of references about dry shrinkage of concrete, the humidity diffusion of concrete, this article get relative humidity governing equation, physical equation of stress-filed, geometric equation of stress-filed, equilibrium equation of stress-filed. At the same time, this article also get moisture diffusion coefficient, water exchange coefficient and so on.(2)According to the actual conditions of the ring restrained shrinkage method, this article select element type of ANSYS. According to Galerkin and virtual work principle, this article gets finite element of relative humidity-field and finite element of stress-field. At the same time, this article set up numerical model of finite element analysis.(3)Through numerical simulation and analysis by ANSYS, this article study distributions of 1st Principal stress and relative humidity of concrete module in the ring restrained shrinkage method. The study result shows that minimum value of 1st Principal stress of concrete module and minimum value of relative humidity of concrete module appear on the outside edges of concrete module. With the decrease of radial distance, relative humidity gradually increasing, 1st Principal stress gradually decreasing. On the inward flange of concrete module, 1st Principal stress reaches the minimum, relative humidity reaches the maximum. This result shows that there is a problem of the ring restrained shrinkage method.(4) Through numerical simulation and analysis by ANSYS,this article study that the strength grades of concrete, elastic modulus of steel ring, size of steel ring make a difference to the distributions of 1st Principal stress and relative humidity of concrete module. The study result shows that the diffusion process of concrete gradually diminishes and 1st Principal stress gradually decreasing with the increase of concrete strength grade. With the increase of elasticity modulus of steel ring and size of steel ring, 1st Principal stress also gradually increasing.So, when tester make use of the ring restrained shrinkage method to test the concrete crack resistance, the increase of elasticity modulus of steel ring and size of steel ring is good.(5) Through numerical simulation and analysis by ANSYS, this article study distributions of 1st Principal stress and relative humidity of concrete module in the revised ring restrained shrinkage method. The study result shows that maximum value of 1st Principal stress of the same cross section and minimum value of relative humidity of the same cross section appear on the outside edges of concrete module. Along the outer edge of concrete specimens, from the minimum cross section to the maximum cross section, 1st Principal stress and relative humidity on points that exists an equivalent to the outside edge of concrete module, relative humidity gradually increasing, 1st Principal stress gradually decreasing. The minimum value of relative humidity and the maximum of 1st Principal stress appear the outside edges of the same cross section on the whole specimen. With the increase of eccentricity, this rule will become more apparent. So when you make use of the revised ring restrained shrinkage test to study the crack resistance of concrete, the place crazed of concrete module certainly appear the minimum cross section. These results indicate that using the revised ring restrained shrinkage test guiding the place crazed of concrete module is feasible. With the increase of eccentricity, this guiding function will become more apparent.(6) Through numerical simulation and analysis by ANSYS,this article study that the strength grades of concrete, elastic modulus of steel ring, size of steel ring make a difference to the distributions of 1st Principal stress of the minimum cross section of concrete module. When the eccentricity is same, the results prove that the diffusion process of concrete gradually diminishes and 1st Principal stress gradually decreasing with the increase of concrete strength grade. With the increase of elasticity modulus of steel ring and size of steel ring, 1st Principal stress of the minimum cross section also gradually increasing. So, when tester make use of the revised ring restrained shrinkage test to test the concrete crack resistance, the increase of elasticity modulus of steel ring and size of steel ring is good.