Research On Carbonization Of Concrete Box Girder Under Bending Load

Concrete structure is one of the most widely used structures forms at present.The research of its durability has been paid much attention by researchers both in our country and abroad.Carbonation is an important factor affecting the durability of concrete.Study on carbonation process,understand the cause and development law of carbonization process is beneficial to us to solve the carbonation problem of concrete in essence.And thus improving the durability and safety of structures.In this paper,the carbonation law of concrete box girder is studied through the accelerated carbonation experiment of concrete box girder.The bending tension loading device is customized to study the carbonization law of box girder with Bending load.The box girder is numerically simulated by finite element software.And the validity of the numerical method is verified.The main contents of this paper are as follows:(1)Based on the chemical reaction process of carbonization and the theory of diffusion law,the differential equation of carbonation reflecting concrete is derived,and the prediction models of carbonation depth are introduced and compared in terms of application range and applicable conditions.The carbonation law of concrete structures under natural environment is studied by using the analysis method of fuzzy theory,and the calculation model is obtained.(2)The rapid carbonization test was carried out under the condition of carbonation time and CO2 concentration.The reaction rate of the outer angle of the box girder model is the highest.About twice as much as the inner angle.When the concentration of CO2 increased to 2 times,the maximum carbonation depth increased to 1.22 times with the change of reaction time.And when the carbonization reaction time increased to 2 times,the carbonation depth increased to 1.34 times with the change of the concentration.The results show that carbonation reaction time has more influence on carbonation depth than the concentration of CO2 in the accelerated carbonation experiment of box girder without consideration of load.(3)By customizing the loading device and determining the loading grade,the accelerated carbonation experiment of box girder under flexural load was carried out to study the influence of stress level on the carbonation depth of concrete.When the load on the box girder is larger,the inhibition effect of compressive stress on carbonation is more obvious,that is,the greater the compressive stress,the smaller the carbonation rate.The inhibition effect of compressive stress on carbonation is more obvious.The effect of tensile stress on carbonization increases with the increase of tensile stress,that is,the greater the tensile stress,the faster the carbonation rate increases.Based on the analysis of carbonation depth data of box girder under load,the concrete carbonation depth calculation model under stress is obtained by numerical fitting.(4)The similarity between the solution of ANSYS heat conduction and the carbonation process of concrete is demonstrated,and the numerical simulation is used to solve the carbonation problem of concrete.The results of numerical simulation show that the tensile and compressive stress can promote and inhibit carbonization,and the trend of the influence curve is basically the same as that of the test results.In the case of compressive stress,the numerical simulation results are slightly larger than the experimental values under each working condition,and the maximum deviation between the two by calculation is 12%.In the case of tensile stress,the numerical simulation results are close to the experimental results.The carbonization depth of a box-girder bridge in practical engineering is calculated numerically and its carbonization depth is predicted.