Study On Oxygen Diffusion Coefficient Of Cementitious Material And Its Effect On Reinforced Corrosion

As one of the necessary conditions for steel corrosion,oxygen and water have an important influence on the corrosion rate of reinforcement in concrete structures.At present,there are few studies on oxygen diffusion in cementitious materials and the measurement devices or testing methods of oxygen diffusion coefficient are insufficient.Therefore,a prediction model of oxygen diffusion coefficient in cementitious materials under different porosity saturation and drying conditions is established in this paper.What's more,a set of experimental device for determining oxygen diffusion coefficient in cementitious materials is designed independently.The oxygen diffusion coefficient in mortar and concrete are measured by this device then.Futherly,the theoretical value of the model is compared with the experimental results and analyzed.In addition,to explain the effect of oxygen concentration and ambient humidity on the corrosion rate of reinforcement in concrete,the corrosion current density and corrosion amount of the steel under different oxygen concentration and ambient humidity were tested.The main contents of this paper are as follows:(1)Based on the three diffusion modes of oxygen in cement-based materials(Fick diffusion,Knudsen diffusion and Transition diffusion),and then pore structure of cement-based materials is simplified as a parallel tube bundle model.The three diffusion modes are quantified by the aperture density function.Combined with the porosity and tortuosity,the prediction model of oxygen diffusion coefficient in cementitious materials under dry condition and different pore saturation is established.What's more,the related parameters are analyzed.(2)In view of the shortage of oxygen diffusion coefficient testing device and measurement method in the cementitious materials,based on the Fick diffusion law,a measuring device for oxygen diffusion coefficient in cementitious materials is designed independently,and the oxygen diffusion coefficient under the drying conditions and different pore saturation of the mortar specimens is tested.The experimental results are analyzed and then compared with the theoretical value to verify the model.Meanwhile,the internal oxygen concentration in the diffusion process of mortar specimens was monitored in real time,and the oxygen diffusion rule in mortar specimens was further explored.(3)Consider the structural difference between concrete and mortar,to furtherly verify the accuracy of the diffusion coefficient model in concrete,the oxygen diffusion coefficient in concrete under different pore saturation was tested by using the measuring device of oxygen diffusion coefficient,and the results were compared with the theoretical values.The correctness and completeness of the prediction model of oxygen diffusion coefficient in cementitious materials is reasonably expounded.At the same time,the change of oxygen concentration in the diffusion process of the concrete specimen is monitored in real time,and the oxygen diffusion rule in the concrete specimen was further explored.(4)Using the prediction model of oxygen diffusion coefficient in the cementitious materials,the existing corrosion rate models are selected and calculated,and then the results are compared and analyzed.On the other hand,by artificial oxygen environment box,the corrosion rate and corrosion amount of steel in concrete under different oxygen concentration and ambient humidity were tested.Then the influence of oxygen concentration and ambient humidity on corrosion was analyzed,then the test results of corrosion rate were compared and verified with the theoretical value of existing steel corrosion rate model.