| Concrete will suffer serious calcium leaching when it is in a water-immersed environment,and the deterioration of its mechanical properties will lead to the degradation of structural performance of a concrete structure.To study the degradation law of concrete structures during service,it is of great significance to establish a reasonable deterioration model to predict the mechanical properties of leached concrete,and the temporal and spatial distributions of seepage leaching of mass concrete structures are more suitable to be simulated by numerical methods.Firstly,the accelerated leaching experiments were carried out for three kinds of cement-based materials,and the compressive strength,layer splitting tensile strength,leaching depth,and leaching amount of calcium ion were tested.Using the cumulative relative leached calcium ion as the aging index,deterioration prediction models were established for the compressive strength and layer splitting tensile strength.The XRD diffraction analysis was carried out for the cement paste specimen immersed in nitric acid solution with different concentrations,and the accelerated leaching mechanism and acceleration law of the nitric acid solution were explored.Secondly,based on the Gérard calcium leaching theory,the contact leaching model and seepage leaching model were established on the COMSOL platform.The relationships between the concentration of the nitric acid solution and the accelerated leaching effect were inverted,and the temporal and spatial distributions of seepage leaching of concrete dams were studied.The differences of deterioration degree of concrete dams with respect to the balanced and imbalanced relationships between concentrations of the solid and liquid calcium were then compared,and the strength deterioration of concrete inside the dam body was evaluated according to the compressive strength prediction model.Research results are concluded as follows:(1)the compressive strength and layer splitting tensile strength of leached concrete decrease with the cumulative relative leached calcium ion,which shows an exponential function and a linear function relationship,and the two strengths are reduced to 60%when the former reaches 9.7% and 23.12%,respectively.(2)The leaching process of cement-based materials immersed in the nitric acid solution also satisfies the Fick’s diffusion law.Within the concentration range of 0.01-0.5mol/L,the accelerated calcium leaching effect of the nitric acid solution on cement-based materials is linearly proportional to the concentration.For cement paste,mortar and concrete specimens with a water-cement ratio of 0.5,the equivalent accelerated diffusion coefficients and accelerated ratio are23.45,15.98,11.09 times and 3793.67,1602.72 and 1017.45 times of the concentration of the nitric acid solution,respectively.(3)The seepage leaching of a concrete dam emerges from the surface to inside of the dam body,and the main leaching area is the upstream side of the dam body.If the solid-liquid balance equation,which is obtained by the contact leaching experiments,is used for the seepage leaching of concrete dams,the seepage leaching zone of dam body is relatively small,but the leaching degree of leached regions will be obviously larger than that of the actual situation.Under the balanced mode of the solid-liquid concentration,all regions of the dam body are leached.In order to consider the influence of the uncertainty of this calculation mode,it is recommended that the leaching degree of each part of the dam body should be taken as the larger value between the balanced and imbalanced modes.After 100 years of seepage leaching,the degrees of calcium leaching of an 85 m high concrete gravity dam are 1.13% and 0.03%at the depths of 3 and 30 m from the upstream face of the dam body,which leads the compressive strength reduce to 94.29% and 99.86%,respectively. |
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