Chloride Transportation In The Cracked Concretes

Chloride ingression is a main cause for the durability of reinforced concrete structures subjected to marine and de-icing salt environments.Furthermore,the inevitable cracks in real structures have a significant effect on the transportation of chloride ions.Therefore,it is very important to figure out the mechanism of chloride ingress in cracked cement-based materials.Because of the randomness and the complexity of concrete cracks,the available studies on chloride transportation in cracked cementitious materials are still controversial.To clarify the effects of cracks on chloride transportation,the following contents are studied by using chloride ponding test,electron probe microanalysis(EPMA)and numerical inversion methods.1.Cement-based specimens with different mix proportions were cracked using splitting method,by which the cracks with different widths were induced.Then,the EPMA was adopted to measure the distribution of chloride ions on the cross section of cracked specimens after chloride ponding test.To validate the effectiveness,the results of EPMA was compared with the results from traditional methods.2.Considering the porosity and the chloride binding effect of cement-based material,theoretical model of chloride diffusion in cracked specimen was established on the basis of the existing models.The simulation results of different theoretical models were compared,and the effect of different crack's parameters on the ions diffusion was analyzed.3.Based on the digital image technology,the meso-structure models of cracked concretes were established.The MATLAB software was used to process the EPMA scanning results and to obtain the calculation parameters by data fitting.Through the numerical inversion analysis using COMSOL software,the influences of crack width,self-healing effect,crack roughness and connectivity on the chloride diffusion was revealed.The results show that the spatial resolution of EPMA is much higher than that of the traditional method.EPMA can effectively detect the chloride distribution on the cross section of the specimen.However,the preparation process of EPMA method is very complex,and this method can't distinguish the free and the bound chloride ions.It is necessary to cooperate this method with other traditional methods.The existing chloride diffusion models for cracked specimens are not satisfied with the assumption of homogeneous materials.As a result,the simulation results may underestimate the chloride ingression.Numerical inversion results show that the chloride diffusion coefficient of cracked concrete was independent of either crack width or mix proportion,the chloride diffusion coefficient in the crack were similar to that in the water.