Test And Boundary Element Analysis For Chloride Diffusion In Concrete

Chloride diffusion in concrete is a nonlinear dynamic behavior and a complicated physiochemical process; Fick's second law is used to discuss this process by valid simplification. This paper establishes the boundary element method (BEM) for one-dimensional and two-dimensional diffusion analysis of chloride ion in two-dimensional concrete structures along with the concept of computing length and its expression for the first time base on Fick's second law. No discretizing mesh is required for the time domain for one-dimensional diffusion problem. Few discretizing meshes are required for the time domain for two-dimensional diffusion problem, so that fewer unknowns are resulted in and little computing time is required, while the spatial domain is discretized along the boundary of the computing diffusion field in the BEM model, which reduces the computation time steeply, compared with the other methods. Several examples in the paper demonstrate the efficiency and accuracy of the presented method, in which the results by the BEM is compared with those by the FEM and the analytical one. Furthermore, the distribution of chloride concentration near the intersection of the exposed surface and the diagonal is increasing evidently, which shows that the two-dimensional analysis of chloride diffusion can reflect the real aspects of chloride diffusion and concentration in the concrete structures, compared with the one-dimensional analysis methods.In this paper, High Performance Concrete (HPC) with low water binder and large amounts of fly ash that has better workability, mechanical property and durability than normal concrete (NC) are prepared successfully. The prepared conditions are selected as follow that water to binder ratio is 0.33 , and slump of fresh concrete was over 180mm. Fly ash was used to partially replace cement at 0%, 30%, 50%, 70% by weight of cementitious material. Chloride resistance of concretes is evaluated using the measurement of the coulomb charge as per ASTM C1202. The rapid chloride permeability test (ASTM C1202) clearly indicates that the coulomb charge of concrete at the age of 28 days is significantly reduced with the incorporation of fly ash, the resistance to chloride penetration of concrete is significantly reduced with the incorporation of fly ash. Fly ash concrete with 50% replacements, provided the best result of corrosion resistance. From the tests, it is found that near the surface the concentration of the chloride binding of concrete is reduced with the diffusion depth, it will reach a plateau when the depth beyond certain range.In the paper, the results by the experiment is compared with those by the BEM and the analytical one, the results by the BEM and the analytical fits the experimental data well at certain points in time. So the time relationship between the RCPT and practical chloride diffusion of concrete is established. It is found on analysis that the practical chloride diffusion time which corresponding to the time of RCPT of the normal concrete is shorter than the concrete which fly ash is used to partially replace cement, so the fly ash concretes provided the better result of corrosion resistance than the normal concrete.