Chloride ion transmission model under the drying-wetting cycles and its solution

Abstract

The chloride ion transmission model considering diffusion and convection was established respectively for different zones in concrete by analyzing chloride ion transmission mechanism under the drying-wetting cycles. The finite difference method was adopted to solve the model. The equation of chloride ion transmission model in the convection and diffusion zone of concrete was discreted by the group explicit scheme with right single point (GER method) and the equation in diffusion zone was discreted by FTCS difference scheme. According to relative humidity characteristics in concrete under drying-wetting cycles, the seepage velocity equation was formulated based on Kelvin Equation and Darcy’s Law. The time-variant equations of chloride ion concentration of concrete surface and the boundary surface of the convection and diffusion zone were established. Based on the software MATLAB the numerical calculation was carried out by using the model and basic material parameters from the experiments. The calculation of chloride ion concentration distribution in concrete is in good agreement with the drying-wetting cycles experiments. It can be shown that the chloride ion transmission model and the seepage velocity equation are reasonable and practical. Studies have shown that the chloride ion transmission in concrete considering convection and diffusion under the drying-wetting cycles is the better correlation with the actual situation than that only considering the diffusion.

Keywords

under the drying-wetting cycles / the chloride ion transmission model / the group explicit scheme / seepage velocity

References

[1] Maekawa K, Chaube R, Kishi T Modeling of Concrete Performance: Hydration, Microstructure and Mass Transport[M], 1999 London E&FN Spon

[2] Thomas M D A, Matthews J D Performance of pfa Concrete in a Marine Environment-10-year Results[J]. Cement and Concrete Composites, 2004, 26: 5-20.

[3] Saetta A V, Scotta R V, Vitaliani R V Analysis of Chloride Diffusion into Partially Saturated Concrete[J]. ACI Materials Journal, 1993, 90(5): 441-451.

[4] Yu H, Sun W, Ma Haiyan Diffusion Model of Chloride in Concrete I-Homogeneous and Inhomogeneous Diffusion in Infinite Body[J]. Journal of Naijing University of Aeronautics & Astronautics, 2009, 41(2): 226-280.

[5] Yu H, Sun W, Ma Haiyan Diffusion Model of Chloride in Concrete II-Homogeneous and Inhomogeneous Diffusion in Infinite Body[J]. Journal of Naijing University of Aeronautics & Astronautics, 2009, 41(3): 408-413.

[6] Zhang Yi Mechanics of Chloride Ions Transportion in Concrete[D], 2008 Hangzhou Zhejiang University

[7] Jin Libin Multi-Environmental Time Similarity(METS) Theory and Its Application in Coastal Concrete Structural Durability[D], 2008 Hangzhou Zhejiang University

[8] Kong X Advanced Mechanics of Fluids in Porous Media[M], 1999 Beijing Press of University of Science and Technology of China

[9] Bazant Z P, Najjar L J Nonlinear Water Diffusion in Nonsaturated Concrete[J]. Materials and Structure, 1972, 5(25): 3-20.

[10] L E Copeland, R H Bragg. Self-desiccation in Portland Cement Pastes[R]. Portland Cement Association for Testing Materials, No.52

[11] Akita H, Fujiwara T, Ozaka Y A Practical Procedure for the Analysis of Moisture Transfer within Concrete due to Drying[J]. Magazine of Concrete Research, 1997, 49(179): 129-137.

[12] Thomas M D A, Bentz E C Life-365: Service Life Prediction Model and Computer Program for Predicting the Service Life and Lifecycle Costs of Reinforced Concrete Exposed to Chlorides[M], 2001 St Paul Cortec Corporation

[13] Mangat P S, Limbachiya M C Effect of Initial Curing on Chloride Diffusion in Concrete Repair Materials[J]. Cement and Concrete Research, 1999, 29(9): 1 475-1 485.

[14] Steinar H Assessment and Prediction of Service Life for Marine Structures: a Tool for Performance based Requirement[M], 1999 Berlin World Publishing Corporation

[15] Mangat P S, Gurusamy K Chloride Diffusion in Steel Fibre Reinforced Concrete Containing Pfa[J]. Cement and Concrete Research, 1978, 17(4): 640-650.

[16] Wei J, Gui Z, Wang Yilin Modeling on Predicting Steel Corrosion Rate in Concrete[J]. Journal of Wuhan University of Technology, 2005, 27(6): 45-47.

[17] Zhao Y, Wang Z, Jin W, . Experimental Analysis on Time-dependent Law of Surface Chloride Ion Concentration of Concrete[J]. Journal of Civil, Architectural and Environmental Engineering, 2010, 32(3): 8-13.

[18] Hong K, Hooton R D Effects of Cyclic Chloride Exposure on Penetration of Concrete Cover[J]. Cement and Concrete Research, 1999, 29(9): 1 379-1 386.

[19] Xinlong F, Huan Wang GER Method for a Kind of Convection Diffusion Equation with Variable Coefficients[J]. Chinese Journal of Engineering Mathematics, 2004, 21(6): 1 021-1 024.

[20] Wei J, Wang T, Dong R, . Influencing Research of Chloride on Reinforced Concrete Material under Dry-wet Cycle[J]. Concrete, 2010, 224: 4-6.