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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 88
PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping and M. Papadrakakis
Paper 263

Modelling the Effect of Chloride Binding on Chloride Diffusion in Concrete Structures

A.H. Al-Gadhib1, I.A. Mahmoud1, M.A. Shazali2 and M.H. Baluch1

1Department of Engineering, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia
2Precast Engineering Division, Industrial Contractors, Al-Khobar, Saudi Arabia

Full Bibliographic Reference for this paper
A.H. Al-Gadhib, I.A. Mahmoud, M.A. Shazali, M.H. Baluch, "Modelling the Effect of Chloride Binding on Chloride Diffusion in Concrete Structures", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 263, 2008. doi:10.4203/ccp.88.263
Keywords: modelling, diffusion, concrete durability, corrosion, chlorides, thermal analogy, ANSYS.

Summary
Reinforced concrete has been very common and widely used as a construction material for civil infrastructure and building structures. However, its durability and sustainability has remained of great concern to structural engineers and clients from point of view of its service life and safety under the influence of external environmental conditions.

The main thrust of this paper is to establish a numerical model based on a nonlinear finite element method to predict the diffusion of chloride into concrete structures. The formulation of the numerical model is implemented considering the chemo-physical phenomena associated with various bounded chloride functions and its influence on chloride diffusivity. It has been shown that the total chloride diffusivity is nearly three times the free chloride diffusivity [1]. That is to say, the bound chloride content is about two times the free one. Results from the analysis including the effect of bounded-chloride formulation on the diffusion behaviour of chloride have been assessed and highlighted.

This paper focuses on the influence of binding chloride and its impact on the way the chloride front moves within concrete cover through the key parameter, the chloride diffusivity. An in-house software CCICS, (chloride computation in concrete structures) based on a nonlinear finite element method was developed, which predicted well the movement of chloride front through concrete. The CCICS is mainly an extension of a program used to predict moisture diffusion in cementitious materials [2]. The role of the specific form of the binding chloride has been demonstrated, which produces a marked difference in predicting the free chloride and its associated binding chloride and ultimately the total chloride. The results predicted by the software have been cross-checked by an independent source of software, namely ANSYS, where close agreement has been ascertained. It is clear that a low value of the chloride diffusivity parameter plays an important role on improving concrete durability and thus prolonging the service life of concrete structures. Feasibility of the results of this investigation to match with that of experimental findings has been established.

References
1
A. Neville, "Chloride attack of reinforced-concrete - an overview", Materials and Structures, 28, 63-70, 1995. doi:10.1007/BF02473172
2
M.K. Rahman, M.H. Baluch, A.H. Al-Gadhib, "Modeling of shrinkage and creep stresses in concrete repair", ACI Materials Journal, 96(5), 542-550, 1999.

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