Chloride-induced-corrosion of steel bars embedded in concrete: A review Dr. Anwar Khitab Department of Civil Engineering MIRPUR UNIVERSITY OF SCIENCE AND TECHNOLOGY MIRPUR, AZAD KASHMIR

How chloride ions penetrate through concrete Cl- Saline Water Concrete Reinforcement X (distance from concrete surface) Chloride concentration Chloride Profile Time

Impact on Structures

Chloride profiles in reinforced concrete

Prediction of corrosion with chloride penetration into concrete

Modelling of chloride diffusion through cementitious materials The typical approach to characterize diffusive transport of ions in porous materials begins with Fick’s law of diffusion. Whenever a concentration gradient of a species c/x exists in a substance, the species will have the natural tendency to move in order to distribute itself more evenly within the substance and decrease the gradient. The mathematics of this transport mechanism was formalized in 1855 by Adolf Fick, who, while working with salts postulated that the flux of material across a given plane is proportional to the concentration gradient across that plane.

Drawbacks of Fick’s Law Penetration of chlorides: One of the major causes of corrosion of steel bars in concrete Classical Approach: Fick’s Laws (For molecules) Correct Approach: Equation of Nernst-Planck (For ions) Fick’s 2nd law Nernst-Planck Di

Mathematical Solution of Fick’s second Law                                                                    (x14)                                                                   gaussian.xls - gausslin.gif Mathematical Solution of Fick’s second Law x = Distance from the surface Cs = Environmental surface concentration of chlorides Erfc = Error function D = Chloride diffusion coefficient in concrete, a measure of chloride speed in concrete t = Duration of exposure to chloride

Nernst Planck Equation Different Models Fick’s Law Nernst Planck Equation Error Function Law False Error Function Law Duracrete ClinConc SELMER Hetek JSCE Life-365 LEO LERM Li and Page STADIUM Johannesson STANISH MsDiff

What common input parameters are needed to run the model Chloride diffusion coefficient Initial chloride concentration within concrete Environment chloride concentration

How chloride diffusion coefficient is determined? By immersion tests (Minimum 35 days) By Diffusion cell methods (extends over years) By electrochemical methods (Maximum one week)

Immersion Tests NaCl solution Concrete specimen Cl-

Diffusion and Electrochemical Tests Solution containing chlorides Same Solution without chlorides Concrete specimen Solution containing chlorides Same Solution without chlorides Concrete specimen

Modelling and Simulations with Erfc model

Modelling with MsDiff

Conclusions The chloride ingress models, based on Fick’s laws of diffusion are quite simple but unfortunately not correct. The models based on Nernst Planck equation are although sofiticated and correct but a lot of input parameters. In Fick’s laws models, total chloride profiles are only calculated, which again is not a correct approach because in reality, these are free chlorides present only in the pore solution, which are resposible for the initiation of corrosion.

Publications on the topic by the Author Ionic transport through saturated and reactive porous media, NATO Advanced Study Institute: Emerging Technologies in Porous Media, June 9-20, 2003. Chloride diffusion through saturated concrete: numerical and experimental results, Advances in Concrete through Science and Engineering, Evanston (Illinois, USA), March 21-26, 2004. Ionic contamination and decontamination of porous media, NATO Science Series for Peace: Physics, Chemistry, Mathematics, pp. 409-417, Springer, Netherlands, 2004. Predictive model for chloride penetration through concrete, Magazine of Concrete Research Vol:57 pp:511-520, 2005. Chloride attack through concrete: time effects, (2006) ACI Special Publications Vol:234 pp:191-2006. Modeling of Chloride Penetration through concrete, First Abasyn International Conference on Management and Technology (ABICMT-2013), May 2013, Peshawar. Modeling of Chloride Diffusion through Concrete using Fick’s laws of Diffusion, 2nd Annual Computational Science Conference, October 20-25, 2013, International Islamic University, Islamabad. Modeling Of Chloride Ingress In Concrete Using Fick's Laws: Review And Historical Perspective, Sci.Int. 26(4),1519-1521, 2014 ISSN 1013-5316.