Prediction of chloride ingress into saturated concrete on the basis of a multi-species model by numerical calculations

A multi-species model based on the Nernst-Planck equation has been developed by using a finite volume method. The model makes it possible to simulate transport due to an electrical field or by diffusion and to predict chloride penetration through water saturated concrete. The model is used in this paper to assess and analyse chloride diffusion coefficients and chloride binding isotherms. The experimental assessment of the effective chloride diffusion coefficient consists in measuring the chloride penetration depth by using a colorimetric method. The effective diffusion coefficient determined numerically allows to correctly reproduce the chloride penetration depth measured experimentally. Then, a new approach for the determination of chloride binding, based on non-steady state diffusion tests, is proposed. The binding isotherm is identified by a numerical inverse method from a single experimental total chloride concentration profile obtained at a given exposure time and from Freundlich`s formula. In order to determine the initial pore solution composition (required as initial conditions for the model), the method of Taylor that describes the release of alkalis from cement and alkali sorption by the hydration products is used here. Finally, with these input data, prediction of total and water-soluble chloride concentration profiles has been performed. The method is validated by comparing the results of numerical simulations to experimental results obtained on various types of concretes and under different exposure conditions.

[1]  Baroghel-Bouny,et al.  Transferts dans les betons et durabilite des ouvrages. Determination experimentale des gradients resultant d'une interaction hydratation-sechage dans une dalle de beton , 2002 .

[2]  James J. Beaudoin,et al.  Modeling chemical activity effects in strong ionic solutions , 1999 .

[3]  A. K. Nickerson,et al.  The diffusion of ions through water-saturated cement , 1984 .

[4]  Luping Tang,et al.  ELECTRICALLY ACCELERATED METHODS FOR DETERMINING CHLORIDE DIFFUSIVITY IN CONCRETE - CURRENT DEVELOPMENT , 1996 .

[5]  M. Carcasses,et al.  A new way for determining the chloride diffusion coefficient in concrete from steady state migration test , 2000 .

[6]  Lars-Olof Nilsson,et al.  Chloride binding capacity and binding isotherms of OPC pastes and mortars , 1993 .

[7]  Della M. Roy,et al.  Diffusion of ions through hardened cement pastes , 1981 .

[8]  Stuart Lyon,et al.  Mechanism of Friedel's salt formation in cements rich in tri-calcium aluminate , 1996 .

[9]  J. Marchand,et al.  Calculation of ionic diffusion coefficients on the basis of migration test results , 2003 .

[10]  V. Papadakis.  Effect of supplementary cementing materials on concrete resistance against carbonation and chloride ingress , 2000 .

[11]  H. Taylor.  A method for predicting alkazi ion concentrations in cement pore solutions , 1987 .

[12]  Marta Castellote,et al.  Non-steady-state chloride diffusion coefficients obtained from migration and natural diffusion tests. Part I: Comparison between several methods of calculation , 2000 .

[13]  F. Glasser,et al.  Alkali binding in cement pastes: Part I. The C-S-H phase , 1999 .

[14]  J. Larbi,et al.  The chemistry of the pore fluid of silica fume-blended cement systems , 1990 .

[15]  H. Brouwers,et al.  Alkali concentrations of pore solution in hydrating OPC , 2003 .

[16]  John A. Nelder,et al.  A Simplex Method for Function Minimization , 1965, Comput. J..

[17]  C. Page,et al.  Modelling of electrochemical chloride extraction from concrete : Influence of ionic activity coefficients , 1998 .

[18]  E. Samson,et al.  Predicting the performance of concrete structures exposed to chemically aggressive environment—Field validation , 2002 .

[19]  Marta Castellote,et al.  Chloride-binding isotherms in concrete submitted to non-steady-state migration experiments , 1999 .

[20]  Ahmed Loukili,et al.  Predicting Ca(OH)2 content and chemical shrinkage of hydrating cement pastes using analytical approach , 2004 .

[21]  Samson,et al.  Numerical Solution of the Extended Nernst-Planck Model. , 1999, Journal of colloid and interface science.

[22]  F. P. Glasser,et al.  Friedel’s salt, Ca2Al(OH)6(Cl,OH)·2H2O: its solid solutions and their role in chloride binding , 1998 .

[23]  V. Baroghel-Bouny,et al.  Which toolkit for durability evaluation as regards chloride ingress into concrete? Part II: Development of a performance approach based on durability indicators and monitoring parameters , 2005 .

[24]  Olivier Francy,et al.  Modelisation de la penetration des ions chlorures dans les mortiers partiellement satures en eau , 1998 .

[25]  Luca Bertolini,et al.  Simulation of chloride penetration in cement-based materials , 1997 .

[26]  James J. Beaudoin,et al.  Interaction of chloride and CSH , 1990 .