Computational Modelling of Chloride Ion Transport in Reinforced Concrete

Abstract

* Delft university of technology, faculty of civil engineering and geosciences, materials science group ** Delft university of technology, Koiter institute / faculty of aerospace engineering Exposure to a saline environment is a major threat with respect to the durability of reinforced concrete structures. The chloride ions, which are present in seawater and de-icing salts, are able to penetrate the concrete up to the depth of the reinforcement. They can eventually trigger a pitting corrosion process. The assessment of a corrosion-free service life of concrete structures is of paramount economic interest. However, the modelling of the ingress of chloride ions is complicated due to various influencing factors and transport mechanisms. Here a computational model for chloride ion transport through a porous material is presented. Chloride ion transport in rein- Key words: chloride penetration, reinforced concrete, corrosion, coupled transport, porous media IntroductionThe design of concrete structures involves mainly the evaluation of strength, stability and durability. A major threat to concrete durability is chloride. As chlorides are present in salty water and deicing salts, special care has to be taken in the design of off-shore structures, bridges and parking garages. Also buildings in coastal areas are subjected to chloride ion ingress. The deterioration mechanism is the following: chloride ions penetrate the concrete to the level of the reinforcement, when they are in a sufficient quantity they depassivate the rebars, pitting corrosion starts if also oxygen is available, the effective cross section of the rebars decreases and cracks appear due to the expansion of rust products. The cracks and the decrease of the effective cross section of the reinforcing steel bars imply a strength loss, while the cracks also enhance the deterioration process.Chloride ion ingress in reinforced concrete has been subject of research for many decades and tra- HERON, Vol. 46, No.3 (2001) ISSN 0046-7316 207 ditionally this process has been modelled by Fick's second law. The only material parameter in this model is the effective chloride diffusion coefficient. The adjective "effective" already suggests that many effects are hidden in this coefficient. Very few attempts have been made to substantially refine the modelling, e.g. by [Saetta 1993]. With the aid of current computing techniques, complex problems can be solved which could not be handled in the time the effective diffusion approach was proposed. Here a refined approach is presented based on the interaction of three simultaneous processes: chloride ion transport, moisture migration and heat flow. The model also takes into account the inhomogeneous character of concrete on the meso-level. Three components are distinguished:mortar, aggregates and interfacial transition zones. Model structure 208The distance from the concrete surface to the reinforcement bars amounts to a few centimeters approximately. This is the distance which the chloride ions have to travel before they ...

A three-phase model for predicting the effective chloride migration coefficient of ITZ in cement-based materials

“…Yang and Su (2002) used an accelerated chloride migration test (ACMT) and regression analysis results to investigate the effect of aggregate content on the chloride migration coefficient of mortar, and determined the approximate chloride migration coefficient of ITZ. Meijers et al (2001) stated that different influencing factors and transport mechanisms complicated the ingress of chloride ions. Hence, chloride ion transport in concrete is modelled by three coupled equations for heat, moisture and chloride ion transport.…”

A multi-phase model for predicting the effective chloride migration coefficient of ITZ in cement-based materials

“…For diffusivity ability of concrete, it is regarded as significant index that observes the service life of reinforced concrete structures (Martin-Perez et al 2003). Meijers et al (2001) described that complicating of the ingress of chloride ions is caused by the different influencing factors and transport mechanisms, such as heat, moisture and chloride Corresponding author, Professor, E-mail: ccyang@mail.ntou.edu.tw 1a Ph.D., E-mail: hannahgirl1102@gmail.com ions transport. Meijers et al (2001) also developed a finite element modelby three coupled equations.…”

“…Meijers et al (2001) described that complicating of the ingress of chloride ions is caused by the different influencing factors and transport mechanisms, such as heat, moisture and chloride Corresponding author, Professor, E-mail: ccyang@mail.ntou.edu.tw 1a Ph.D., E-mail: hannahgirl1102@gmail.com ions transport. Meijers et al (2001) also developed a finite element modelby three coupled equations. To investigate chloride diffusion into concrete, the effect of w/c ratio, hydration degree, volume fraction of aggregate, distributing of aggregate particle size, thickness of interfacial transition zone, and air content have to be considered.…”