Impedance spectroscopy: An efficient tool to determine the non‐steady‐state chloride diffusion coefficient in building materials

Abstract

One of the most important problems of reinforced steel concrete in marine environments is the corrosion of the reinforcing bars. Most of the times, this corrosion is a consequence of the local destruction of the passive layer formed on the surface of the embedded steel, due to the arrival of chlorides present in the environment. Many efforts have been made to determine the chloride diffusion coefficient in concrete structures, both using natural diffusion methods, and accelerated migration methods. This coefficient determines the velocity of ingress of chlorides, and as a consequence the life time of the structures. In this work it is presented the possibility of using the technique of impedance spectroscopy, that is, very simple to use and requires no chemical or conductivity measurement, to determine the value of the non-steady-state diffusion coefficient. This technique, together with the equivalent circuits proposed for the interpretation of the measurements, allows the determination of the chloride saturation of a concrete or mortar sample. Pores of the material that are initially filled with water have high resistivity, and as the chlorides penetrate into the sample the value of the resistivity decreases. This diminution can be determined in situ, and permits the calculation of the diffusion coefficient saving experimental time and efforts. The results have been obtained both with concrete and mortar samples, and using different cement types.

Influencia de diferentes condiciones de curado en la estructura porosa y en las propiedades a edades tempranas de morteros que contienen ceniza volante y escoria de alto horno

“…Many studies (4,5) have demonstrated that, for optimum laboratory conditions, the use of active additions produces a substantial improvement in chloride ingress resistance. In the particular case of CEM III, their better behaviour against chloride ingress could be related to the possible formation of Friedel's salt, because this cement has a higher content of Al 2 O 3 from the slag.…”

“…Many studies (1,3,4) have shown that, exposed to optimum laboratory conditions, the cements which incorporate these additions present a good behaviour with regard to service properties, even better than that observed for Portland cement (5,6). Blast-furnace slag has hydraulic properties, therefore it would start to react since the setting moment, while fly ash has pozzolanic properties, so their particles need the presence of portlandite, produced during clinker hydration, for starting to react (7).…”

“…Numerosos trabajos (1,3,4) han demostrado que, expuestos a condiciones óptimas de laboratorio, los cementos que incorporan estas adiciones presentan un buen comportamiento en lo que a las propiedades en servicio se refiere, incluso mejor que el observado para el cemento Portland (5, 6). La escoria de alto horno posee propiedades hidráulicas, por lo que empezaría a reaccionar desde el momento del amasado, mientras que la ceniza volante posee propiedades puzolánicas, así que sus partículas necesitan la presencia de portlandita, formada en la hidratación del clínker, para comenzar a reaccionar (7).…”

Electrical Conductivity and Chloride Ingress in Hardened Cement Paste

“…McCarter et al (2000) reported that the electrical conductivity and permeability and the diffusion coefficient of mortar showed a good correlation, which shows the relationship between the electrical conductivity and other properties of cement-based materials. In addition, there have been many studies investigating the correlation between the electrical conductivity and other properties of concrete (Andrade 1993;Streicher and Alexander 1995;Sánchez et al 2011;Ortega et al 2012;Shi et al 1999;Díaz et al 2006;Mercado et al 2012;Buenfeld and Newman 1987;Shane et al 2000;Vedalakshmi et al 2008;Neithalath and Jain 2010;Minagawa et al 2010). However, most studies have investigated limited ranges of water to cement ratios (W/C 0.4-0.6), and the relationship between the porosity and conductivity of mortar or concrete, which includes the effect of the interfacial transition zone (ITZ), was established as shown in Table 1.…”

Impact of the pore solution on the aqueous diffusion through porous materials

“…Most techniques rely still today on saturated samples [1,[4][5][6][7][8][9][10][11]. Yet, in-situ structures are hardly encountered in saturated state.…”