Chloride ion penetration in concrete: The reaction factor in the electrical resistivity model

Several models have been published to calculate service life of reinforced concrete based on considering diffusion as the main ingress mechanism. However, these models have some limitations and involve destructive and time consuming testing. The authors have developed an alternative model based on electrical resistivity, which is a non-destructive test. When measured in concrete, electrical resistivity is an indication of its pore connectivity and also can be related to the concrete resistance to the penetration of gases and liquids. The main basis of the model has been already published. The present paper describes the calculation of the so-called “reaction or retardation factor” which is necessary for the model to take into account the amount of bound chlorides or carbon dioxide. The resistivity alone only appraises the available porosity which is equivalent to the effective diffusion coefficient. To consider the retardation in the ingress due to the chloride and carbon dioxide binding, it is necessary to include such an effect. In the model this is done by multiplying the resistivity measured at 28 days in water saturated concrete by a reaction factor, rb, which will give the “apparent resistivity” equivalent to the apparent diffusion coefficient rCl. The value of rCl is calculated from the ratio between effective and apparent diffusion coefficients. This paper gives such values for several cement types.