Suitability of the Measurement Techniques of Oxygen Permeability in Order to Predict Corrosion Rates of Concrete Rebars

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Title: Suitability of the Measurement Techniques of Oxygen Permeability in Order to Predict Corrosion Rates of Concrete Rebars

Author(s): C. Andrade, C. Alonso, I. Rz-Maribona, and M. Garcia

Publication: Special Publication

Volume: 122

Issue:

Appears on pages(s): 45-60

Keywords: cement pastes; concretes; corrosion; measuring instruments; mortars (material); oxygen; permeability; reinforcing steels; Materials Research

Date: 6/1/1990

Abstract:
The air or oxygen permeability of concrete is usually measured by means of techniques that utilize mechanical driving forces. Thus, air or oxygen is forced to pass through a piece of concrete using different mechanical pressures. The flow of gas so measured is used as an indication of concrete permeability and sometimes is also used to predict the durability of concrete reinforcements based on the relationship between anodic corrosion rate and amount of oxygen, which may be reduced in the cathodic areas. However, this extrapolation may lead to erroneous conclusions, because a dry concrete allows a higher amount of oxygen to pass through it than a wet one, although the corrosion rate should be much lower in dry than in wet concrete. In this paper, comparisons between flow of oxygen measured in paste, mortar, and concrete specimens held at different relative humidities using electrochemical driving forces (polarization at about -750 mV SCE), and corrosion rates (measured by means of polarization resistance) are presented to discuss the inherent relationships. The results show that the oxygen permeability is only dependent on the amount of electrolyte inside the pores, but the corrosion rate is also dependent on the concrete resistivity, which is fixed by the amount of pore water content.