Corrosion of reinforcing steel evaluated by means of concrete resistivity measurements

By O’Hayre, Ryan; Lee, Sang-Joon; Cha, Suk-Won & Prinz, Fritz.B
Published in Corrosion Science NULL 2002

Abstract

The corrosion behaviour of reinforcing steel bars (rebars) in four different concrete mix designs commonly used at coastal cities in Argentina is studied. The investigation has two basic objectives: (1) to evaluate the influence of certain local variables that affect the rebar corrosion process, among which the common practice of using sea sand as a fine aggregate, exposure conditions and typical mix designs are the most important, and (2) to establish a rebar corrosion evaluation criterion based on measurements of concrete electrical resistivity. Two exposure conditions were investigated: seashore environment and partially immersed in a saline solution. Two water to cements and various chloride ions additions were selected for the study. Electrochemical parameters characteristic of the corrosion process were evaluated together with mechanical, chemical and physical properties of the concrete mixes. Rebars in contact with a good quality concrete (fc≈30 MPa) exposed for 1000 days to the seashore environment remained in the passive state, even when its surface chloride concentration reached 0.75% with respect to cement content. This behaviour was even better than that observed on a standard-quality uncontaminated concrete (fc≈20 MPa). When immersed in a saline solution, all rebar segments presented an active behaviour (Ecorr<-0.35 V vs. copper sulphate electrode and icorr>0.2 μA cm-2), although the CR depended primarily on the concrete quality and the initial chloride concentration. The electrical resistivity of concrete has proven to be an effective parameter to evaluate the risk of reinforcing steel corrosion independently of mix design and exposure condition. Rebars are likely to achieve an active state of corrosion when Ï? is lower than 10 kΩ cm, and likely to present a passive behaviour when concrete resistivity is higher than 30 kΩ cm.

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