Measurement of Corrosion of Steel Reinforcement Under High Chloride Conditions

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Title: Measurement of Corrosion of Steel Reinforcement Under High Chloride Conditions

Author(s): D. Baweja, H. Roper, S. Guirguis, and V. Sirivivatnanon

Publication: Special Publication

Volume: 132

Issue:

Appears on pages(s): 1543-1564

Keywords: blast furnace slag; chlorides; corrosion; durability; fly ash; half-cell potential; marine atmospheres; polarization; reinforcing steels; Materials Research

Date: 5/1/1992

Abstract:
The background to a major study into the corrosion characteristics of steel reinforcement within portland and blended cement concretes is presented. The objectives of this work included an investigation into relationships between chloride-ion concentration and the onset and rate of steel corrosion in concrete. Corrosion activity of steel reinforcement within concrete specimens was measured using procedures including half-cell potential, resistivity, and potentiodynamic anodic polarization. A total of four binder types that included a slag-blended cement and a fly ash-blended cement were used. Chlorides were introduced into the concrete specimens subsequent to casting and curing by partial immersion into salt solutions. The development of a procedure to electrochemically measure the corrosion rate of steel in concrete slab specimens partially immersed in chloride solutions is described. Some of the data obtained using this procedure are discussed in relation to measured half-cell potentials for slab specimens. Based on information available to date, assessments were made regarding the relative marine durability performance of the various binder types considered. Obtained half-cell potential data were analyzed with respect to the time taken to reach -350 mV (versus Cu/CuSO 4), a value where there is a 95 percent probability of corrosion activity as defined by ASTM C 876. Using statistically based procedures, it was found that concrete water-binder ratio was the major influence on the time taken for half-cell potentials to reach -350 mV. The binder type also had a significant influence on the time taken for potentials to reach -350 mV. Considering concretes cast at equal water-binder ratios, half-cell potentials for reinforcement with slag-blended cement concretes took longer to reach -350 mV when compared with other binders tested.