Testing of Selected Metallic Reinforcing Bars for Extending the Service Life of Concrete Bridges: Testing in Solutions

About the report:

Stainless steel-clad rebar provides an opportunity to significantly increase the Cl- threshold concentration associated with active corrosion initiation compared to plain carbon steel. However, threshold Cl- concentrations for 316L stainless steel-clad rebar are unknown. Moreover, the impact of possible galvanic corrosion between the clad layer and any exposed carbon steel core has not been investigated. The Cl- threshold concentrations for corrosion initiation on clad 316L stainless steel (with a thickness of about 1 mm over a carbon steel core), solid 316LN stainless steel, and plain carbon steel were examined in saturated Ca(OH)2 plus various concentrations of NaCl. The electrochemical properties of "intact" 316L stainless steel-clad rebar were found to be similar to those of solid 316LN stainless steel according to several electrochemical criteria. The Cl- threshold concentrations for corrosion initiation were increased to Cl-/OH- molar ratios as high as 17 to 24 even at high anodic potentials for "intact" 316L-clad and solid 316LN stainless steel, respectively. Thus, active corrosion of "intact" 316L-clad rebar could be delayed for many years due to the high Cl-/OH- molar ratios required at the stainless steel/concrete interface and the slow transport rate of chloride in concrete. In contrast, the threshold chloride concentration for corrosion initiation on carbon steel was low (Cl-/OH- molar ratio < 1.5) at all potentials. Cladding with a physical breech exhibited Cl-/OH- thresholds dominated by the exposed plain carbon steel. Galvanic coupling between exposed plain carbon steel and the stainless steel-cladding accelerated corrosion of the plain carbon steel only at and above the Cl-/OH- ratio necessary for corrosion initiation on carbon steel.

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