INTRODUCTION
The corrosion performance of stainless steel clad reinforcing bar (SCR) was investigated. Corrosion potential of SCR in various alkaline media as a function of time was measured periodically and corrosion rates were estimated using Electrochemical Impedance Spectroscopy (EIS). At room temperature, SCR without cladding breaks was free of corrosion for up to one year in all the testing conditions: saturated Ca(OH)2 solutions (SCS, pH ~12.6), simulated pore solution (SPS, pH ~13.6), simulated carbonated concrete pore solution (CPS, pH <10) (each with 15 wt% chloride by the end of test), and concrete with chloride up to 8% chloride by weight of cement. SCR without cladding breaks also remained passive at 40 oC in SCS with 15% chloride and in concrete with 8% chloride. SCR with a 1 mm hole corroded actively in SCS with 15% chloride. The results suggest that carbon steel exposed by the small hole was corroding actively at a high local rate. A model for SCR with a single cladding break at one cut-end in concrete was modeled using a finite differences approach. Calculations indicated that the resistivity of concrete and size of cladding breaks were critical parameters in establishing the rate of corrosion, and that corrosion of SCR with sub-millimeter breaks in high quality concrete would cause concrete cracking only after long service times.
Austenitic stainless steel (SS) rebars have shown very promising corrosion performance in chloride-contaminated concrete (1-6) but at a higher cost than conventional plain carbon steel (CS) rebar. Stainless steel clad rebar (SCR) (7) with a carbon steel core offers the potential for performance comparable to that of solid SS rebar but at a much lower cost. However, SCR is vulnerable to corrosion at cladding breaks that may result from local mechanical damage or unprotected cut ends. Upon chloride contamination of the surrounding concrete, an intense galvanic couple may develop between the exposed carbon steel and the surrounding, still passive, stainless steel. These conditions can be especially promoted in marine service (8,9). The resulting extent of corrosion is a function of the amount of the base steel exposed and the surrounding stainless steel, the polarization characteristics of both, and the properties of the surrounding concrete. This work examined these issues by characterizing the corrosion behavior of SCR in the sound condition (no cladding breaks), and with intentionally introduced breaks, in various simulated concrete pore solutions and concrete to which controlled amounts of chloride ions were introduced. The results were input to a simplified model to estimate the extent of corrosion that may result from the corrosion macrocell between a small spot of carbon steel exposed at a cladding break and the rest of a reinforced concrete cylinder.
EXPERIMENTAL
Materials and Preparation
The Stainless Steel Clad Rebar (SCR) stock investigated was No.5 (16 mm diameter), corrugated, with a typical 0.8 mm thick cladding of Type 316L SS, and manufactured using the Nuovinox Process (7). Specimens, 5 or 10 cm long, were cut out for evaluation. Electric contact was made through copper wires placed at one end which then was covered by specially designed mortar caps to prevent crevice corrosion, which is otherwise frequently observed at the junction with an epoxy cap. The other end was terminated by one of the following methods: A, a proprietary stainless steel cap; B, a welding overlay; C, another mortar cap.
Methods A and B were to evaluate two proposed capping methods for SCR cut-ends in field construction. Method C was used to evaluate the behavior of the side surfaces without observing a crevice-corrosion effect. F
