ABSTRACT

Various types of solid and coated reinforcing bars, including stainless steel types 316LN, 2205, 2201 and 3Cr12; a proprietary low-carbon, chromium alloy (ASTM A1035); epoxycoated both recently produced and 15-year old bars extracted from a northern bridge deck; and zinc-coated (galvanized), were simultaneously exposed to 5 % NaCl solution at 35°C in a salt-spray (fog) apparatus (ASTM B 117) for up to 4 weeks. Conventional carbon steel reinforcing bars were included as a control. The bar condition was visually inspected periodically and weight loss analyses were performed at 1, 2 and 4 weeks. Based on weight loss data, the corrosion resistance of the solid bars was ranked as follows: 316LN and 2205 > 2201 > 3Cr12 and A 1035 > carbon steel. Galvanized bars showed some delay in corrosion of the underlying steel, however, the zinc coating was quickly consumed and the average corrosion rate was comparable to that of carbon steel bars. In contrast, corrosion on all the epoxy-coated bars occurred only at defects and the average weight loss was nearly zero. The relative corrosion resistance ranking of the tested bars is consistent with the results reported in literature from more intensive testing regimes. Therefore, this highly accelerated test program provided a simple, quick, and useful comparison of the corrosion resistance of the tested steel reinforcement.

INTRODUCTION

Conventional carbon steel reinforcing bars are passive in normal concrete because the concrete provides a desirable high pH (~13) medium and also acts as a physical barrier isolating the steel from aggressive species, such as deicers, in the environment. However, black bars have low corrosion resistance and are vulnerable to corrosion when the pH is lost or when chloride ions penetrate the concrete cover. The corrosion products of steel in concrete occupy much more volume than the steel does and this introduces significant stresses in the surrounding concrete if the products accumulate. Soon afterward, distress such as cracks and spalling in the concrete occur and costly maintenance is required (1) According to a Federal Highway Administration (FHWA) report published in 2002(2), as shown in Figure 1, the annual U.S. infrastructure corrosion cost is $22.6 billion of which $8.3 billion is related to corrosion (and the consequent maintenance cost) of the estimated ~ 235,000 U.S. highway bridges constructed with traditional steel reinforced concrete. This estimate didn?t include indirect costs such as traffic delay, which could be as much as 10 times higher than the direct corrosion costs. In addition, this estimate was made based on data collected in late 1990s and the current corrosion cost could be even higher due to inflation. In the past several decades, many corrosion resistant reinforcing materials have been developed to address this corrosion issue. Examples of such materials are galvanized bar, epoxy-coated bar, various grades of stainless steel bars, and stainless steel clad bars.(3) In order to evaluate the corrosion resistance of these candidate materials, numerous laboratory testing programs have been performed which often used laboratory testing methods such as ASTM G 109 and the Southern Exposure. (4)

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