The corrosion resistance of EnduraMet® 32 stainless steel bars was evaluated using the rapid macrocell test outlined in Annexes A1 and A2 of ASTM A955-10. Based on the test results, the EnduraMet® 32 stainless steel bars satisfy the requirements of ASTM A955-10

Browning, JoAnn

Darwin, David

O’Reilly, Matthew

Sturgeon, W. Joseph

English

KU ScholarWorks

                                                           RAPID MACROCELL TESTS OF  ENDURAMET® 32 STAINLESS STEEL BARS     By W. Joseph Sturgeon Matthew O’Reilly David Darwin JoAnn Browning        A Report on Research Sponsored by   TALLEY METALS           Structural Engineering and Engineering Materials SL Report 10-5 November 2010 THE UNIVERSITY OF KANSAS CENTER FOR RESEARCH, INC. 2385 Irving Hill Road, Lawrence, Kansas 66045-7563     RAPID MACROCELL TESTS OF  ENDURAMET® 32 STAINLESS STEEL BARS     By   W. Joseph Sturgeon Matthew O’Reilly David Darwin JoAnn Browning       Research supported by  TALLEY METALS         Structural Engineering and Engineering Materials SL Report 10-5    THE UNIVERSITY OF KANSAS CENTER FOR RESEARCH, INC. LAWRENCE, KANSAS November 2010 ii   iii  ABSTRACT  The corrosion resistance of EnduraMet® 32 stainless steel bars was evaluated using the rapid macrocell test outlined in Annexes A1 and A2 of ASTM A955-10.  Based on the test results, the EnduraMet® 32 stainless steel bars satisfy the requirements of ASTM A955-10.                   Keywords: chlorides, concrete, corrosion, macrocell, reinforcing steel, stainless steel  iv  ACKNOWLEDGEMENTS  The research described in this report was supported by Talley Metals, Inc. 1  INTRODUCTION  This report describes the test procedures and results of rapid macrocell tests to evaluate the corrosion performance of EnduraMet® 32 stainless steel reinforcing bars.  Six specimens are tested in accordance with Annexes A1 and A2 of ASTM A955-10.   EXPERIMENTAL WORK Materials Tests were performed on No. 5 (No. 16) EnduraMet® 32 stainless steel bars.  The bars were inspected upon receipt and found to be in good condition.   The EnduraMet® 32 bars underwent pickling prior to shipment.  According to the supplier, pickling consists of 30 minutes in hot Cleanox, a product of Henkel Corporation, followed by five minutes in nitric acid.  Cleanox is a mixture of hydrofluoric and sulfuric acids with concentrations of 20g/L and 125g/L, respectively.  The bars are removed from the acid and rinsed using high-pressure water every 10 minutes while in Cleanox.  The temperature is maintained at 130°F for the duration of the process.    The chemical composition of the EnduraMet® 32 stainless steel is given in Table 1. Table 1: Chemical Composition of EnduraMet® 32 Stainless Steel (Provided by Manufacturer) Material Composition Report (%) Material Cr Ni C Mn N P S Mo Si Cu Co B EnduraMet® 32 17.8 0.74 0.05 12.2 0.29 0.019 0.001 0.18 0.29 0.07 0.03 0.0022  Experimental Procedures  Rapid Macrocell Test Six specimens were tested in accordance with the rapid macrocell test outlined in Annexes A1 and A2 of ASTM A955/A955M-10 and detailed in Figure 1.  Each bar used in the  2  Scrubbed airSalt bridgeLidLidSimulated PoreSolutionTerminal BoxVoltmeterSimulated PoreSolution with NaClV10 OhmAnode Cathoderapid macrocell is 5 in. long and is drilled and tapped at one end to accept a 0.5-in., 10-24, stainless steel machine screw.  Bars are cleaned prior to testing with acetone to remove oil and surface contaminants introduced by machining.  A length of 16-gauge insulated copper wire is attached to each bar via the machine screw.  The electrical connection is coated with an epoxy to protect the wire from corrosion. A single rapid macrocell specimen consists of an anode and a cathode.  The cathode consists of two bars submerged to a depth of 3 in. in simulated pore solution in a plastic container, as shown in Figure 1.  One liter of pore solution consists of 974.8 g of distilled water, 18.81 g of potassium hydroxide (KOH), and 17.87 g of sodium hydroxide (NaOH).  The solution has a pH of about 13.4.  Air, scrubbed to remove carbon dioxide, is bubbled into the cathode solution.  The anode consists of a single bar submerged to a depth of 3 in. in a solution consisting of simulated pore solution and 15 percent sodium chloride (NaCl).             Figure 1: Rapid Macrocell Test Setup   3  The “salt” solution is prepared by adding 172.1 g of NaCl to one liter of pore solution.  The solutions are changed every five weeks to limit the effects of carbonation.  The anode and cathode are connected electrically across a 10-ohm resistor.  A potassium chloride (KCl) salt bridge provides an ionic connection between the anode and the cathode (Figure 1). The corrosion rate is calculated based on the voltage drop across the 10-ohm resistor using Faraday’s equation.   Rate V mKn F D R A⋅=⋅ ⋅ ⋅ ⋅            (1) where the Rate is given in μm/yr, and K = conversion factor = 31.5·104 amp·μm ·sec/μA·cm·yr V = measured voltage drop across resistor, millivolts m = atomic weight of the metal (for iron, m = 55.8 g/g-atom) n = number of ion equivalents exchanged (for iron, n = 2 equivalents) F = Faraday’s constant = 96485 coulombs/equivalent D = density of the metal, g/cm3 (for iron, D = 7.87 g/cm3) R = resistance of resistor, ohms = 10 ohms for the test A = surface area of anode exposed to solution, 39.9 cm2 Using the values listed above, the corrosion rate simplifies to:                               Rate 29 0= . V       (2)                        To satisfy ASTM A955, no individual corrosion rate may exceed 0.50 μm/yr and the average rate of all specimens may not exceed 0.25 μm/yr.  In both cases, the corrosion current must be such as to indicate net corrosion at the anode.  Current indicating a “negative” value of corrosion, independent of value, does not indicate corrosion of the anode and is caused by minor differences in oxidation rate between the single anode bar and the two cathode bars.  4  In addition to the corrosion rate, the corrosion potential is measured at the anode and cathode using a saturated calomel electrode (SCE).  Readings are taken daily for the first week and weekly thereafter.    RESULTS  The individual corrosion rates of the six specimens tested are shown in Figure 2, and the overall average corrosion rate for all six specimens is shown in Figure 3.  Throughout the duration of the test, no individual specimen exhibited a positive corrosion rate.  The average corrosion rate ranged from 0 to –0.400 μm/yr with a maximum negative corrosion rate of –1.285 μm/yr for specimen 4 in week 8 of the test.  As shown in Figure 3, the average corrosion rate was negative and was close to –0.300 μm/yr throughout most of the test.  “Negative” corrosion is caused by minor differences in oxidation rate between the single anode bar and the two cathode bars. Thus, no individual specimen or the average exhibits a positive corrosion rate.  Therefore, the individual specimens and the average are below the allowable maximums of 0.50 μm/yr and 0.25 μm/yr, respectively.   Individual corrosion potential data taken with respect to a saturated calomel electrode (SCE) for the bars in pore solution with salt (anode) and bars in pore solution (cathode) are shown in Figures 4 and 5, respectively.  As shown in Figure 4, the bars in pore solution plus salt show potentials ranging from −0.100 to −0.200 V verses the SCE.  The bars in pore solution have potentials, shown in Figure 5, within the range of −0.100 to −0.300 V.  ASTM C876 states that a potential more negative than −0.275 V with respect to an SCE (−0.350 with respect to a copper/copper sulfate electrode) indicates a 90% probability that corrosion is occurring.  Two   5             Figure 2:  Individual corrosion rate of EnduraMet® 32 stainless steel, Specimens 1-6.           Figure 3:  Average corrosion rate of EnduraMet® 32 stainless steel, Specimens 1-6.  important differences between this macrocell test and ASTM C876 prevent a direct comparison of this test to ASTM C876: the bars being tested are stainless steel, not a conventional steel -1.40-1.20-1.00-0.80-0.60-0.40-0.200.000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Time (weeks)Corrosion Rate (µm/yr)..  .M-N32_R2-1 M-N32_R2-2 M-N32_R2-3M-N32_R2-4 M-N32_R2-5 M-N32_R2-6-1.40-1.20-1.00-0.80-0.60-0.40-0.200.000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Time (weeks)Corrosion Rate (µm/yr)..  . 6  alloy, and they are placed in a pore solution, not concrete.  Overall, the average potentials, shown in Figure 6, are more negative for bars in pore solution than for bars in pore solution plus salt by 0.050 to 0.075 V throughout the test.  This further explains the negative corrosion values.   Specimen 4 exhibited the most negative corrosion rate in week 8, which is drastically more negative than the rest of the specimens.  As shown in Figures 4 and 5, its anode potential falls in line with the other specimens.  However, the cathode potential of specimen 4 is much more negative than the remaining specimens and peaks at about week 8 as well.  The cathode potential at the peak is nearly 0.150 V more negative than the anode and would explain the large negative corrosion rate.                     Figure 4:  Individual corrosion potential with respect to SCE.  EnduraMet® 32 stainless steel bars in salt solution (anode), specimens 1-6.     -0.350-0.300-0.250-0.200-0.150-0.100-0.0500.0000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Time (weeks)Corrosion Potential (V)M-N32_R2-1 M-N32_R2-2 M-N32_R2-3M-N32_R2-4 M-N32_R2-5 M-N32_R2-6 7             Figure 5:  Individual corrosion potential with respect to SCE.  EnduraMet® 32 stainless steel bars in pore solution (cathode), specimens 1-6.                 Figure 6:  Average corrosion potential with respect to SCE.  EnduraMet® 32 stainless steel bars, specimens 1-6.  -0.350-0.300-0.250-0.200-0.150-0.100-0.0500.0000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Time (weeks)Corrosion Potential (V)Average Anode Potential Average Cathode Potential-0.350-0.300-0.250-0.200-0.150-0.100-0.0500.0000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Time (weeks)Corrosion Potential (V)M-N32_R2-1 M-N32_R2-2 M-N32_R2-3M-N32_R2-4 M-N32_R2-5 M-N32_R2-6 8  Once the specimens reached week 15, the test was terminated, and the specimens were removed from solution, rinsed with tap water, examined for corrosion, and photographed.  All six specimens looked relatively clean along the length of the bar upon removal from solution.    SUMMARY AND CONCLUSIONS The corrosion resistance of EnduraMet® 32 stainless steel bars was tested in accordance with Annexes A1 and A2 of ASTM 955-10.  The following conclusion is based on the test results presented in this report:   The EnduraMet® 32 stainless steel bars tested in this study satisfy the requirements specified in Annexes A1 and A2 of ASTM 955-10.    9  REFERENCES ASTM A955, 2010, “Standard Specification for Plain and Deformed Stainless-Steel Bars for Concrete Reinforcement (ASTM A955/A955M-10),” ASTM International, West Conshohocken, PA, 11 pp.  ASTM C876, 2009, “Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete (ASTM C876-09),” ASTM International, West Conshohocken, PA, 7 pp.      

Rapid Macrocell Tests of Enduramet® 32 Stainless Steel Bars

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Rapid Macrocell Tests of Enduramet® 32 Stainless Steel Bars

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