Bridges for Service Life Beyond 100 Years: Innovative Systems, Subsystems, and Components (2014)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

209 A p p e n d i x e Background Delaying the onset of corrosion is one of the most important factors determining the service life of a reinforced concrete structure. Corrosion-resistant structures can be achieved by preventing salt from penetrating to the level of the reinforcing steel, by using corrosion-resistant reinforcement, or by using both of these techniques simultaneously. Research has shown that the corrosion resistance of various types of reinforcing bars is dependent on the type of bar and the handling and treatment of the bars before and after concrete placement. Studies have shown that electrochemical treatment may increase corrosion resistance by up to 10 times (Glass and Reddy 2002). Problem Statement Over the past decades, the principal techniques for corrosion prevention in bridge decks have included increased concrete cover to slow the intrusion of chlorides from salts or ocean spray to the level of reinforcement and the application of epoxy coating over the steel reinforcement to protect the steel from chlorides and corrosion. However, increased concrete cover depth increases both dead load and construction costs, and it does not eliminate the occurrence of cracks, which facilitate the intrusion of chlorides. Epoxy coating limits the expo- sure of the steel to chlorides, oxygen, and moisture and adds nominally to bridge construction costs. However, holes and breaks in the epoxy coating, in combination with high chloride concentrations, can result in corrosion of the steel reinforcement. Moreover, epoxy coating in aging bridge decks may become brittle and eventually delaminate from the steel reinforcement. Dense (low-permeability) concretes, corrosion inhibitors, and both nonmetallic and steel-alloy corrosion-resistant rein- forcement are among the most common techniques being considered as alternative measures for mitigating corrosion in reinforced concrete structures. This research topic evaluated means of achieving corrosion resistance in concrete reinforced with conventional reinforcing steel by pretreating the concrete electrochemically. For com- parison, stainless steel (316LN) and titanium bars were used that are known to have high corrosion resistance. This research was built on work completed to date, including work sponsored by the Federal Highway Administration (FHWA) (Hartt et al. 2006, 2009). Description of the Concept Reinforced concrete structures that can tolerate a higher level of chlorides before corrosion initiates will provide longer service lives. If the critical chloride threshold of conventional steel can be increased to a level close to or equal to stainless steel (316LN), service lives greater than 100 years may be achievable with conventional cover depth and low-permeability concretes. Corrosion-Resistant Reinforcement Titanium would extend time-to-corrosion cracking by about 130 times compared with black bars (Gong et al. 2006). However, its initial cost in today’s market is five times that of stainless steel. Stainless steel contains a minimum of 12% chromium, which creates an invisible film that helps resist oxidation. The chloride threshold is at least 10 times greater than carbon steel (Gong et al. 2006). A 65-plus-year-old bridge in the Gulf of Mexico with 304 stainless steel reinforcement is showing that it is possible to achieve 100 years of service life (Arminox 1999). Electrochemical Treatment Electrochemical treatments involve the application of a direct current for a period of time sufficient to change the environ- ment around the reinforcing steel. The two most common electrochemical treatments used on reinforced concrete Improving the Corrosion Resistance of Conventional Reinforcement

210 structures are electrochemical chloride extraction (ECE) and realkalization. Electrochemical treatments can be used to migrate ions such as chlorides out of concrete, as in the case of ECE. Realkalization and other electrochemical treatments can also be used to increase the pH of concrete. The purpose of these electrochemical treatments is to create a passive, noncorroding environment around the reinforcing steel. Objectives of the Research The main objective of this research was to determine the corro- sion resistance of electrochemically treated concrete with black bar and compare it with the resistance of untreated concrete with black bar and corrosion-resistant material. Corrosion- resistant materials used for comparison included commercially available stainless steel rebar (316LN) and titanium bar. The corrosion resistance of treated and untreated concrete samples was compared with the performance of conventional black reinforcing steel and corrosion-resistant reinforcement. Research Approach Introduction To increase the chloride threshold level (thus, the corrosion resistance) in reinforced concrete structures with conventional reinforcing steel, electrochemical treatment was applied in both low and high levels. Organization and Conduct of the Research Reinforced concrete specimens with different levels of pre- treatment were prepared and tested to determine their critical chloride (corrosion initiation) threshold. The electrochemical treatment was applied at low and high levels of pretreatment to increase the threshold level of black bars (mild steel). The following list of tasks describes how the research team accomplished the project objectives: Task 1. Summarize the literature on studies of different steel reinforcement. Task 2. Obtain material and equipment to be used during the testing stage. Task 3. Fabricate specimens with the selected reinforcement (mild steel [black bar], stainless steel, or titanium). Task 4. Conduct the electrochemical treatment on a selected number of test specimens with mild reinforcement. Task 5. Apply cycles of wetting and drying periods. The wet stage had chloride solution ponded over the specimens. Task 6. Monitor the samples by measuring the macrocell cur- rent and half-cell potential. Analyze the results and provide new recommendations. Task 7. Prepare the final report and recommendations. Analysis of Available data A literature survey on different corrosion-resistant reinforce- ments and electrochemical treatments was conducted. A summary of the literature on titanium reinforcing bars, stain- less steel reinforcement, and electrochemical treatments is included here. Titanium Reinforcing Bars Titanium is a corrosion-resistant material that could potentially be used in transportation structures as a primary reinforcement to extend service life with minimal maintenance; however, the cost of titanium is currently as much as five times that of stain- less steel. Froes et al. (2007) report that 1 lb of carbon steel ingot and 1 lb of titanium cost $0.15 and $9.07, respectively. • Titanium is lighter than stainless steel, has similar strengths, and has lower coefficients of thermal expansion and elastic modulus. Its properties are as follows (Donachie 2000; Metals Handbook 1998). • The relative density is 4.51. • The coefficient of linear expansion is 5.0 in. × 10-6 in. per in./°F. • The tensile strength of elemental titanium is 35 ksi, but it can be as high as 180 ksi with titanium alloys. • The modulus of elasticity is 17 × 106 psi. Titanium (ASTM B348 2011a) metal’s corrosion resistance is due to a stable, protective, strongly adherent oxide film (TIMET 1999). This film forms instantly when a fresh surface is exposed to air or moisture. The oxide layer increases in thickness with time, reaching 250 Å in 4 years. The film growth is accelerated under strongly oxidizing conditions, such as heating in air, anodic polarization in an electrolyte, or exposure to oxidizing agents. The composition of this film varies from TiO2 at the surface to Ti2O3 to TiO at the metal interface. The oxide film on titanium is very stable and is attacked by only a few substances, most notably hydrofluoric acid. Titanium is capable of healing this film almost instantly in any environment in which a trace of moisture or oxygen is present. Anhydrous conditions in the absence of a source of oxygen should be avoided because the protective film may not be regenerated if damaged. Titanium has excellent resistance to corrosion by neutral chloride solu- tions, even at relatively high temperatures. Titanium and its alloys may be affected in aqueous chloride environments by crevice corrosion. Stainless Steel Reinforcement The term stainless steel refers to a group of corrosion-resistant steels that contain a minimum of 12% chromium (Scully and Hurley 2007). The chromium creates an invisible surface film

211 that helps stainless steel resist oxidation. Other metals can be added to increase corrosion resistance. Various grades of stainless steels have been developed for use as reinforcement in concrete to resist chloride environments. Stainless steel reinforcements are available as solid bars or stain- less steel–clad bars. Stainless steel offers many advantages: • Chloride threshold values for stainless steel have been reported to be at least 10 times greater than for carbon steel (Clemeña 2003; Gong et al. 2006). • Stainless steel has inherent corrosion resistance and does not require the aid of other corrosion protection methods, such as cathodic protection or corrosion inhibitors. • Stainless steel has good strength and ductility, and many of the commonly used grades also exhibit good weldability. • Solid stainless steel bars can withstand shipping, handling, and bending without the danger of damage to the coating. • Exposed ends are not a problem in solid stainless steel bars and do not have to be repaired as they do in stainless steel– clad bars (Smith and Tullmin 1999). Solid stainless steel is used in Europe rather than stainless steel–clad carbon steel because the process of fusing the two types of metal together is not considered cost-effective. Another advantage of solid stainless steel bars is that they can be shipped, handled, and bent without fear of damage to the coating. In addition, the ends do not have to be coated after cutting (NCHRP 2004). Stainless steel is often used in areas where sufficient cover cannot be obtained or at construction joints and critical gaps between columns and decks. Because of the cost of stainless steel, estimated to be four to six times more than black bar, many engineers do not expect it to become a standard for all reinforcement (Nürnberger 1996). Gong et al. (2002) compared the costs of different types of reinforcement in a thick deck. They reported an initial cost of deck area for stainless steel was approximately 1.4 times more expensive than conventional reinforcement. However, based on total costs over 75 years, the stainless steel reinforcement was more economical. The types of stainless steel reinforcement that have been most commonly used are types 304, 316, and 316LN. All three types are austenitic stainless steel (Smith and Tullmin 1999). The FHWA report Corrosion Evaluation of Epoxy-Coated, Metallic-Clad, and Solid Metallic Reinforcing Bars in Concrete (McDonald et al. 1998) looked at two types of solid stainless steel in concrete exposure specimens, Types 304 and 316 (ASTM A955 2011b). The results show that the lowest corrosion rates for Type 304 bars were obtained when the stainless steel was used in both mats. Cracks in the concrete did not appear to affect the performance of the bars. Half the bars from specimens that contained black steel in the bottom mat exhibited moderate to high corrosion currents and had red rust on them. When the stainless steel bars were used in both mats, the specimens did not exhibit any signs of chloride-induced corrosion, even when the slabs were precracked (McDonald et al. 1998). McDonald et al. (1998) reported that all specimens contain- ing Type 316 solid stainless steel showed good corrosion per- formance. There was no distinguishable difference between precracked and uncracked slabs or between slabs with a black steel cathode or a stainless steel cathode. Measured corrosion for all conditions was about 800 times lower than that of the black steel specimens. During visual inspection of the slabs, only one of the bars exhibited corrosion, and it was considered to be minor. Both types of stainless steel, Types 304 and 316, were able to tolerate chloride levels much higher than the threshold level of black steel before the initiation of corrosion, especially when both mats were stainless steel. The threshold for Type 304 stain- less steel with a stainless steel cathode was 7 to 18 kg/m3 (which is 12 to 30 lb/yd3). For Type 316 stainless steel in both mats, the chloride concentration threshold ranged from 12 to 20 kg/m3 (which is 20 to 33 lb/yd3). Even when the stainless steel bars were coupled to black steel cathodes, the chloride concentration for the initiation of corrosion was still about twice that of black steel for Type 304 and 15 times the threshold of black steel for Type 316. The results from the study indicated that Type 316 stainless steel bars may be better than Type 304 bars for use in concrete because they are less susceptible to galvanic effects if they are coupled to carbon steel bars (McDonald et al. 1998). Stainless steel and stainless steel–clad reinforcement have been used in a number of structures in the past 25 years, but none of these structures is old enough that corrosion damage would be expected, even if no protection measures had been used. So far, stainless steel reinforcement is performing satisfac- torily. For example, in 1984, Type 304 stainless steel reinforcing bars were installed in part of a bridge deck north of Detroit, Michigan. The rest of the bridge was built using epoxy-coated steel. The deck was inspected and cores were removed in 1993 by Michigan Department of Transportation officials. No delaminations or corrosion-induced cracks were present on the deck. Two of the cores had longitudinal cracks (from tempera- ture and shrinkage) that intersected the reinforcing steel, but no evidence of corrosion was found, except for minor staining on one bar at the crack location. The chloride ion concentrations had approached the corrosion threshold for black steel, but had not exceeded it significantly (McDonald et al. 1998). The actual costs of three bridge projects that were con- structed in Illinois in 1994 with black or epoxy-coated steel (or both) were compared with what the costs would have been, according to industry experts, had stainless steel or titanium reinforcement been used. The use of epoxy-coated reinforcement had very little effect on the overall price of the projects, but stainless steel would have increased the

212 total cost by 5.5% to 15.6%. Titanium would have increased the total bridge cost by 35% to 90% (McDonald et al. 1995). Results from both field and laboratory studies of stainless steel as a corrosion-resistant reinforcement have been prom- ising. Stainless steel exhibits excellent corrosion resistance in severe corrosion environments. No corrosion-induced dam- age was reported in any of the studies reviewed for this report. A 1994 report indicated that stainless steel should extend the time-to-corrosion in reinforced concrete structures by 65 to 130 times compared with black steel. When long-term dura- bility is important, the extra cost of using stainless steel appears to be justified by the expected service life extension provided (McDonald et al. 1995). An outstanding example of a stainless steel–reinforced bridge is the Progreso Pier in the Gulf of Mexico. The bridge is a 2.2-km-long concrete pier leading out into the Gulf of Mex- ico, built in the 1940s and still operating today. The structure used the equivalent of 304 steel to reinforce the arches of the pier. Despite the harsh environment, combined with relatively high porosity and some casting defects in the concrete, no sig- nificant corrosion problems have been observed (Arminox 1999). The chloride levels at the surface of the reinforcement were more than 20 times the traditionally assumed corrosion threshold level. Based on the condition and aging of the pier, and the limited number of investigations carried out, it appears that a 100-year service life is possible with stainless steel. Electrochemical Treatment Electrochemical treatments can be applied to concrete struc- tures containing reinforcement to remove chlorides from the concrete (ECE) or to increase the pH of carbonated concrete (realkalization). Electrochemical treatments involve the applica- tion of current to cause changes in the chemistry of the con- crete. The steel, which acts like a cathode, is connected to the negative pole of a direct current power source. The anode, which is typically either steel or a titanium mesh, is temporarily placed on the concrete surface and is connected to the positive pole of the power source. An electrolyte is placed on the concrete and allows the current to flow. Due to the applied electric field, nega- tively charged ions, like chlorides, migrate from the rebar toward the surface and out of the concrete. At the same time, the passage of current through the system generates hydroxyl ions (OH-) at the steel–concrete interface, increasing the pH of the concrete. Studies indicate that electrochemical treatments can suc- cessfully remove substantial amounts of chloride from con- taminated concrete and lead to an increase in the pH of the concrete and repassivation of corroding reinforcing steel (Kepler et al. 2000). Studies have indicated that adverse side effects can be avoided as long as current densities are kept below 5 A/m2 of concrete surface (Bennett et al. 1993). Studies have demonstrated that a current density of less than 1 A/m2 of concrete surface is sufficient for treatment (Clem- eña and Jackson 1997; Manning and Ip 1994). The first elec- trochemical treatment (ECE) application to a bridge in North America was completed in 1989. The treated sections remain passive (noncorroding). No additional corrosion damage has occurred to date. Electrochemical treatments have been used to provide cor- rosion protection for structures suffering from chloride con- tamination, as well as carbonation. Research indicates that electrochemical treatments can be applied to new structures to increase long-term corrosion resistance by increasing the chloride corrosion threshold value potentially to the point that concrete completely saturated in salt water will not cor- rode. The increased tolerance to chlorides is believed to be primarily due to the increased alkalinity at the vicinity of the steel (Glass and Reddy 2002). The migration of alkali ions to the steel–concrete interface induces the precipitation of alka- line compounds that can block existing defects and large pores. It is known that corrosion on the surface of the steel reinforcement in the presence of chlorides initiates at such defects and pores, so their reduction in size below a certain critical size substantially increases resistance to corrosion. The subject research is exploring such a possibility. Conclusions and Findings A survey of existing literature indicated that proper stainless steel (e.g., 304 and 316LN) and titanium are expected to pro- vide satisfactory corrosion resistance and extend the service life of structures. The literature survey also indicated that electrochemical treatment of black bars in reinforced concrete may provide improved corrosion resistance and extend the service life of reinforced concrete structures. experimental program Testing Facility All specimens were prepared at the University of Nebraska– Lincoln at the civil engineering laboratory. Specimen Preparation Reinforced concrete specimens were prepared in the labora- tory and subjected to an accelerated testing regime under controlled conditions. The corrosion resistance of each com- bination within the test matrix was compared. All specimens were prepared and tested in triplicate to provide statistically significant results. The test matrix included conventional reinforcing steel (black bar), black bar with two levels of electrochemical treat- ment, stainless steel bar, and titanium bar.

213 Test Setup The specimen preparation and testing procedure considered to test the different matrices followed ASTM G109 (ASTM G109 2007a). Figure E.1 shows a three-dimensional view of a test specimen. Five variables were evaluated; different bars were placed in conventional concrete: • Black bars in untreated concrete (control); • Black bars in concrete subjected to low electrochemical treatment; • Black bars in concrete subjected to high electrochemical treatment; • Stainless steel (316LN) in untreated concrete; and • Titanium bars in untreated concrete. Three specimens of each variable were prepared (15 spec- imens total). Figure E.2 shows the measurements of the specimens. Materials The list of materials used is described and illustrated below. • Concrete was supplied by Concrete Industries Inc., a Lincoln, Nebraska, ready-mix concrete company, which provided the concrete on August 8, 2010. • Steel reinforcement was as follows (see Figure E.3): 44 27 Mild steel rebars (black bars), Grade 60, 0.5-in. diameter (No. 4) and 14 in. long; 44 Nine stainless steel rebars, Type 316LN, 0.5-in. diameter (No. 4) and 14 in. long; and 44 Nine titanium rods, Grade 2, 0.5-in. diameter and 14 in. long. • Stainless steel screws and nuts 44 45 Stainless steel screws (one per bar) with a diameter smaller than the bar diameter (coarse thread <0.2 in.), 1 to 1.5 in. long; and 44 90 Stainless steel nuts (two per bar) to fit the screws; • Two-part waterproof epoxy that met the resistance require- ments by ASTM C881 for a Type IV, Grade 2, Class E speci- fication epoxy (ASTM C881 2010); • Heat-shrink tube with internal adhesive (see Figure E.4). • Electroplater tape (not needed if heat-shrink tube is used). • Neoprene tubing (not needed if heat-shrink tube is used) with 0.125-in. wall thickness and same inner diameter as the diameter of the bar. • Sodium chloride. • Salt solution prepared by dissolving three parts of sodium chloride in 97 parts of water by mass. • Epoxy sealer for application to the concrete specimen after manufacture. Type III, Grade 1, Class C epoxy sealer was used in accordance with ASTM specifications (ASTM C881 2010). • Plastic dams measuring 3 in. wide and 6 in. long with a min- imum height of 3 in. and a wall thickness ±0.125 in. for placement on the test specimen. • Silicone caulk for sealing the outside of the plastic dam to the top of the concrete. • Reference electrode, such as saturated calomel or silver– silver chloride electrode for measuring the corrosion potential. • Hexane to wash the sandblasted reinforcements. • Multimeter to measure the macrocell voltage between electrode and rebars. Casting of Specimen The concrete samples were prepared in compliance with ASTM G109 (2007a). The samples were prepared according to the following instructions: 1. The rebars were cleaned by sandblasting to near white metal, after which they were soaked in hexane and air dried. Figure E.5 shows sample bars before and after sandblasting. 2. One end of each bar was drilled and tapped with a stainless steel screw and two nuts. At both ends of each rebar a 2-in.-long piece of heat-shrink tubing was placed so that 8 in. of bar remained bare. The rebar lengths pro- truding from the form were coated with two-part epoxy. Figure E.6 shows the application of heat-shrink tubing and the epoxy coating.Figure E.1. Three-dimensional view of test specimen.

214 (a) (b) Figure E.2. (a) Front and (b) top views showing dimensions of specimens for corrosion-resistance testing. Green area in front view is a dam. (a) (b) (c) Figure E.3. Steel reinforcement: (a) black bars, (b) stainless steel rebars, and (c) titanium rods.

215 3. Wooden forms measuring 11 × 6 × 4.5 in. were fabricated (see Figure E.7a). To facilitate form removal, oil was used on the form surface. 4. The rebar was placed so that approximately 2 in. of it projected from the form. This 2-in. section was taped to isolate it from the environment, leaving 8 in. of the rebar inside the concrete exposed to chlorides. The clear cover of concrete was 0.75 in. for the top rebar. Figure E.8 shows samples ready for concrete placement. 5. The concrete used was made in accordance with ASTM specifications (ASTM C192 2007b). A local ready-mix company delivered the concrete to the structural labora- tory at the University of Nebraska–Lincoln. The concrete had a water–cement ratio equal to 0.5, a cement content of 600 lb/yd3, air content of 5%, and minimum slump of 2 in. After placement and consolidation, the top surface Figure E.4. Heat-shrink tube. (a) (b) Figure E.5. Samples of (a) black bar and (b) stainless steel and titanium rebars before and after sandblasting. (a) (b) Figure E.6. (a) Application of heat-shrink tubing and (b) rebars after receiving epoxy coating.

216 was finished with a wood float. Figure E.9 shows samples before and after concrete pour. 6. A plastic sheet was used to prevent moisture loss (see Fig- ure E.10a); the forms were removed 4 days after casting. 7. After the forms were removed, electrochemical treat- ments were conducted on selected specimens. In the low- level ECE treatment, each specimen received a current of 8.1 mA for a period of 28 h. For the high-level electro- chemical treatment, each specimen received a current of 16.2 mA for a period of 28 h (see Figure E.11). 8. To prevent the electrochemical solution from becoming too acidic, lime (calcium hydroxide) was added. A tita- nium mesh was placed at the bottom of the plastic dam and later connected to the positive pole of the power supply. The rebars were connected to the negative pole. Multimeters were used to measure the amount of cur- rent flowing to each sample. Figure E.12 shows the three principal stages of ECE treatment. 9. The specimens were cured for 28 days at ambient tem- perature. At the conclusion of the curing period, the top (wood-floated) surface was wire brushed. The specimens were allowed to dry for 2 weeks before the four vertical sides were coated with an epoxy sealer. 10. The plastic dam was placed and sealed with silicone caulk. Finally, an epoxy sealer was applied to the region outside the dam (top surface only). The top rebar was connected (a) (b) Figure E.7. (a) Wooden forms before and (b) after application of oil. (a) (b) Figure E.8. Samples ready for concrete placement: (a) three samples with one variable and (b) all 15 samples.

217 (a) (b) Figure E.11. Electrochemical treatment readings at (a) low and (b) high levels. (a) (b) Figure E.10. (a) Samples covered by plastic to retain moisture and (b) sample removal from the wooden form. (a) (b) Figure E.9. (a) Concrete being placed into forms and (b) samples after wood-float finishing.

218 to the two bottom bars through a wire and one 100-W resistor. Figure E.13 shows the specimens prepared for the wet–dry cycle. Testing Procedure After discussion and literature review, the team decided to slightly change the length of the wet–dry cycle specified in ASTM G109 (ASTM 2007a). The short cycle selected was intended to optimize and therefore accelerate the corrosion of the rebars. The testing was conducted as follows: 1. Each sample was placed on two nonelectrically conduct- ing supports. The first reading was taken 1 month after the specimens were cast. 2. The specimens were ponded with a salt solution (approx- imately 400 mL at a depth of 1.5 in.) for 4 days. A loose- fitting plastic cover was used to minimize evaporation. After 4 days, the salt solution was vacuumed off (see Figure E.14), and the specimens were allowed to dry for 10 days. The cycle was repeated until the termination of the test program. 3. The voltage across the resistor between the top and bot- tom bars was measured by a voltmeter, and the corrosion potential was measured by a half-cell system (see Fig- ure E.15) with a silver–silver chloride electrode. Mea- surements were taken before ponding with the salt solution, after removal of the solution, and in the middle of the dry cycle. 4. The test was to be terminated when the integrated macro- cell current was equal to or greater than 150 C, which is equivalent to a macrocell current of 10 µA as specified by ASTM G109 (ASTM G109 2007a). Test Results The concrete had a compressive strength of 4,830 psi, which was an average of three cylinders. Due to time constraints, the testing was terminated after 26 cycles. Table E.1 shows (a) (b) (c) Figure E.12. Three principal stages of ECE: (a) before, (b) during, and (c) after electrochemical treatment. Figure E.13. Specimens ready to start the wet–dry cycle. Figure E.14. The salt solution was removed by vacuuming after the wet period was finished.

219 the summary of labels given to each specimen. Five vari- ables were considered for testing, and three identical speci- mens for each variable were made to provide statistical significance. The initial reading was taken on September 23, 2010 (Day 0). The samples were then subjected to successive cycles of 4 days wet and 10 days dry. At the end of each dry cycle, corrosion potential and current across resistor read- ings were taken for each specimen. Although not required by ASTM G109 (ASTM G109 2007a), additional readings were conducted at the end of each wet cycle and at the middle of each dry cycle. Half-Cell Potential Data Figure E.16 shows the half-cell potential readings for all specimens varying with time. The potential values were more positive than -0.20 V, indi- cating that there was a greater than 90% probability that no reinforcing steel corrosion was occurring, except with three Figure E.15. Measuring the half-cell potential. Table E.1. Samples Summary Label Type of Reinforcement Type of Treatment BB_1 BB_2 BB_3 Black bar Black bar Black bar None None None ECL_1 ECL_2 ECL_3 Black bar Black bar Black bar Low level of electrochemical treatment Low level of electrochemical treatment Low level of electrochemical treatment ECH_1 ECH_2 ECH_3 Black bar Black bar Black bar High level of electrochemical treatment High level of electrochemical treatment High level of electrochemical treatment SS_1 SS_2 SS_3 Stainless steel 316LN Stainless steel 316LN Stainless steel 316LN None None None Ti_1 Ti_2 Ti_3 Titanium Titanium Titanium None None None Figure E.16. Half-cell potential for all 15 specimens. 350 300 250 200 150 100 50 0 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 Co rr os io n Po te n ti al (m V ) Time (weeks) Half-cell potential BB_1 BB_2 BB_3 ECL_1 ECL_2 ECL_3 ECH_1 ECH_2 ECH_3 SS_1 SS_2 SS_3 Ti_1 Ti_2 Ti_3

220 specimens that exceeded the -0.20-V limit. The three speci- mens were from three groups with black bars with values between -0.20 and -0.30 V, indicating that corrosion activity was uncertain. Current Data The integrated macrocell charge is calculated based on Equation E.1: 2 (E.1)1 1 1TC TC t t i ij j j j j j( ) ( )[ ]= + − × +− − − where TC = total corrosion (C); tj = time (s) at which measurement of the macrocell is carried out; and ij = macrocell current (A) at time tj. Table E.2 shows the electrical current measured across the 100-W resistor installed between the top and bottom rebars. As expected, the negative values shown in Table E.2 indicate that the top rebar is the anode and bottom rebar is the cathode. The total integrated charge, which is used to determine the end of testing, can be calculated using the current measure- ments and Equation E.1. If the charge is greater than 150 C, the test is terminated (ASTM G109 2007a). The results were plotted in Figure E.17, which shows the variation of total charge with time. All values are below 150 C. The current data indicated one specimen in three groups (black bar and both electrochemical treatments with black bars) showed an increase in current. This finding is similar to the potential data showing uncertain corrosion activity in the same three specimens. These specimens were selected for removal of the rebar for visual inspection along with control specimens with stainless steel and titanium (BB3, ECL1, ECH3, SS1, and Ti1), as shown in Figure E.18. BB3 showed an approximately 0.75-in. length of corrosion product (see Figure E.19b). The final integrated charge was 35 C, and the lowest corrosion potential was -270 mV. The maximum macrocell current measured was 11.4 µA. ECL1 showed an approximately 1-in. length of corrosion product (see Figure E.20b). The final integrated charge was 70 C, and the lowest corrosion potential was -300 mV. The maximum macrocell current measured was 11.8 µA. ECH3 showed an approximately 0.25-in. length of corro- sion product (see Figure E.21b). The final integrated charge was 10 C, and the lowest corrosion potential was -220 mV. The maximum macrocell current measured was 3.8 µA. As shown in Figure E.22, SS1 did not show any signs of corrosion. The final integrated charge was around 1 C, and the lowest corrosion potential was -150 mV. The maximum macrocell current measured was nearly 0.2 µA. As shown in Figure E.23, Ti1 did not show any signs of cor- rosion. The final integrated charge was around 1 C, and lowest corrosion potential was -250 mV. The maximum macrocell current measured was 0.035 µA. Conclusions During the time available for this project, only one specimen from a set of three with black bars and electrochemically treated black bars showed an increase in current or potential values indicative of uncertain corrosion activity. The top bars in these specimens and in additional specimens with stainless steel and titanium reinforcements were removed for visual observation. The stainless steel and titanium bars did not exhibit corro- sion within the available time period. To discern differences between black bars and electro- chemically treated black bars, a longer test period is needed. Thus, initial observations indicate that electrochemically treated black bars may not provide the protection expected of stainless steel or titanium; however, whether they provide benefits over black bars without treatment cannot be con- cluded from this study due to time constraints. To draw firm conclusions, additional research and extended testing peri- ods are needed.

221 Table E.2. Measured Electrical Current Time BB1 BB2 BB3 ECL1 ECL2 ECL3 ECH1 ECH2 ECH3 SS1 SS2 SS3 Ti1 Ti2 Ti3 Day µA µA µA µA µA µA µA µA µA µA µA µA µA µA µA 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 50 -0.07 -0.06 -0.065 -0.06 -0.02 -0.055 -0.05 -0.025 -0.05 -0.035 -0.02 -0.025 -0.01 -0.015 -0.02 302 -0.095 -0.09 -0.1 -0.08 -0.07 -0.075 -0.045 -0.04 -0.04 -0.04 -0.045 -0.045 -0.04 -0.045 -0.04 308 -0.13 -0.09 -0.09 -0.08 -0.055 -0.07 -0.04 -0.045 -0.035 -0.02 -0.02 -0.04 -0.04 -0.03 -0.035 312 -0.12 -0.08 -0.08 -0.07 -0.07 -0.065 -0.04 -0.04 -0.035 -0.05 -0.065 -0.045 -0.04 -0.04 -0.035 336 -0.055 -0.05 -0.04 -0.055 -0.035 -0.045 -0.025 -0.02 -0.02 -0.015 -0.015 -0.02 -0.025 -0.035 -0.03 340 -0.05 -0.05 -0.04 -3.6 -0.035 -0.04 -0.03 -0.025 -0.025 -0.015 -0.01 -0.02 -0.03 -0.03 -0.03 344 -0.06 -0.05 -0.055 -8.7 -0.045 -0.05 -0.035 -0.025 -0.02 -0.045 -0.025 -0.025 -0.04 -0.04 -0.03 350 -0.06 -0.06 -0.06 -10.6 -0.04 -0.05 -0.02 -0.035 -0.02 -0.02 -0.015 -0.02 -0.025 -0.035 -0.03 354 -0.06 -0.05 -0.055 -11.5 -0.06 -0.05 -0.025 -0.02 -0.03 -0.025 -0.02 -0.02 -0.025 -0.06 -0.03 358 -0.1 -0.1 -0.08 -11.8 -0.06 -0.065 -0.03 -0.035 -0.03 -0.03 -0.03 -0.02 -0.03 -0.07 -0.025 375 -0.1 -0.1 -0.08 -10.3 -0.06 -0.065 -0.03 -0.035 -0.03 -0.03 -0.03 -0.02 -0.03 -0.07 -0.025 403 -0.6 -0.6 -11.4 -7.5 -0.3 -0.2 -0.2 -0.2 -2.2 -0.6 -0.1 -0.1 -0.1 -0.2 -0.3 424 -0.8 -0.1 -8.3 -5.4 -0.3 -0.3 -0.3 -0.2 -3.8 -0.18 -0.28 -0.34 -0.35 -0.37 -0.4

222 (a) (b) Figure E.19. BB3 specimen: (a) overall view and (b) close-up of rebar. (a) (b) Figure E.18. (a) Specimens selected for rebar removal and (b) guide line for saw cut. 0 10 20 30 40 50 60 70 80 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 Time (weeks) Integrated Charge BB_1 BB_2 BB_3 ECL_1 ECL_2 ECL_3 ECH_1 ECH_2 ECH_3 SS_1 SS_2 SS_3 Ti_1 Ti_2 Ti_3 Figure E.17. Integrated macrocell charge for all 15 specimens.

223 (a) (b) Figure E.21. ECH3 specimen: (a) overall view and (b) close-up of rebar. (a) (b) Figure E.22. SS1 specimen: (a) overall view and (b) close-up of rebar. (a) (b) Figure E.20. ECL1 specimen: (a) overall view and (b) close-up of rebar.

224 (a) (b) Figure E.23. Ti1 specimen: (a) overall view and (b) close-up of rebar.