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

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225 A p p e n d i x F Background Cathodic protection has been used in several areas, including marine and underground structures, storage tanks, and pipe- lines to protect steel from corrosion (Virmani and Clemeña 1998). Cathodic protection was not used in steel-reinforced concrete structures until applied to a bridge deck in 1973 (Stratfall 1974). The two main types of cathodic protection are impressed current cathodic protection (ICCP) and sacri- ficial galvanic protection. Most systems installed to date have been of the ICCP type. ICCP requires a power source and an anode material that enables the required current to flow between the installed generally inert anode and the steel cathode. Although ICCP systems are theoretically very good, many systems across the United States have failed and are no longer in service. In numerous cases, failure was due to a lack of dedicated maintenance and monitoring of the electrical systems and components or because the systems had been damaged by normal structure maintenance operations. In the galvanic system, the anode sacrifices itself and provides protection for the reinforcement. Galvanic systems do not require the same level of maintenance and monitoring as ICCP systems. They are practical, easy to install, and can be used in both new construction and repair; however, they have a limited life span. Concrete patch repairs are very common in reinforced con- crete structures. Often these concrete structures are chloride contaminated beyond the location of patch repairs, leading to accelerated corrosion around the patch. This phenomenon is referred to as ring anode corrosion, or the halo effect. Ring anode corrosion can be eliminated by including gal- vanic anodes within the repair. The galvanic anode corrodes instead of the reinforcing steel. This type of application now has a 10-year successful history (Sergi et al. 2008). The knowl- edge gained from this application has led to the development of higher-output galvanic anodes. Initial testing of such anodes has shown improved performance and an ability to globally protect the reinforcing steel. Known galvanic cathodic protection systems use activated anodic metals such as zinc. Activation of the metal can be achieved by exposure to chlorides when the anode is in contact with seawater (e.g., zinc jackets around reinforced concrete columns in seawater) or by embedment in a highly alkaline mortar. In the latter case, anodes are discrete “point” anodes, or units embedded in the concrete in proximity to the steel reinforcement. Depending on the service requirements, corrosion protec- tion can be divided into three distinct levels: corrosion pre- vention, corrosion control, and cathodic protection (Vector Corrosion Technologies 2013): • Corrosion prevention—Corrosion prevention is used to prevent corrosion from initiating in contaminated con- crete. If concrete repair projects are completed in accor- dance with industry guidelines (International Concrete Repair Institute), the replacement of damaged concrete will address the areas with the highest level of corrosion activity. However, after the repairs are complete, new cor- rosion sites are likely to form in the remaining contami- nated concrete. Research in the area of corrosion prevention indicates that a low applied current density (in the order of 0.4 mA/m2 of steel surface area) is effective in preventing the initiation of corrosion in concrete with significant chloride concentrations. The required current will decrease over time as chemical reactions increase the alkalinity and decrease the concentration of chloride ions around the reinforcing steel. • Corrosion control—Corrosion control systems are used when corrosion has initiated but has not yet progressed to the point of causing concrete damage. The use of corrosion control systems will provide a significant reduction in the corrosion rate and an increased service life of the New Galvanic Systems to Achieve Long-Term Cathodic Protection

226 rehabilitated structure. In many cases, this level of protec- tion can be provided with low incremental cost, as the pro- tection can be targeted at specific areas of contamination or corrosion activity. The current requirements for corro- sion control are higher than for corrosion prevention, generally in the range of 1 to 7 mA/m2. Similar to corrosion prevention, the current density required to provide cor- rosion control decreases over time as the beneficial effects of chemical reactions build up the alkalinity and decrease chloride concentrations around the reinforcing steel. • Cathodic protection—Cathodic protection provides the high- est level of protection and is intended to address ongoing corrosion activity. Cathodic protection should be selected when the highest level of protection is necessary and the cost is economically justified. Current industry standards for cathodic protection are based on 100-mV depolarization acceptance criteria. This level of protection generally requires an initial operating current between 5 and 20 mA/m2. Cur- rent may be provided by galvanic anodes or by an impressed current power supply. Historically, galvanic anodes provided a level of current output per unit that was sometimes too low to achieve the desired level of protection. The development of improved anode units that can produce a higher level of current by increasing the driving voltage between the anode and steel reinforcement has improved performance and allowed gal- vanic anodes to meet the full range of desirable corrosion protection levels. The advantages of these types of galvanic systems over ICCP are the self-regulating current output of the system and the much-reduced requirement of monitor- ing and maintenance. Some recent initial work has enabled increased perfor- mance of galvanic anodes by modifying the surface area of the metal by design and increasing the driving voltage of the anode unit. Figure F.1 shows the increase in cumula- tive charge with time of anodes with increasing metal sur- face area. It is also possible to increase the current density output by using high-voltage anodes, as shown in Figure F.2. Problem Statement Galvanic systems can delay the onset of corrosion and reduce the rate of corrosion of the reinforcing steel in reinforced struc- tures. Furthermore, the degree of protection achieved and the extension in the service life of the reinforced concrete bridge elements can be extended by improving the performance of galvanic systems. Description of the Concept Galvanic systems make use of a sacrificial metal, such as zinc, which is naturally anodic when coupled to steel and corrodes preferentially to the steel cathode, giving up electrons to pro- tect the steel (Virmani and Clemeña 1998). Objectives of the Research The objective of this research was to evaluate different promis- ing concepts associated with the new galvanic systems in order to delay the onset of corrosion and to reduce the rate of corro- sion of the reinforcing steel. The galvanic systems evaluated had an ordinary anode, an anode with a larger surface (four times more zinc than ordinary anodes), and two levels of high-voltage anode. Before the initiation of the laboratory evaluation of the anodes, a comprehensive literature survey was conducted. 0 50 100 150 200 250 300 350 0 5 10 15 20 25 Cu m ul at iv e ch ar ge Time (days) Standard surface area Surface area x 2 Surface area x 4 Figure F.1. Cumulative charge with time of anodes with different metal surface areas.

227 Research Approach Introduction Cathodic protection is used to extend the service life of rein- forced concrete structures, generally existing structures, which are chloride contaminated and are exhibiting corrosion. The intent of this research was not to test specific products, but rather to evaluate the ability of galvanic anodes in gen- eral to provide corrosion prevention or cathodic protection. Because available galvanic anodes offer limited protection, the ability to improve the level of protection of anodes with more surface area or with higher voltage output was investi- gated. Currently, proprietary systems exist for more surface area and for high-voltage output; these systems were evalu- ated to determine the extent of protection in highly chloride- contaminated concrete. Anode-embedding mortar and its effects on current output were not addressed in this research, but should be pursued in future studies. Organization and Conduct of the Research Small-scale laboratory testing was conducted to evaluate the potential of using galvanic anodes to extend the service life of reinforced concrete structures and the level of protection provided by different anode systems (increased metal surface, higher-voltage output). Data collection included the measure- ment of the current, current density, potentials, and polariza- tion versus time. The following tasks were accomplished to meet the research objectives: Task 1. Summarize the literature of cathodic protection, includ- ing galvanic systems. Task 2. Obtain material and equipment to be used during the testing stage. Task 3. Fabricate samples using different galvanic systems. Task 4. Set up automated monitoring system to collect long- term data. Task 5. Analyze the collected data and destructively analyze anodes and steel bars. Task 6. Prepare the final report and provide recommendations based on the results. Analysis of Available data A Federal Highway Administration (FHWA) report states, “The only rehabilitation technique that has proven to stop corrosion in salt-contaminated bridge decks regardless of the chloride content of the concrete is cathodic protection” (R. A. Barnhart, memorandum, FHWA Position on Cathodic Pro- tection, 1982). An advantage of using cathodic protection as a repair method for reinforced concrete bridges is that only spalls and delaminated concrete need to be repaired. Chloride- contaminated concrete that is still sound can remain in place because the cathodic protection system will reduce the con- centration of chloride ions adjacent to the protected reinforc- ing bars, preventing further corrosion. This can significantly reduce repair costs (Polder 1998). There are three basics components to a cathodic corrosion protection system (Durham and Durham 2005): • An anode that supplies current in a corrosion circuit; • A cathode that receives current in a corrosion circuit; and • An electrolyte that is a nonmetallic medium, with some moisture content, which supports the flow of ionic current. 0 5 10 15 20 25 Enhanced Voltage Anode Standard Anode M ea n cu rr en t d en sit y, st ee l ( m ²A ) Figure F.2. Mean current density over 2 months for anodes with enhanced voltage output.

228 The current for cathodic protection can be supplied to a bridge deck by one of two methods: (1) an external power source (impressed current) or (2) an anode that is made from a material that is more active and corrodes preferentially to the reinforcing steel (sacrificial anode). Refer to Figure F.3 for schematics of these two cathodic protection systems. Both impressed current and sacrificial galvanic systems have been used successfully on bridges in the United States. Each method has specific characteristics that make it more effective than the other in a given situation. Table F.1 lists some of the general characteristics of each method. Impressed current sys- tems are used most often on bridge decks. Some impressed current anodes can also be used on bridge substructure mem- bers. The use of galvanic anodes has historically been limited to substructure members (Kepler et al. 2000); however, deck applications have become much more common in recent years. Table F.2 lists some estimated current density requirements for cathodic protection in various material and environmen- tal conditions (Kepler et al. 2000). The following conclusions are based on a review of studies reporting the performance of various cathodic protection systems (Kepler et al. 2000): • Cathodic protection can effectively stop corrosion in con- taminated reinforced concrete structures and reduce the concentration of chloride ions at the steel surface of pro- tected reinforcement. • The most common impressed-current anode in use for cathodic protection of reinforced concrete bridge decks is the titanium mesh anode, used in conjunction with a con- crete overlay. • Zinc mesh pile jacket anodes show promise as sacrificial anodes for the splash zone of bridge piles in a marine envi- ronment. Zinc–hydrogel anodes can provide protection for substructure members in marine or inland environments, as long as water can be kept out of the system. Activated zinc anode strips can be embedded in concrete jackets and over- lays to provide distributed corrosion protection. • Cathodic protection can be applied effectively and safely to prestressed concrete bridge members. However, if the resis- tivity of the concrete is not uniform, it may be difficult to obtain sufficient protection at locations where resistivity is high without generating hydrogen in areas of low resistance. Cathodic protection is not recommended for prestressed concrete structures with very diverse resistivity, which is often caused by large variations in moisture content. • When applying cathodic protection to prestressed concrete, the voltage should be kept low enough that the potential required for hydrogen generation at the surface of the pre- stressing steel is not reached. +- 4e Negative Return DC Power Supply Anode Cable (Insulated) Anode Sea Water Protected Structure 4Cl 2Cl2 O2+2H2O 4OH (a) Anode Cable Aluminum Anode Sea Water Protected Structure 3O2+6H2O 12e- 12OH- 4Al+++ (b) Figure F.3. Scheme of cathodic protection systems: (a) impressed current and (b) sacrificial anode. Table F.1. Comparison of Characteristics of Cathodic Protection Impressed Current Sacrificial Anode External power required Requires no external power Driving voltage can be varied Fixed driving voltage Current can be varied Limited current Can be designed for almost any current requirement Usually used where current requirements are small Can be used in any level of resistivity Usually used in low-resistivity electrolytes

229 Impressed current systems can be costly and may require significant maintenance and monitoring. Galvanic systems may be easier to use; however, they provide a limited service life and level of corrosion protection. In repairs, sacrificial galvanic anodes are considered for localized corrosion pro- tection because they are simple and easy to apply. experimental program Testing Facility All test specimens were prepared at the University of Nebraska–Lincoln in the civil engineering laboratory. Construction Overview The ability of embedded galvanic anodes to provide sufficient output to cathodically protect the reinforcing steel from fur- ther corrosion was determined using slabs. Different anodes with varying output and levels of protection were studied. The specimens measured 18- × 18-in. and were 8 in. thick to simulate a portion of a bridge deck. The test matrix included conventional reinforcing steel and galvanic anodes with differ- ent surface areas or voltage outputs. Test Setup The concrete slabs were cast in two layers. The bottom layer had uncontaminated concrete, and the top layer had concrete con- taminated with salt. Figure F.4 shows the galvanic system test specimen. Five variables were evaluated: • Black bar embedded in concrete without anode as a con- trol specimen (BB); • Black bar embedded in concrete with ordinary anode (OA); • Black bar embedded in concrete with a larger anode having a surface area four times the ordinary (OA4); • Black bar embedded in concrete with a high-voltage anode (under development) at Level 1; this provided higher applied voltage than a standard galvanic anode (HVAL); and • Black bar embedded in concrete with a high-voltage anode (under development) at Level 2; this provided a higher volt- age than Level 1 (HVAH). Three specimens of each variable were prepared. The dimen- sions of the specimens are given in Figure F.5. The thickness of the slab was 8 in. Material The following materials were used to evaluate the new gal- vanic systems: • Concrete 44 Concrete (1 yd3) with proportions given in the specimen preparation below was delivered by the local ready-mixed concrete plant. Table F.2. Practical Cathodic Protection Current Density Requirements for Varying Environments Environment Surrounding Steel Reinforcement Current Density (mA per m2 of reinforcement) Alkaline, no corrosion occurring, low oxygen resupplya 0.1 Alkaline, no corrosion occurring, exposed structurea 1–3 Alkaline, chloride present, dry, good-quality concrete, high cover, light corrosion observed on reinforcement 3–7 Chloride present, wet, poor-quality concrete, medium-low cover, widespread pitting and general corrosion on steel 8–20 High chloride levels, wet fluctuating environment, high oxygen level, hot, severe corrosion on steel, low cover 30–50 a This is typical of a corrosion prevention (cathodic prevention) application as described in BS EN ISO 12696:2012, Cathodic Protection of Steel in Concrete (BSI 2012). The current requirement for cathodic prevention (corrosion prevention) in the standard is stated as 0.2–2 mA/m2. Figure F.4. Three-dimensional view of new galvanic system test specimen.

230 44 Half of the volume (0.5 yd3) was used to cast the bottom 4-in. layer. After approximately 5 days of curing, the remaining 4-in. upper layer was cast using concrete with a 10-lb/yd3 admixed chloride. • Steel reinforcement consisted of 120 mild steel rebars (eight black bars per specimen), Grade 60, 0.5 in. in diam- eter (No. 4), and 22 in. long (see Figure F.6). • Stainless steel screws and nuts 44 120 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 44 240 Stainless steel nuts (two per bar) to fit the screws. • Two-part waterproof epoxy; this epoxy met the chemical resistance requirement by ASTM C881 for a Type IV, Grade 3, Class E specification epoxy (ASTM C881 2010). • Heat-shrink tube with internal adhesive (see Figure F.7). • Sodium chloride. • Epoxy sealer to cover the sides and top surface outside the dam. Type III, Grade 1, Class C epoxy sealer was used in accordance with ASTM specifications (ASTM C881 2010). • Plastic dams measuring 13 in. wide and 13 in. long with a minimum height of 3 in. and a wall thickness of ±¹⁄8 in. for placement on the test specimen. • Silicone caulk for sealing the outside of the plastic dam on top of the concrete. (a) (b) Figure F.5. Dimensions of test specimen: (a) side view and (b) top view; dam on top is shown in light green. Figure F.6. Mild steel reinforcement with a length of 22 in. Figure F.7. Heat-shrink tube.

231 • Six sacrificial anodes of each type (i.e., ordinary anodes, anodes with a larger surface [four times more zinc than ordinary anodes], and two levels of high-voltage anode) for a total of 24 (see Figure F.8). Anodes were connected to the junction box by wire. • Reference electrodes 44 Surface electrodes (e.g., silver–silver chloride electrodes); and 44 30 Embeddable reference electrodes (see Figure F.9), such as silver–silver chloride electrodes, for measuring the corrosion potential and for long-term monitoring. • Multimeter. • Automated data acquisition system to record all the voltage and current outputs. (a) (b) (c) (d) Figure F.8. Four types of anode were used: (a) ordinary anodes (OA), (b) anodes with four times more zinc than an ordinary anode (OA4), and high-voltage anodes with (c) low output (HVAL) and (d) high output (HVAH). Figure F.9. Embeddable reference electrode.

232 Specimen Preparation The concrete slabs were prepared similar to the ones described in ASTM G109 (ASTM G109 2007a). The rebars were cleaned by sandblasting to a near white metal finish, soaked in hexane, and air dried as shown in Figure F.10. 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. piece of heat-shrink tubing was placed so that 13 in. of bar were kept bare inside the slab. The rebar lengths protruding from the form were coated with two-part epoxy. Figure F.11 shows the applica- tion of heat-shrink tubing and epoxy coating. Wooden forms measuring 18 × 18 × 8 in. were fabricated and brushed with oil as shown in Figure F.12 for easy form removal. The rebar was placed so that approximately 2 in. projected from the form, as shown in Figure F.13. The minimum con- crete cover over bars was 1 in. Figure F.10. Mild reinforcement before and after sandblasting. (a) (b) Figure F.11. (a) Application of heat-shrink tubing and (b) rebars after epoxy coating of ends. The concrete was made in accordance with ASTM C192 (ASTM C192 2007b) and had a water–cement ratio equal to 0.5, a cement content of 600 lb/yd3, an air content of 5%, and a minimum slump of 2 in. The first 4-in. layer was cast with conventional concrete (no salt admixed). A plastic sheet was used to keep the moisture in the concrete until the placement of the upper second layer, as shown in Figure F.14b. Before placing the second layer, two anodes were placed close to each other in the center of the mold on top of the bottom layer. In addition, two embeddable reference elec- trodes were fixed at two locations, as shown in Figure F.15. The top 4 in. of concrete was placed with concrete admixed with chloride (10 lb/yd3). Concrete was consolidated by rod- ding and finished by a wood float, as shown in Figure F.16. Wet burlap and plastic sheet were used for curing. Forms were removed 4 days after casting, although the burlap and plastic sheet were kept until 28 days. After 28 days of curing, the plastic dam was placed on top, as shown in Figure F.17. All four vertical sides and the top surface outside the plastic dam were sealed with an epoxy sealer. Wires were attached to the junction box. Testing Procedure The testing procedure for the determination of corrosion activity involved measuring 1. Half-cell potentials (ASTM C876 2009) at nine locations on the specimen; 2. Current flowing from the anode to each pair (a total of four pairs, two on top and two at the bottom of the speci- men) of rebars hourly; at the same time, the corrosion potential was measured by the embedded electrodes; and

233 (a) (b) Figure F.12. (a) Wooden forms before and (b) after application of oil. (a) (b) Figure F.13. (a) Forms ready for placement of concrete and (b) specimen close-up (bottom layer). (a) (b) Figure F.14. (a) Specimens after placement of bottom layer and (b) plastic sheet to prevent moisture loss.

234 (a) (b) Figure F.15. Installation of (a) embeddable electrode and (b) OA4 anode. (a) (b) Figure F.16. (a) Casting of the second layer of concrete and (b) specimens after wood-float finishing. Figure F.17. Specimens ready to start the wet–dry cycle. 3. Current flowing during depolarization when the anode was disconnected; at the same time, the corrosion poten- tial were measured by both the embedded electrodes and the half-cell system. A second data logger with quick read- ing capability (10 reads per second) was used during the procedure to capture the exact moment when the anode was turned off and on. The following steps were used in the testing procedure: Step 1. Seven days after casting, before connecting the anode to the rebars for the first time, the corrosion potential was measured to establish the baseline level of corrosion potential of the steel. A half-cell system with a silver– silver chloride electrode was used to measure the corro- sion potential. The tip of the reference electrode was positioned on a small wet pad to stabilize the readings,

235 as shown in Figure F.18. The same procedure was repeated three times during each wet–dry cycle. The corro- sion potential was measured before ponding with the water, after removal of the water, and at the middle of the dry cycle. Step 2. Immediately after the first potential map, the first anode was connected to the steel. The current delivered by the anode was measured, after which the anode was immedi- ately disconnected. The second anode was then connected to the steel, and the current was measured. If both anodes were active (i.e., produced currents of the order of milliamperes), one of them was chosen and permanently connected to the steel. The other anode remained redundant until the end of the experiment. If one anode appeared faulty (e.g., the elec- trical connection was problematic), the spare anode would be used. Step 3. The specimens were ponded with water (no salt) for 4 days. Approximately 2 L water (around 10-mm height) were added to the reservoir. At the end of the wet period, water was removed by vacuum, as shown in Figure F.19. Step 4. The data logger (see Figure F.20) was used to take read- ings every hour. The automated acquisition system recorded the total current measurements. Step 5. For the depolarization measurements at approximately every 10 weeks, a potential map was determined while the anode and steel bars were connected. The anode was then disconnected (using the switch). Step 6. Four hours later, a new potential map was determined. The difference between the instant-off potential and the 4-h depolarization potential were used to determine the parameter Depol4. Step 7. Twenty-four hours after disconnection, another potential map was determined. The difference between the instant-off potential and this 24-hour depolarization potential was used to determine the parameter Depol24. After the conclusion of the depolarization test, the anode was reconnected to all steel bars. The anode was kept con- nected to all the rebars via the junction box until the next depolarization test. The test specimens are shown in Figure F.21. Test Results This section summarizes the data collected from • The half-cell potential system; • The current flowing from the anodes to each pair of rebars and the corrosion potential at the location of two embed- ded electrodes in each specimen; and Figure F.18. Measuring the half-cell potential. Figure F.19. Vacuuming off the water at the end of the wet period. Figure F.20. Laptop and data logger system used to collect the data.

236 • The current flowing during the instant-off and -on proce- dure from the anodes to each pair of rebars and the corro- sion potential at the location of two embedded electrodes. The experimental program started with the first half-cell potential measurement taken on September 23, 2010 (Day 0). After establishing the baseline readings, all samples were sub- jected to cycles of 4 days wet and 10 days dry. In addition to the half-cell readings taken at the end of each dry cycle, two extra sets of readings were taken to better evaluate and observe the specimens during the wet–dry cycles. Each specimen was identified using the labels given in Table F.3. Five variables were tested; three specimens for each variable were made (for a total of 15 specimens) to provide statistical significance. Although two anodes were installed in each specimen, only one was used in the tests. The output voltage of each anode was measured separately. The anode with the higher potential reading measured was selected and was connected perma- nently with the rebars throughout the experiment. Table F.4 shows the potential reading from each anode measured by a multimeter. The shaded values refer to the chosen anodes. Half-Cell Potential Data Figure F.22 shows the half-cell potential readings for all speci- mens. This plot represents the average values of corrosion potential measured at nine distinct points on each slab. The measurement was conducted three times during each wet– dry cycle. Initially all specimens had similar corrosion potential val- ues. The control specimens (BB), with no anode, had the lowest negative corrosion potential values; these values were steady throughout the experiment. All specimens with anodes Figure F.21. Test specimens. Table F.3. Sample Labels Label Type of Anode BB_1 BB_2 BB_3 None None None OA_1 OA_2 OA_3 Ordinary anode Ordinary anode Ordinary anode OA4_1 OA4_2 OA4_3 Anode with four times the surface area of the ordinary anode Anode with four times the surface area of the ordinary anode Anode with four times the surface area of the ordinary anode HVAL_1 HVAL_2 HVAL_3 High-voltage anode: low level High-voltage anode: low level High-voltage anode: low level HVAH_1 HVAH_2 HVAH_3 High-voltage anode: high level High-voltage anode: high level High-voltage anode: high level Table F.4. Initial Voltage Output Label Anode 1 Anode 2 OA_1 0.925 V 0.927 V OA_2 OA_3 0.971 V 0.927 V 0.961 V 0.923 V OA4_1 0.852 V 0.832 V OA4_2 OA4_3 0.845 V 0.888 V 0.853 V 0.894 V HVAL_1 HVAL_2 HVAL_3 1.864 V 0.815 V 1.714 V 0.837 V 0.778 V 1.463 V HVAH_1 HVAH_2 HVAH_3 2.245 v 3.270 v 3.320 v 1.817 V 2.555 V 1.767 V had their corrosion potential shift in the negative direction after the anode was connected to the rebars. The OA, OA4, and HVAL specimens had steady potential readings. Two HVAH specimens produced variable results that may have been due to variation in the production of the prototypes. The highest negative corrosion potentials were provided by the HVAH specimens, followed by the HVAL and OA4 specimens, then by OA, and finally by the BB speci- mens. Higher negative corrosion potentials indicate that more corrosion protection was being provided. Current Flow and Corrosion Potential Data were collected hourly by the data-logger system. Seven outputs were collected for each specimen. Table F.5 shows the

237 labels used to identify each one of these outputs, and Figure F.23 shows the location of each monitored element on the sample. Two data analyses were conducted. The first series of data presented the electrical current flowing from the anode to all four pairs of rebars. The second data series presented the corrosion potential measured by the embedded electrodes at two locations. ElEctrical currEnt Data analysis This subsection presents the measurement of electrical current flowing from the anode to the four pairs of rebars. The data logger recorded the voltage (electrical potential) hourly across the resistors. The electrical current was calculated by dividing the voltage by the resistance; that is, i = V/R, where i is the cur- rent in milliamperes, V is the voltage in millivolts, and R is a 10-ohm resistor. Figure F.24 through Figure F.27 show the data collected over 56 weeks. The plots show the variation of electrical cur- rent in milliamperes with time in weeks. For the control specimens (BB), since no anode was installed, there is no current plot. Figure F.24 shows the results for the OA specimens. The ordinary anodes contained the least amount of zinc among all anodes tested. The initial current provided by this anode was 0.5 to 0.7 mA. The final current value decreased to a range of 0.1 to 0.3 mA. Figure F.25 shows the results for OA4 specimens. The OA4 anode had four times the surface area as the ordinary anode. The initial current provide by this anode was 1.0 to 1.4 mA. The final current value decreased to a range of 0.4 to 0.6 mA. Figure F.26 shows the results for HVAL specimens. The high-voltage anode (HVAL) contained the same amount of zinc as the ordinary anode, but the voltage of the anode was enhanced. The initial current provided by this anode was 0.6 to 1.4 mA. The final current value decreased to around 0.4 mA. The current results were very similar to the OA4 anode results. 800 700 600 500 400 300 200 100 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 nti al (m V) Time (weeks) Average values of Half cell potential BB_1 BB_2 BB_3 OA_1 OA_2 OA_3 OA4_1 OA4_2 OA4_3 HVAL_1 HVAL_2 HVAL_3 HVAH_1 HVAH_2 HVAH_3 Figure F.22. Half-cell potential for all 15 specimens. Table F.5. Description of Identifying Labels Label Description TopL TopT BotT BotL Anode EMid ECor Two longitudinal rebars at top layer Two transverse rebars at top layer Two transverse rebars at bottom layer Two longitudinal rebars at bottom layer Anode Embedded electrode at middle of reinforcement Embedded electrode at corner of reinforcement Figure F.23. Identification of monitored elements.

238 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 Cu rr en t( m A) Time (weeks) Ordinary anode OA_1 OA_2 OA_3 Figure F.24. Electrical current variation for specimens with OA anodes. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 Cu rr en t( m A) Time (weeks) Anode with 4x amount of zinc OA4_1 OA4_2 OA4_3 Figure F.25. Electrical current variation for specimens with OA4 anodes.

239 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 Cu rr en t( m A) Time (weeks) High voltage anode (level 1) HVAL_1 HVAL_2 HVAL_3 Figure F.26. Electrical current variation for specimens with HVAL anodes. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 Cu rr en t( m A) Time (weeks) High voltage anode (level 2) HVAH_1 HVAH_2 HVAH_3 Figure F.27. Electrical current variation for specimens with HVAH anodes.

240 1000 900 800 700 600 500 400 300 200 100 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 nt ia l( m V) Time (weeks) Noanode (control) BB_1 (Emid) BB_1 (Ecor) BB_2 (Emid) BB (surface) Figure F.28. Corrosion potential data for control specimens (BB). Figure F.27 shows the results for HVAH specimens. The high- voltage anode (HVAH) contained the same amount of zinc as the ordinary anode, but the voltage of the anode was increased to be greater than the HVAL anodes. The initial current pro- vided by this anode was 3.0 to 4.2 mA. The final current decreased to a range of 0.2 to 0.3 mA. During the early stage of the testing, a sudden drop in the current occurred for both HVAH_1 and HVAH_3. The spare anode was connected, and the testing continued. corrosion PotEntial Data This subsection presents the corrosion potential data col- lected at the two locations of the embedded reference elec- trodes identified in Table F.5. The data logger recorded the potential of the reinforcing steel relative to the embedded reference electrodes on an hourly basis. Although all embed- ded electrodes were tested individually during the installa- tion, some of them exhibited abrupt changes of corrosion potential measurements during the test. It was believed that these unexpected changes were caused by malfunctioning electrodes that could not be detected during the preliminary tests. Regard less of the malfunctioning of some embedded electrodes, the results clearly indicated the difference in behavior of various anode types. Figure F.28 through Figure F.32 show the data collected over 56 weeks. The plots show the variation in corrosion potential (in millivolts) with time (days) for all 15 specimens. The data from the malfunctioning embedded electrodes were removed from the plot. Figure F.28 shows the results for BB specimens. No anode was installed in the specimens, and consequently no great variation of corrosion potential was observed. The electrical potential measured by the embedded electrodes was around -250 mV, which decreased to values of -100 mV at the end of testing. Very good agreement was found between the embed- ded electrode values and the surface potential values. Figure F.29 shows the results for the OA specimens. The elec- trical potential measured by the embedded electrodes ranged from -400 to -300 mV; these values decreased to around -300 to -150 mV at the end of testing. The average values of the corrosion potential measured at the top surface of each test specimen showed good agreement with the potential values from the embedded electrodes. Figure F.30 shows the results for OA4 specimens. The electri- cal potential measured by the embedded electrodes was around -500 mV, which decreased to a range of -350 to -500 mV at the end of testing. Again, good agreement was observed between the average corrosion potential measured at the top surface of each test specimen and that obtained from the embedded electrodes. Figure F.31 shows the results for HVAL specimens. The electrical potential measured by the embedded electrodes was around -450 mV; this value was largely maintained at the end of testing. The potential values measured at the top surface of each test specimen showed similar behavior. Figure F.32 shows the results for specimens with the HVAH anodes. Unlike the other anodes, the HVAH specimens showed greater variation of the corrosion potential measurements. The electrical potential measured by the embedded electrodes ranged from -650 to -800 mV, which decreased to a range of -100 to -400 mV at the end of testing. Aside from the larger variability of the measurements, the potential measured at the surface of all three specimens followed the same trend and magnitudes of the values measured inside the concrete.

241 1000 900 800 700 600 500 400 300 200 100 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 nti al (m V) Time (weeks) Anode with 4x amount of zinc OA4_1 (Emid) OA4_1 (Ecor) OA4_2 (Emid) OA4_2 (Ecor) OA4_3 (Ecor) OA4 (surface) Figure F.30. Corrosion potential data for specimens with OA4 anodes. 1000 900 800 700 600 500 400 300 200 100 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 nti al (m V) Time (weeks) Ordinary anode OA_1 (Emid) OA_2 (Ecor) OA_3 (Emid) OA_3 (Ecor) OA (surface) Figure F.29. Corrosion potential data for specimens with OA anodes.

242 1000 900 800 700 600 500 400 300 200 100 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 nti al (m V) Time (weeks) High voltage anode (level 1) HVAL_1 (Ecor) HVAL_2 (Emid) HVAL_2 (Ecor) HVAL_3 (Ecor) HVAL (surface) Figure F.31. Corrosion potential varying with time for specimens with HVAL anodes. 1000 900 800 700 600 500 400 300 200 100 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 nt ia l( m V) Time (weeks) High voltage anode (level 2) HVAH_1 (Emid) HVAH_1 (Ecor) HVAH_3 (Emid) HVAH_3 (Ecor) HVAH (surface) Figure F.32. Corrosion potential data for specimens with HVAH anodes.

243 Depolarization Testing Corrosion rates were estimated through a depolarization test- ing procedure. Four depolarization measurements were con- ducted at approximately 10-week intervals. The tests consisted of collecting a series of readings during the temporary dis- connection of the anodes, 4 and 24 h after disconnection, and finally during the anode reconnection (turn-on). The proce- dure started with the initial reading taken before the anodes were disconnected, and an intermediate reading was conducted 4 h after the anodes were disconnected (4 h off). Finally, 24 h after disconnection and before reconnection (turn-on) of the anodes, a final reading was taken (24 h off). The data collected during this procedure were used to esti- mate the corrosion rate by using the Butler–Volmer equation (see Equation F.1), which describes one of the most fundamen- tal relationships in electrochemistry (Bard and Faulkner 2001). The equation describes how the electrical current on an elec- trode depends on the electrode potential, considering that both a cathodic and an anodic reaction occur on the same electrode. In other words, the equation can be used to estimate the cor- rosion rate of steel reinforcement in concrete. The data collected during the 24-h depolarization test period was used to estimate the corrosion current of the reinforcing steel in each of the test specimens with anodes using a solution to the Butler–Volmer equation. = ∆ β   − − ∆ β   i i E E exp 2.3 exp 2.3 (F.1) c a corr appl where icorr = corrosion rate (mA/m2); iappl = applied electrical current (mA/m2); DE = observed corrosion potential (mV); bc = cathodic Tafel’s slope (assumed 120 mV); and ba = anodic Tafel’s slope (assumed 60 mV). Table F.6 shows typical corrosion rate values and their respec- tive level of relevance. First DEPolarization Table F.7 shows the corrosion potential measurements during a 24-h depolarization period. The presented values were cal- culated by taking the average over all nine surface points of each specimen. During the 24-h depolarization period, it was observed that control specimens did not exhibit changes to the corrosion potential; however, all the specimens with anodes showed a large shift in potential after the disconnection of the anode. The largest change was observed for the HVAH specimens, followed by HVAL and OA4 specimens, and finally by the OA specimens. In the specimens with anodes, the corrosion potential of the reinforcing steel 4 h after disconnection aver- aged -103 mV. The corrosion potentials decreased further to around -84 mV after 24 h. Figure F.33 shows the normalized values of corrosion poten- tials during the first depolarization period. Table F.8 shows the corrosion rate estimation. Although the concrete used in the specimens had a high level of salt per unit volume of concrete, the results indicated little or no corrosion. sEconD DEPolarization Table F.9 shows the variation of corrosion potentials during the second 24-h depolarization test period. The values pre- sented are the average of all nine surface corrosion potential measurements taken on each sample. Table F.7. Variation of Corrosion Potential During First Depolarization Period Sample Label Time of Measurement 0 Hour (mV) 4 Hours (mV) 24 Hours (mV) BB_1 BB_2 BB_3 -149.8 -127.3 -157.8 -153.4 -125.9 -148.1 -149.9 -123.0 -162.3 OA_1 OA_2 OA_3 -364.1 -377.6 -351.7 -116.3 -108.9 -87.9 -122.0 -88.9 -69.9 OA4_1 OA4_2 OA4_3 -496.6 -465.8 -474.6 -110.0 -106.0 -83.9 -81.9 -83.2 -62.2 HVAL_1 HVAL_2 HVAL_3 -463.0 -431.1 -463.2 -111.8 -106.4 -94.1 -85.4 -90.4 -65.1 HVAH_1 HVAH_2 HVAH_3 -568.8 -570.2 -648.1 -82.1 -92.6 -131.2 -44.4 -91.0 -127.4 Table F.6. Typical Corrosion Rate Values Measurement Corrosion Rate <0.5 µA/cm2 Negligible 0.5–5 µA/cm2 Slow 5–15 µA/cm2 Moderate >15 µA/cm2 High

244 100.00 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 0 4 8 12 16 20 24 Co rr os io n Po te nt ia l( m V) Time (hours) Normalized values of Half cell potential BB_1 BB_2 BB_3 OA_1 OA_2 OA_3 OA4_1 OA4_2 OA4_3 HVAL_1 HVAL_2 HVAL_3 HVAH_1 HVAH_2 HVAH_3 Figure F.33. Normalized values of half-cell potential during first depolarization. Table F.9. Variation of Corrosion Potential During Second Depolarization Period Sample Time of Measurement 0 Hour (mV) 4 Hours (mV) 24 Hours (mV) BB_1 BB_2 BB_3 -134.9 -94.9 -144.4 -132.4 -91.0 -136.2 -111.9 -77.0 -122.7 OA_1 OA_2 OA_3 -362.1 -354.2 -365.1 -99.7 -85.0 -82.9 -63.3 -55.6 -40.6 OA4_1 OA4_2 OA4_3 -463.2 -440.6 -452.0 -95.4 -95.0 -92.8 -53.8 -54.3 -46.4 HVAL_1 HVAL_2 HVAL_3 -447.4 -404.7 -445.6 -104.4 -87.7 -79.0 -54.6 -54.7 -45.8 HVAH_1 HVAH_2 HVAH_3 -565.6 -529.3 -631.9 -88.1 -72.6 -98.2 -9.8 -21.4 -27.1 Table F.8. Corrosion Rate Estimation Label iappl (mA/m2) DE (mV) bc (mV) ba (mV) icorr (mA/m2) Corrosion Rate (µA/cm2) Rating OA_1 OA_2 OA_3 538.02 460.28 487.00 242.11 288.67 281.78 120 120 120 60 60 60 5.19 1.82 2.20 0.52 0.18 0.22 Slow Negligible Negligible OA4_1 OA4_2 OA4_3 1110.67 941.92 968.46 414.67 382.56 412.33 120 120 120 60 60 60 0.39 0.62 0.36 0.04 0.06 0.04 Negligible Negligible Negligible HVAL_1 HVAL_2 HVAL_3 907.29 670.29 804.60 377.56 340.67 398.11 120 120 120 60 60 60 0.65 0.98 0.39 0.07 0.10 0.04 Negligible Negligible Negligible HVAH_1 HVAH_2 HVAH_3 2279.74 2072.82 2605.68 524.33 479.22 520.67 120 120 120 60 60 60 0.10 0.21 0.12 0.01 0.02 0.01 Negligible Negligible Negligible

245 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 0 4 8 12 16 20 24 Co rr os io n Po te nti al (m V) Time (hours) Normalized values of Half cell potential BB_1 BB_2 BB_3 XP_1 XP_2 XP_3 XP4_1 XP4_2 XP4_3 HVAL_1 HVAL_2 HVAL_3 HVAH_1 HVAH_2 HVAH_3 Figure F.34. Normalized values of half-cell potential during second depolarization. During the second depolarization period of 24 h, it was observed that the corrosion potential of the control speci- mens did not change; however, all the specimens with anodes showed a large shift in potential after the disconnection of the anodes. The largest change was observed for the HVAH speci- mens, followed by HVAL and OA4 specimens, and finally by the OA specimens. Despite the different initial corrosion potential of each sample, the potential of the reinforcing steel 4 h after disconnection was around -90 mV for all specimens with anodes. The corrosion potential of the reinforcing steel 24 h after disconnection averaged -44 mV. Figure F.34 shows normalized values of the corrosion poten- tial during the second depolarization period. Table F.10 shows the corrosion rate estimation. Table F.10. Corrosion Rate Estimation Label iappl (mA/m2) DE (mV) bc (mV) ba (mV) icorr (mA/m2) Corrosion Rate (µA/cm2) Rating OA_1 OA_2 OA_3 432.66 350.86 402.85 298.78 298.67 324.56 120 120 120 60 60 60 1.41 1.15 0.80 0.14 0.11 0.08 Negligible Negligible Negligible OA4_1 OA4_2 OA4_3 814.88 630.26 682.24 409.44 386.22 405.56 120 120 120 60 60 60 0.32 0.38 0.29 0.03 0.04 0.03 Negligible Negligible Negligible HVAL_1 HVAL_2 HVAL_3 714.72 441.83 634.69 392.89 350.00 399.78 120 120 120 60 60 60 0.38 0.54 0.30 0.04 0.05 0.03 Negligible Negligible Negligible HVAH_1 HVAH_2 HVAH_3 1662.79 1393.41 2467.85 555.78 507.89 604.78 120 120 120 60 60 60 0.04 0.08 0.02 0.00 0.01 0.00 Negligible Negligible Negligible

246 Table F.11. Variation of Corrosion Potential During Third Depolarization Period Sample Time of Measurement 0 Hour (mV) 4 Hours (mV) 24 Hours (mV) BB_1 BB_2 BB_3 -134.1 -64.1 -122.7 -137.6 -68.4 -127.7 -127.4 -65.7 -126.2 OA_1 OA_2 OA_3 -350.0 -342.8 -361.3 -92.1 -92.4 -85.6 -54.0 -52.4 -42.6 OA4_1 OA4_2 OA4_3 -473.0 -439.3 -448.6 -110.7 -101.1 -95.1 -67.6 -59.1 -58.9 HVAL_1 HVAL_2 HVAL_3 -454.1 -411.6 -428.3 -104.7 -95.6 -92.1 -54.2 -59.3 -56.7 HVAH_1 HVAH_2 HVAH_3 -581.4 -402.9 -367.8 -87.1 -86.8 -100.1 -24.7 -33.3 -59.7 100.00 0.00 100.00 200.00 300.00 400.00 500.00 600.00 0 4 8 12 16 20 24 Co rr os io n Po te nt ia l( m V) Time (hours) Normalized values of Half cell potential BB_1 BB_2 BB_3 XP_1 XP_2 XP_3 XP4_1 XP4_2 XP4_3 HVAL_1 HVAL_2 HVAL_3 HVAH_1 HVAH_2 HVAH_3 Figure F.35. Normalized values of half-cell potential during third depolarization. Even though the concrete used in the specimens had a high level of salt per unit volume of concrete, the results indicated no corrosion activity. thirD DEPolarization Table F.11 shows the variation of corrosion potential during the third 24-h depolarization period. The values presented were calculated by taking the average of all nine surface cor- rosion potential measurements for each sample. During the third 24-h depolarization period, it was observed that the corrosion potentials of the control specimens did not change; however, all the specimens with anodes showed a large shift in potential after the disconnection of the anodes. The largest change was observed for the HVAH specimens, followed by HVAL and OA4 specimens, and finally by the OA specimens. Despite the different initial corrosion potential of each sample, the potential of the reinforcing steel 4 h after disconnection was around -95 mV for all specimens with anodes. The corrosion potential of the reinforcing steel 24 h after disconnection averaged -52 mV. Figure F.35 shows normalized values of the corrosion poten- tial during the third depolarization period. Table F.12 shows the corrosion rate estimation. Even though the concrete used in the specimens had a high level of salt per unit volume of concrete, the results indicated no corrosion activity.

247 Table F.12. Corrosion Rate Estimation Label iappl (mA/m2) DE (mV) bc (mV) ba (mV) icorr (mA/m2) Corrosion Rate (µA/cm2) Rating OA_1 OA_2 OA_3 365.78 282.76 330.75 296.00 290.33 318.78 120 120 120 60 60 60 1.26 1.08 0.73 0.13 0.11 0.07 Negligible Negligible Negligible OA4_1 OA4_2 OA4_3 757.58 555.11 570.26 405.44 380.22 389.67 120 120 120 60 60 60 0.32 0.38 0.33 0.03 0.04 0.03 Negligible Negligible Negligible HVAL_1 HVAL_2 HVAL_3 602.47 433.49 496.30 399.89 352.22 371.67 120 120 120 60 60 60 0.28 0.51 0.40 0.03 0.05 0.04 Negligible Negligible Negligible HVAH_1 HVAH_2 HVAH_3 1403.08 519.70 241.89 556.78 369.56 308.11 120 120 120 60 60 60 0.03 0.44 0.66 0.00 0.04 0.07 Negligible Negligible Negligible Table F.13. Variation of Corrosion Potential During Fourth Depolarization Period Sample Time of Measurement 0 Hour (mV) 4 Hours (mV) 24 Hours (mV) BB_1 BB_2 BB_3 -102.4 -79.7 -121.4 -118.6 -93.6 -138.4 -104.3 -83.1 -123.4 OA_1 OA_2 OA_3 -328.2 -307.7 -340.0 -96.6 -108.6 -86.7 -51.2 -80.7 -40.0 OA4_1 OA4_2 OA4_3 -489.7 -442.0 -440.8 -137.6 -120.3 -112.4 -97.7 -70.1 -67.4 HVAL_1 HVAL_2 HVAL_3 -452.1 -424.3 -427.4 -116.4 -115.4 -101.8 -67.6 -76.3 -63.3 HVAH_1 HVAH_2 HVAH_3 -569.7 -315.7 -681.8 -97.1 -109.1 -140.2 -29.4 -59.9 -87.4 Fourth DEPolarization Table F.13 shows the variation of corrosion potential during the fourth 24-h depolarization period. The values presented were calculated by taking the average of all nine surface corrosion potential measurements for each sample. During the fourth 24-h depolarization period, it was observed that the corrosion potential of the control speci- mens did not change; however, all of the specimens with anodes showed a large shift in potential after the disconnec- tion of the anodes. The largest change was observed for the HVAH specimens, followed by HVAL and OA4 specimens, and finally by the OA specimens. The potential of the rein- forcing steel 4 h after disconnection averaged -112 mV for all specimens. The corrosion potential of the reinforcing steel 24 h after dis connection averaged -66 mV. Figure F.36 shows normalized values of the corrosion poten- tial during the fourth depolarization period. Table F.14 shows the corrosion rate estimation. Even though the concrete used in the specimens had a high level of salt per unit volume of concrete, the results indicated no corrosion activity. Conclusions The test results indicated that there was no corrosion in any of the specimens in the given time period. The testing fur- ther indicated that specimens with high-level, high-voltage anodes (HVAH) provided increased corrosion protection by having higher current and generating more negative poten- tial values than the low-level, high-voltage anodes (HVAL). Anodes with four times the surface area (OA4) provided more current and corrosion protection than ordinary (OA) anodes. HVAL anodes exhibited current and potential values similar to the OA4 anodes. Both high-voltage anodes and OA4 anodes provided higher current and generated more negative potential values, indicating better corrosion protec- tion than OA anodes. Recommendation Due to time constraints, the tests were terminated without observing corrosion in the specimens. Further research with an extended time frame is recommended.

248 Figure F.36. Normalized values of half-cell potential during fourth depolarization. 100.00 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 0 4 8 12 16 20 24 Co rr os io n Po te nt ia l( m V) Time (hours) Normalized values of Half cell potential BB_1 BB_2 BB_3 XP_1 XP_2 XP_3 XP4_1 XP4_2 XP4_3 HVAL_1 HVAL_2 HVAL_3 HVAH_1 HVAH_2 HVAH_3 Table F.14. Corrosion Rate Estimation Label iappl (mA/m2) DE (mV) bc (mV) ba (mV) icorr (mA/m2) Corrosion Rate (µA/cm2) Rating OA_1 OA_2 OA_3 331.32 161.54 293.71 277.00 227.00 300.00 120 120 120 60 60 60 1.64 2.08 0.93 0.16 0.21 0.09 Negligible Negligible Negligible OA4_1 OA4_2 OA4_3 728.08 528.61 512.58 392.00 371.89 373.33 120 120 120 60 60 60 0.40 0.42 0.40 0.04 0.04 0.04 Negligible Negligible Negligible HVAL_1 HVAL_2 HVAL_3 526.21 450.59 480.73 384.56 348.00 364.11 120 120 120 60 60 60 0.33 0.57 0.45 0.03 0.06 0.04 Negligible Negligible Negligible HVAH_1 HVAH_2 HVAH_3 1201.89 186.49 2597.31 540.22 255.78 594.33 120 120 120 60 60 60 0.04 1.39 0.03 0.00 0.14 0.00 Negligible Negligible Negligible