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Technical Publication: Assessment, Selection, and Specification of Cathodic Protection Measures in Reinforced Concrete Inrastructures and Historic Buildings

Authors: Mehrooz Zamanzadeh, George T. Bayer, Kevin Groll and Shawn McArdle

ABSTRACT

A proven methodology for providing assessment, selection and specification of cathodic protection measures in reinforced concrete infrastructures and historic buildings is described. An on-site condition evaluation survey is first required. Evaluation and survey will consist of implementation of several analysis techniques including visual examination to detect defects, petrography to determine concrete condition, and various electrochemical measurements such as half cell potential mapping, linear polarization, continuity, stray current identification and resistivity. Laboratory analysis of petrographic and corrosion product samples should be conducted by an experienced petrographic specialist. Petrographic evaluation will determine aggregate type and size, depth of carbonation, air void content and mode of deterioration if present. These will determine integrity of concrete and the best means of rehabilitation and corrosion protection. Based on the above work, determination of extent of damage and remaining service life are made. Critical questions to be answered are is the reinforced concrete infrastructure sound, and does it require repair or replacement? Consideration is given to materials selection for repair and/or replacement of the structural components. In addition to concrete repair materials, this may include alternative corrosion-resistant materials. Preliminary design and specification is subsequently undertaken of a suitable repair system, and of a cathodic protection system. Cathodic protection (CP) is a method wherein a sufficient amount of electric or impressed current (DC) is continuously supplied to a submerged or buried metallic structure to mitigate, slow down or stop altogether the natural corrosion processes from occurring. A galvanic anode cathodic protection system generates DC as a result of the natural electrical potential difference (electrochemical reaction) between the metal to be protected (cathode) and another metal to be sacrificed (anode). Case studies applying this methodology to reinforced concrete infrastructures and historic buildings are provided.

Keywords: reinforced concrete structures, historic buildings, cathodic protection, rehabilitation.

INTRODUCTION

When approaching the problem of a deteriorating reinforced concrete structure, it is necessary to visually observe and make measurements of the corrosion activity, geometry, concrete and steel materials, associated construction materials, etc., in addition to the state of corrosion which the structure has already suffered. After such observations and measurements, assessment of potential rehabilitation techniques and, as required, corrosion analysis, measures and materials to consider which will help to mitigate further corrosion deterioration of the structure for its expected life using cathodic protection and/or coatings can be recommended.

METHODOLOGY

The methodology for assessment, selection, and specification of cathodic protection measures in reinforced concrete infrastructures and historic buildings involves a clearly defined series of steps. An on-site condition evaluation survey is the first step. Samples collected on-site are subjected to laboratory petrographic and corrosion analysis. The determination of extent of damage and remaining service life is made based on the results of the on-site and laboratory investigations. In addressing the preliminary design and selection of appropriate rehabilitation measures, special consideration must be given to repair materials and systems, use of protective coatings, and design of a suitable cathodic protection system, if applicable. Laboratory electrochemical modeling of the cathodic protection technique(s) is important to determining feasibility and current requirements. The final step in the methodology is the specification for installation and operation. The methodology is described in more detail below.

On-Site Condition Evaluation Survey

The on-site condition evaluation survey includes a detailed investigation of all areas of the reinforced concrete structure and may require several hours to several days, depending upon the size of the structure. Several analysis techniques are implemented during this on-site evaluation survey, including but not limited to the following.

• Visual examination – to identify surface defects.
• Petrography – to determine concrete condition.
• Hammer/chain - to detect delaminations.
• Phenolphthalein – to determine carbonation depth.
• Chloride content – to identify chloride corrosion.
• Half cell potential mapping – to determine corrosion risk (map corrosion hot areas).
• Linear polarization – to determine corrosion rate.
• Continuity – to determine continuity/connectedness of rebar.
• Stray current identification – to determine stray current corrosion risk.
• Resistivity – to determine concrete resistivity and corrosion risk.

Concrete core samples are marked and retrieved for petrographic analysis. At least one will be from an area of rusting of the rebar reinforcement or concrete. At least one will be from an undamaged and uncorroded area of the concrete structure.

Laboratory Petrographic and Corrosion Analysis

Laboratory analysis of petrographic and corrosion product samples should be conducted by experienced petrographic and corrosion specialists. Petrographic evaluation will determine aggregate type and size, depth of carbonation, air void content and mode of deterioration if present. These will determine integrity of concrete and the best means of rehabilitation and corrosion protection.

Determination of Extent of Damage and Remaining Service Life

Based upon on-site surveying and laboratory analysis result, and employing sound materials and structural engineering principles, determination of extent of damage and remaining service life are undertaken. Critical questions to be answered here are the following.

• Is the reinforced concrete structurally sound?
• Does the reinforced concrete require repair or replacement?

Materials Selection and Coatings Application

Consideration should be given to materials selection for repair and/or replacement of the components of the reinforced concrete structure. In addition to concrete repair materials, this will include alternative materials to non-concrete auxiliary materials and maintenance coatings which may be applied to mitigate corrosion.

Design of Suitable Corrosion Protection Measures

Preliminary technical assessment is undertaken of a suitable repair system, and of a CP system for the building structure, including specification of the system. CP is a method wherein a sufficient amount of electric DC current is continuously supplied to a submerged or buried metallic structure to mitigate, slow down or temporarily stop the natural corrosion processes from occurring. The DC current corrodes a sacrificial anode when it is connected to a structure to be protected. There are two methods for supplying DC to cathodically protect a structure. They are the following:

• Galvanic or sacrificial anode cathodic protection system (SACP).
• Impressed current cathodic protection system (ICCP).

The galvanic anode cathodic protection system generates DC as a result of the natural electrical potential difference (electrochemical reaction) between the metal to be protected (cathode) and another metal to be sacrificed (anode). The sacrificing metals such as magnesium (Mg), zinc (Zn) or aluminum (Al) all have a lower more negative electrical potential with respect to carbon steel reinforcement. The current output of this system is affected by factors such as:

• Driving voltage difference between the anode and the cathode.
• Resistivity of the electrolyte (environment).
• pH factor.
• Natural or man made environmental chemistry and/or contaminates.

The impressed current cathodic protection system comprises four main components which together constitute an electrical circuit. They are as follows:

• A controllable DC power source – usually a transformer rectifier.
• An applied anode – a material placed onto or into the concrete or surrounding electrolyte to enable current flow.
• An electrolyte – normally the pore water present within the concrete, or in the case of remote anodes, also the water, soil or mud in which the anodes are placed.
• A return electrical path – normally the electrically continuous reinforcement steel to be protected.

Impressed current cathodic protection systems employ the use of electrically forced galvanic reactions to protect steel in an electrolyte (such as masonry). Anodes are installed in the masonry in strategic locations near the steel to be protected. A cathodic protection rectifier applies a DC voltage to the system with the positive lead connected to the anodes and the negative lead connected to the structural steel (cathode).

Electrical current leaves the positively charged anodes and travels through the masonry to the surface of the structural steel. Several important electro-chemical reactions occur because of this electron/ion transfer at the surface of electrodes and in the electrolyte:

• Steel surfaces receive enough protection current to mitigate or eliminate corrosion processes;

• Negatively charged corrosive ions are repelled away from the steel and pulled towards the positively charged anodes;

• Oxygen reacts with positively charged electrode (anode);

• Oxygen reduction occurs at the cathodic sites (structural steel).

The CP transformer rectifier can be powered by external power sources, such as alternating current (AC). The CP rectifier converts the input power source into DC. DC is discharged from impressed current anodes made of metals such as steel, high silicon cast iron, graphite, platinum and mixed metal oxide coated titanium. The potential current output of an impressed current CP system is limited by factors such as available AC power, rectifier size, anode material, anode size and anode backfill material. However, higher maintenance during service is required and short circuiting of anode and masonry encased steel should be taken into consideration in design and implementation of this system.

Impressed current cathodic protection systems applied to above ground structures can be applied in a number of ways depending on several important factors. The major concerns when designing an ICCP system are as follows:

• Corrosivity of environment (Presence of moisture, chlorides, and oxygen);
• Current state of corrosion of masonry-encased steel members;
• Quality of encasing masonry;
• Electrical continuity between all encased steel members;
• Total surface area of steel to be cathodically protected;
• Total electrical current required to protect encased steel;
• Protection criteria.

It is important to determine the condition of the steel beams and current requirements for the design of a reliable cathodic protection system.

Laboratory Electrochemical Modeling of Cathodic Protection

Laboratory electrochemical modeling and experimentation should be conducted on a small scale mock-up of the reinforced concrete structure to identify the most suitable cathodic protection technique(s) for corrosion control of the renovated tower. Current requirements should also be determined.

After preliminary electrochemical experimentation is conducted on sample material, a small scale laboratory simulation resembling the reinforced concrete structure will be constructed and tested using the candidate cathodic protection technique(s).

Specification for Installation and Operation

After the optimum cathodic protection technique and current requirement for the renovation is identified and laboratory simulation testing is completed, specifications for its installation and operation will be developed. Several aspects need to be considered for the selection and specification of the cathodic protection technique and system. These include the following.

• The method must be practical, safe and economical to install. The selection of the anode type is the most important consideration.
• The installed system will add a certain amount of dead weight to the reinforced concrete structure, which must be taken into account.
• The system must be physically capable of polarizing the embedded reinforcement adequately by passing a uniform, controlled current at an acceptably low voltage.
• The system components must be durable enough to withstand the installation and to fulfill the design service life.
• The installed system must not adversely affect other components or structures.
• The system should be aesthetically acceptable in the structure.
• The installed system should be easy to operate and the design should address inspection and maintenance requirements adequately.

Provision should be made for a corrosion sensor or reference electrode to monitor corrosion.

CASE STUDIES

Three case studies are presented here which applied the methodology discussed above. They are the Bok Tower at the Bok Tower Historic Sanctuary in Lake Wales, Florida, the dome of the Utah State Capitol Building in Salt Lake City, Utah, and the LOOP, LLC brine transfer pumping station in Lock Out, Louisiana.

The Bok Tower

Bok Tower is one of America ’s most unique and beautiful landmarks. The construction of the Bok Tower Historic Sanctuary in Lake Wales , Florida began in 1927 in 1927 and was completed on February 1^st, 1929 . This historic building is a beautiful tower and is the focal point of the sanctuary which houses one of the world’s finest carillons. The tower is 15.5 meters square at the base, changing form at 45.7 meters high to an octagon some 11.3 meters on a side, with sculpture design by Lee Lawrie. It is surrounded by a 4.6 meter moat which serves as a lily pond. Bok Tower ’s interior contains the Anton Brees Carillon Library, said to be the largest carillon library in the world.

The case study provides a description of design requirements and installation procedures for an ICCP system for the Bok Tower . The Bok Tower , is a masonry-encased steel framed building with marble and coquina siding. Figure 1 and 2 present photographs of the Bok Tower . The coquina brick used to cover most of the tower exterior is a porous brick made of crushed seashells and similar material. Corrosion of horizontal structural steel members caused the coquina brick faÇade and underlying masonry to separate from the tower. Areas of corrosion of the steel reinforcement are shown in Figures 3 and 4. The root cause of corrosion was found to be ingress of moisture through the porous coquina brick and from openings in the top of the tower. In addition, there were cavities present, some of which were created by plastic sheeting that was installed behind the coquina brick during a previous repair. The cavities served as the primary sites for accelerated corrosion. During recent repairs, the coquina brick and underlying masonry was removed from the front of the horizontal beams and top plate (which is connected to the horizontal beam and supports the coquina brick). The structural steel surfaces were cleaned, coated with a cementious coating, and encased with brick and mortar. New coquina brick was then fitted to the outside. Furthermore, the areas behind the coquina brick at the corners of the tower were completely encased with ASTM C 270 Type K mortar.¹

Two onsite visits in the winter of 2006 were performed to in order to explore the feasibility of application of an ICCP system for corrosion prevention of the mortar-encased steel structure. The on-site investigation identified several areas of tower composite wall that may contain voids and empty spaces due to shrinkage of the mortar. Comparative potential measurements between the surface of the coquina faÇade and encasing mortar (exposed by removal of the faÇade) confirmed these observations. Application of temporary titanium anodes and impressed current provided adequate cathodic protection for the masonry-encased steel, indicating cathodic protection is indeed applicable for this situation; provided that the coquina faÇade is bypassed as it did not serve as a continuous electrolytic path for cathodic protection.

Once it was determined that the structure was fit for application of ICCP, a mock tower section was constructed in order to help identify design specifics. Photographs of the tower mock-up are found in Figures 5 and 6. It was found that the majority of the structural steel in Bok Tower can be cathodically protected using impressed current cathodic protection and sacrificial anode/coating cathodic protection.

Bok Tower is situated in a moderately corrosive environment. It was found through testing that the steel beams are not actively corroding, likely because of the recent repairs. The masonry was found to be of adequate quality for application of cathodic protection, and the environment is moderately aggressive in that the beams are constantly exposed to moisture and a fresh supply of oxygen. All encased steel members are assumed to be electrically continuous according to schematics and observations. And finally the steel surface area and total electrical current required to cathodically protect those surfaces was calculated based on onsite and in-house testing. These requirements are discussed below.

Problematic areas on Bok Tower were identified and an ICCP system was designed in order to protect those areas. The primary areas of concern were identified as the top plate on the horizontal beams and the intersection between the vertical and horizontal beams. Other areas of concern were the web and flange area of the horizontal beams that faced outward as well as the bottom surface of the horizontal beams.

Because of the geometry of the tower and need to preserve the appearance of the exterior, a discrete anode system was designed for the ICCP system, using 11 discrete zones. Use of multiple zones allows for application of different amounts of cathodic protection as needed by each zone. Figure 7 presents a drawing of the zone layout. Other systems employ the use of ribbon, wire mesh, or coating anodes. These methods are more invasive and found to not be appropriate for use on Bok Tower . The discrete anode system will allow for installation of anodes from inside the tower. This will allow for easier installation and preservation of the decorative brick and marble exterior.

Testing and theoretical considerations revealed that the anodes needed to be applied above and below each horizontal beam to apply an adequate current on all exposed surfaces. This array allows for the target areas of steel to exhibit the 100 mV potential shift required for cathodic protection. The design criteria for the Bok Tower cathodic protection system are provided as follows.

• The approximate steel surface area to be fully protected to the 100 mV potential shift criteria is 143 m².
• Approximate steel surface to receive cathodic protection for partial corrosion mitigation is 424 m².
• The maximum required current density under worst case operating conditions is 10.8 mA/m².
• The required current density for normal operating conditions is 2.7 mA/m².
• The total number of discrete anodes required is 880.
• The total number of reference electrodes required is 43.

As the bell room at the top of the Bok Tower includes openly exposed structural steel, a SACP system employing thermal spray metallizing was selected for this location.

Utah State Capitol Building

The 90 year old Utah State Capitol Building in Salt Lake City , Utah , is undergoing a renovation and seismic upgrade in order to extend its life by another century. It is located at the top of State Street and overlooks the Salt Lake Valley . Construction on this great and beautiful building began on December 26^th, 1912 , and the building was dedicated on October 9^th, 1916 . The building is 123 meters long, 73 meters wide, and 87 meters from the base of the building to the top of the dome.

Built before seismic-resistant engineering and building codes existed, the Utah State Capitol Building has successfully withstood the loadings over the past 90 years without signs of major structural failure. However, corrosion of steel reinforcement has been taking place and requires attention.

Concrete serves as a base for terra cotta panels. Spalling, corrosion, efflorescence, and other problems are occurring in the steel reinforced concrete in interior portions of the dome, which is shrouded with an exterior copper roof. Figures 8 and 9 present photographs of the building and a close-up of the dome, respectively. Figure 10 shows some of the repair being undertaken at the dome.

As a first step in the selection and specification of a cathodic protection method to be employed in the dome renovation, an on-site corrosion survey and audit of the interior of the dome was conducted. Electrical potential measurements showed the active corrosion of the rebar in many locations. However, continuity testing for the rebar was positive, meaning that a cathodic protection system is viable for this structure. The on-site investigation and preliminary laboratory evaluation has revealed that visible internal cracking and steel reinforcement core (rebar) corrosion starts at a level just below where the external copper roof ends. Figure 11 shows a close-up photograph of the rebar corrosion.

After the optimum cathodic protection technique and current for the dome renovation was identified, work was then undertaken to develop and establish the specifications for its installation and operation. Provisions were made for a reference electrode system to monitor corrosion.

Before determination of the cause can be made for the deterioration and corrosion of the concrete/steel reinforcement, laboratory petrographic analysis of a sample retrieved on-site was required. Petrographic analysis of concrete cores showed the concrete to be of poor quality as a result of low alkalinity (carbonation), and a high water/cement ratio which resulted in a low compressive strength. The high water/cement ratio also produces a very porous concrete. The high alkalinity normally associated with concrete protects embedded steel from corrosion. However the potential for corrosion of embedded rebar will increase in the presence of low alkalinity, chloride ions and moisture. Chloride ions were found by energy dispersive x-ray (EDS) analysis in the corrosion products collected on site.

It should be noted that some of the submitted core samples exhibited more than 50% loss of thickness of rebar. It was found that cathodic protection would stop further corrosion. However, it would not compensate for load bearing of corroded rebar. Stress calculations needed to be performed to ensure the structural integrity of the reinforced concrete after repairs.

In the second phase of this project, electrochemical studies were performed on the dome concrete and steel reinforcement cores to identify the most suitable cathodic protection technique for corrosion control of the renovated dome. Figure 12 presents a schematic of one of the test configurations used in the electrochemical studies. These studies also aided in the determination of current requirements.

Electrochemical laboratory tests were specifically designed to simulate the effect of the practical application of titanium mesh and zinc spray metallized coating as anodes to the renovated (concrete added) inner surface of the Utah state capitol dome. On this basis of lower required current densities, as well as the anticipated greater service lifetime of titanium mesh (40 years) versus zinc metallized coating (10 – 15 years), titanium mesh was selected as the anode for cathodic protection of the renovated Utah state capitol building dome.

A schematic of the Utah State Capitol Building dome is given in Figure 13. Based on discussions with the lead engineering firm on the project, the following characteristics of the Utah state capitol building dome concrete were determined for the purpose of specification of the titanium anode mesh cathodic protection system to be installed.

• Estimates of the minimum and maximum distances of the rebar from the inner surface of the concrete dome.
• Additional concrete thickness added to the dome inner surface for the rehabilitation, and the distance of the rebar from this rehabilitated dome inner surface.
• Overall surface area of interior concrete, and surface area of interior concrete with severe deterioration.
• Surface area of rebar in the existing and rehabilitated concrete dome.

The request was to provide cathodic protection on an area totaling 286 m², and with use of titanium mesh anodes, a corrected minimum anode current, taking into account contact of steel structural members with concrete, as well as rebar, the total minimum required current was approximately 10 A.

Some guidelines were presented for construction and installation of the cathodic protection system, including the following topics.

• Repair of the damaged concrete in the dome.
• Additional petrographic analysis of the dome concrete.
• On-site testing to verify current requirements.
• On-site testing for verification of the existence of electrical continuity in the steel-bar network in the existing dome structure and in the concrete addition.
• On-site testing to verify discontinuity of rebar with other foreign metallic structures in the dome, including copper roofing itself.
• On-site testing to conduct potential mapping to identify corrosion “hot spots.”
• Installation of reference cells in each section.
• Installation of a predestinated activated titanium mesh in each section.
• Bonding of all sections of the mesh.
• Placement of the concrete overlay.
• Completion of the system electrical wiring.
• Rectifier quantity and placement.
• Start-up of the CP system.
• Post start-up and operation monitoring.

The specification covered distributed titanium mesh anodes which are placed on a blasted, cleaned surface and then covered with a concrete overlay. It was determined that NACE Standard RP0290-2000, “Standard Recommended Practice: Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures,”² should be followed at all times.

The approved anode system was a titanium mesh anode system. Titanium mesh anodes systems consist of expanded titanium mesh coated with a precious metal oxide catalyst which is fastened to a prepared surface and overlaid with concrete to provide a new riding surface. These systems are designed and installed such that the average current density at the surface of the anode does not exceed 110 mA/m².

The titanium mesh anode recommended may be either one of two types: an anode with a current rating of 24 mA/m², or an anode with a current rating of 40 mA/m².

Several material and construction and installation related specifications were covered. Some important points that should be noted are as follows.

• All wiring must be done in conformance with the latest version of the proper electrical codes.
• Titanium mesh anode must not contact any existing steel structure, rebar, or anchors.
• Titanium mesh is divided into four independent anode units, or electrical zones, employing one rectifier with four terminals. The rectifier should be autopotential and IR compensated. The rectifier should be rated at 20 A and 100 V. A minimum of eight reference electrodes should be employed, with a minimum of two reference electrodes per zone.
• Titanium ribbons should be welded to mesh in vertical and horizontal directions; then lead to titanium wire should be connected to the positive terminal of the rectifier.
• Prior to installation, on-site testing must be performed to verify theoretical calculations and to confirm discontinuity between the rebar and the copper roof and other steel structural members.
• Consideration should also be given to perform petrographic analysis on other parts of the dome to test the integrity of the concrete and make sure these sections do not exhibit carbonation or accelerated corrosion of the rebar.

LOOP, LLC Pumping Station Concrete Platform

A corrosion assessment was undertaken of the pumping station concrete platform in the brine reservoir at the LOOP , LLC oil transfer station in Lock Out, Louisiana . This is one component of a major pipeline system t o transport crude oil from the eastern Gulf Coast to western Gulf Coast refiners. The pipeline carries foreign crude supplies from South America , West Africa and the Middle East , and domestic crude produced in the Gulf of Mexico . In this role, it is a critical component of the U.S. energy infrastructure. Figure 14 is a photograph of the concrete platform.

On two days in August 2004, field surveys were performed on the reinforced concrete pumping station platform and associated structural steel components. The purpose of this investigation was to assess and evaluate the condition and current corrosion characteristics of the reinforced concrete platform. Based on the stated desire for additional extended service of the structure, recommendation was made as to remedial measures that should be undertaken to mitigate the effects of corrosion on this structure and extend service life.

A variety of field tests were carried out on immersed, splash zone and atmospherically exposed components of the structure. These included concrete piles, horizontal and vertical painted load bearing members, pumping station components and reinforced concrete. Field tests included visual and photographic surveys, delamination detection, electrical potential surveys, measurements of concrete and water corrosivity towards steel and zinc, measurements of electrochemical potentials, corrosion mapping, and stray current testing. Figure 15 is a drawing of the pumping station platform with sections marked for corrosion potential mapping. Figure 16 presents a photograph of corrosion on one of the concrete piles. Figure 17 provides a photograph of corrosion along the edges of load bearing support members.

Core samples of concrete were analyzed in the laboratory for chloride content, compressive strength and petrographic analyses. A corrosion attack evaluation by scanning electron microscopy was also performed on samples of reinforcing steel strands.

The most significant findings of the on-site and laboratory investigation indicated that the load bearing painted steel members surveyed exhibited corrosion problems to varying degrees. The degradation of paint coatings resulted in accelerated corrosion of the steel in these areas. For the most part, the coating of the steel members failed along the corners and edges, most likely because of low coating thickness. This caused active corrosion at the edges, which needed to be addressed. The reinforced concrete exposed to salt spray under the platform also showed signs of corrosion attack and cracking due to corrosion of the steel strands. Other concrete surfaces and structures surveyed showed little or no evidence of corrosion.

Four concrete core samples were obtained at the site and identified as: core number 1-from good area; core number 2-from bad (salt spray) area; core number 4-from bad area; and core number 5-from good area. Compressive strength testing, in accordance with the methods of ASTM C39/C39M-05e1³, was performed on core number 2. The compressive strength was determined to be 23.4 MPa with a water/cement ratio of approximately 0.57-0.60.

A quantitative chemical analysis for pH and water soluble chlorides was also performed. The results indicated 1.53 to 0.039 weight percent chlorides from the top surface to 12.7 mm from the top surface. There was no evidence of chlorides on the steel strands indicating chlorides were not present next to the reinforced strands on the top surface of the concrete platform.

A core sample was cut and then broken open to expose the steel, seven wire strand reinforcement. The reinforcement strand was examined visually using a low power optical stereomicroscope. The individual steel wires exhibited a very thin film of corrosion products, but no severe corrosion or pitting. No indication of section thickness loss or chlorides on the wire strand reinforcement was observed. This particular core was chosen for analysis because it had been taken from an area that was in close proximity to the pumping station. This close proximity, we would assume, would expose the concrete core to high amounts of salt spray.

The petrographic analysis of the cores removed from salt sprayed areas and good areas (top section near the pumping station suggested that the concrete was in good condition. The compressive strength of the concrete, pH, degree of carbonation, as well as the chloride content all indicated that the concrete was sound and in good condition

At this time, no signs of severe degradation or corrosion of the steel reinforcement members were observed on the top surface of the concrete slab. However, the steel reinforcement beneath the platform exhibited corrosion attack due to wetness and chloride exposure from the brine and pumping action.

Based on the stated desire for additional extended service of the concrete platform, a cathodic protection system using sacrificial thermal spray zinc/aluminum coating was recommended. The surface sacrificial galvanic coating would be applied where the reinforcement in the concrete exhibited accelerated corrosion and red rust, and in areas where the reinforced concrete exhibited cracking due to corrosion of steel reinforcement. Specifically, it was recommended to selectively apply the sacrificial anodic coating on vertical and horizontal atmospheric and splash zones beneath the concrete platform at the pumping station and to the load bearing member areas. Applicator experience in salt/brine environments and surface preparation of concrete are very important and should be taken into consideration. The coating applicator procedures should be qualified and observed by third party NACE Certified Corrosion /Coating inspectors.

The overall conclusion from these studies is that the concrete platform in the Brine Reservoir at the Loop , LLC Oil transfer station in Lock Out, Louisiana is in relatively good condition. However, in view of the extended period of additional service life that is desired for this structure, maintenance painting should be performed and a sacrificial coating should be applied to locations that the steel reinforcement exhibits accelerated corrosion and red rust. The following procedures were recommended:

• Apply an approved three coat system to all metallic surfaces.
• Replace stainless steel bolts with galvanized steel to prevent stress corrosion cracking.
• Apply thermal spray zinc/aluminum coating to all vertical and horizontal concrete surfaces that are beneath the platform and are exposed to salt spray and/or exhibits staining, red rust and cracking.
• Install test stations to monitor corrosion activity in immersed, splash zone and atmospheric areas.

Figure 18 is a schematic representation of the recommended corrosion mitigation method for the concrete piles and decking, with positioning of reference electrodes

It was recommended that the program begin as soon as possible and be repeated every seven to ten years, based on the condition of the paint coating and sacrificial anodic coating. Applicator experience in salt environments and surface preparation of the concrete are very important factors that should be taken into consideration. The coating application procedures should be approved by a NACE Certified Corrosion/Coating Specialist.

Consideration was also given to adopting a long term, continuing program for the evaluation and monitoring of cathodic protection systems on concrete piles, atmospheric and splash zone areas. The monitoring program, performed biannually, would consist of measuring pile to brine water potentials at each pile and determining the effectiveness of applied sacrificial coating in order to verify that cathodic protection systems are functioning properly.

CONCLUSION

As shown by the case studies presented in this paper, a standardized methodology for assessment, selection, and specification of cathodic protection can be applied to reinforced concrete infrastructures and historic buildings. An on-site condition survey is the first and critical step, both in its own right in assessing the extent of damage and necessary repair, as well as in collecting samples and information required for the selection and specification of cathodic protection. Although not widely considered, lab scale electrochemical modeling employing materials used in the actual reinforced concrete structure will be constructed in appropriate geometry and tested using candidate cathodic protection technique(s). Such lab scale electrochemical modeling provides invaluable data for the final selection and specification of the cathodic protection method.

REFERENCE

1. ASTM Standard C270-06, “Standard Specification for Mortar for Unit Masonry,” (West Conshohocken , Pennsylvania : ASTM International, 2006).

2. NACE Standard RP0290-2000, “Standard Recommended Practice: Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures,” ( Houston , Texas : NACE International, 2000).

3. ASTM Standard C39/C39M-05e1, “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, (West Conshohocken , Pennsylvania : ASTM International, 2005).