Non Destructive Detection of Fractures in Prestressed & Post-tensioned Cables
Post-tech Cable Break Detection System (CBD) is a non-destructive method for locating fractures in pre-stressed cables and both bonded and unbonded post-tensioned cables. To read entire article, click here.
Galvanode DAS case studies presented during Australasian Corrosion Conference 2009
Galvanic Protection for Reinforced Concrete Bridge Structures: Case Studies and Performance Assessment – A paper presented to the Australasian Corrosion Conference 2009 by Chris Ball and David Whitmore. To read the complete article click here.
Galvanode DAS Featured in Concrete International
Vector’s Galvanode® DAS, a versatile distributed anode system, was recently featured in the September 2009 edition of Concrete International Special Products & Practice Showcase. To view the article click here.
Ten Year Results Of Galvanic Sacrificial Anodes In Steel Reinforced Concrete
Zinc sacrificial anodes have been included in patch repairs to steel reinforced concrete structural elements suffering from corrosion since the mid-nineties. A number of these anode-containing patch repairs have been monitored over time. One of the first monitored sites was a locally repaired cross beam of a bridge structure in Leicester, UK, which has this year completed 10 years of service. Read more.
Ageing Port Infrastructure Gains New Life
The corrosion of reinforced steel in concrete structures is a global problem. A number of highly technical repair materials are now available to repair concrete structures suffering steel corrosion damage of reinforcing steel. The June 2009 issue of World Port Development provided an overview of protection systems for reinforced concrete piers and wharves. For additional information click here.
Cementitious Matrix is Used to Bond High-Strength Polymeric Mesh to Concrete and Masonry, Fallis
Fiber-reinforced polymer (FRP) systems are now widely used for retrofit and repair of concrete and masonry. The development of these systems has allowed repair and strengthening projects to be performed that, in the past, would not have been possible. Their benefits are well known and include a high ratio of strength to added weight, high durability, and ease and flexibility of installation.
FRP systems, however, are not without their drawbacks. Recently, Ruredil introduced a new fiber-reinforcement system that maintains the benefits of traditional FRP systems while overcoming some of their drawbacks. This product consists of a polyparaphenylene benzobisoxazole (PBO) mesh (Ruredil X Mesh Gold) and a stabilized, inorganic, cementitious mortar matrix (Ruredil X Mesh M750) designed to connect the mesh to concrete and masonry substrates. The unique structure of the PBO fiber allows it to bond directly to the mortar matrix, eliminating the need for an epoxy resin to bond the fiber to the concrete or masonry substrate. (read more)
Long-term Performance and Versatility of Zinc Sacrificial Anodes for Control of Reinforcement Corrosion, Sergi, Simpson & Potter
Since its development in the mid-nineties, numerous installations of the Fosroc zinc sacrificial anode have been carried out in repairs to steel reinforced concrete structural elements suffering from corrosion. From these, more than a dozen sites have been thoroughly monitored in the UK and worldwide. Results so far have been very encouraging with current densities ranging between 0.8 mA/m2 and 10 mA/m2 of steel surface depending on the type of application which includes cathodic prevention, corrosion control and cathodic protection. These levels of currents were shown to be sufficient to overcome any further visible corrosion of the steel reinforcement extending the service life of the repairs significantly. Some of the early trials have been monitored for nearly ten years now. This presents an opportunity for the results to be analysed and the performance of the sacrificial anodes to be critically assessed medium to long term. This paper reviews the performance of the anodes in terms of current output and steel polarisation levels over the years. The prospects of a further recently developed improved sacrificial anode system achieving substantially improved performance are reviewed and discussed. (read more)
Corrosion of Steel in Concrete & Assessment Techniques, Sergi
Concrete is a porous material whose pores contain an electrolyte made up primarily of sodium and potassium hydroxides. Steel reinforcement is normally protected in such an electrolyte owing to the formation of a dense and uniform passive oxide film. Carbonation of the concrete (neutralisation of the alkali constituents by CO2 gas from the atmosphere), or infestation of the concrete with salt from seawater or from deicing agents leads to the breakdown of the protective oxide film and to corrosion of the steel. Corrosion of steel in concrete is an electrochemical process whereby anodic and cathodic reactions occur simultaneously on the surface of the steel resulting in the dissolution of the metal at the anodic sites. (read more)
Corrosion Investigation & Testing of Post-Tensioned Cables, Fallis & Arnesen
The Post-Tech Corrosion Evaluation (CE) System provides a method for evaluating the potential for corrosion activity in un-bonded post-tension cables that if left untreated can be the cause of structural concerns with the un-bonded post-tensioned structures. This system has been successfully performed on several hundred structures in the past 15-years. It provides a method to restore the wet post-tension cables back to the environment for which they were originally designed. Un-bonded post-tensioned cables can not only be evaluated for their potential for corrosion, but also for identifying possible locations for un-bonded post-tension strand failure and the possible related structural deficiency.
The Post-Tech Cable Break (CB) system relies on the remanent magnetism method (RM-Method) to identify damaged or unsafe high strength individual or bundled pre-stress strands. This is a non-destructive test for evaluating the magnetic field or flux of externally magnetized tendons. Characteristic fracture readings of the magnetic leakage field are used to evaluate the extent of damage or amount of steel cross-section loss of the cables, which could include single or multiple wires in the strands. Wire or even strand fractures can happen abruptly and there are often no external visible signs of this type damage. (read more)
Embedded Galvanic Anodes for Targeted Protection in Reinforced Concrete Structures, Ball & Whitmore
Corrosion of reinforcing steel in concrete is a major cause of structure maintenance and repair. Oxidation at the anodic sites on the steel reinforcement causes expansive forces that leads to visible concrete distress such as rust stains, cracks, spalling, or delaminations. Corrosion can also cause delaminations in the concrete cover (which may not be visually apparent), potentially with large sections of concrete dislodging from the structure. Additionally, loss of section due to reinforcement corrosion can cause structural issues. Advancements in concrete repair methods and corrosion mitigation systems have given structural engineers many options to repair and extend the service life of actively corroding structures. Today, most structures suffering from corrosion can benefit from some level of electrochemical corrosion protection.
In some cases, a global protection strategy using electrochemical chloride extraction, impressed current cathodic protection, or galvanic protection is a preferred solution. Global protection should be considered if: 1) a long service life is desired; 2) corrosion activity is widespread; 3) the structure is considered to be critical in nature; 4) access is difficult and/or cost of future repairs are high; or 5) a high level of protection is required over large areas. n other cases, corrosion is not widespread or budget limitations prevent a more comprehensive approach from being implemented. In these cases, implementing a targeted corrosion mitigation approach is generally preferred rather than not providing any protection whatsoever. Targeted corrosion protection can be economically implemented to provide an extension of service life at a moderate incremental cost and reduce the risk of serious corrosion damage.
For almost a decade, embedded galvanic anodes in a discrete or “point” form have been used to provide localized corrosion prevention around concrete repairs. Embedded discrete anodes are installed around the perimeter of the concrete repair as close as practical to the patch edge. The anode units are prewet and tied directly to the reinforcing steel. The anode spacing is dependent on the amount of steel protected, but is generally in the range of 12 to 24 in. (305 to 610 mm).
For over 5 years, galvanic anodes in a ribbon or strip form have been used to provide protection in reinforced concrete. As opposed to discrete or point anodes, these anodes are referred to as distributed anodes and are provided in various shapes and lengths up to 7.5 ft (2.3 m). Distributed anodes are placed across the surface of the concrete to be protected then embedded in a reinforced concrete jacket or overlay. The distributed anode systems are used to provide galvanic protection over a larger area but can be easily used to protect small structural elements such as a single pile, column, or wall. This type of system can also be referred to as a galvanic encasement. (read more)
Maintenance, Repair, & Rehabilitation of Concrete Bridges, Aspire Magazine
Two Vector projects were featured in the Maintenance and Repair section of the Winter 2009 issue of Aspire Magazine. Click here to learn more about how Ohio DOT utilizes Galvanode® DAS to extend the life of bridge abutments and how Norcure® ECE was utilized to preserve the Historic Rainbow Bridge in Idaho. (read more)
Galvanic Corrosion Protection of Reinforced Concrete Structures, Ball & Whitmore
In the past 10 years, there have been significant advancements in galvanic anode technology for reinforced concrete structures. Today, galvanic protection is the most commonly utilized form of corrosion protection for reinforced concrete in North America. The popularity of galvanic systems is due to many factors including ease of installation and little or no on-going system maintenance costs.
Distributed galvanic anode systems are used to provide targeted protection to specific structural elements as well as global protection to large areas in both marine and non-marine exposure environments. Examples of distributed galvanic protection technology include humectant-activated arc spray zinc and galvanic jacketing systems
Recent installations for distributed anode systems include a multi-million dollar rehabilitation of four cargo loading piers at Cape Canaveral, Florida. This project utilized a range of galvanic protection systems targeted to the varying needs of the structure. Distributed protection was utilized to protect over 5,000 m2 of prestressed concrete decks and 668 prestressed concrete piles in saltwater. (read more)
Electrochemical Treatment: Extending the Life of a Historic Viaduct Structure, Ball
Completed in 1915, the historic 12th Street Trafficway Viaduct is a 2,300-foot long reinforced concrete structure that was constructed to link the industrial district in the bottom land along the confluence of the Missouri and Kansas rivers to the commercial district along the bluffs 200 feet above. The Viaduct is undergoing a major restoration program to extend the service life of the 90-year old structure. In 2005, ECE was used to treat the large concrete columns as part of an overall rehabilitation. (read more)
Long Term Behaviour of Ceramic Tubular Shaped Anodes for Cathodic Protection Applications, Sergi, Simpson & Hayfield
Ceramic tubular electrodes have been in use successfully as discrete anodes in impressed cathodic protection (CP) applications for several years tolerating current densities several times higher than most commercially available anodes. They owe their success to the stable highly conductive nature of the particular titanium suboxide used. Although stable, the titanium sub-oxide ceramic is known to slowly polarise when subjected to extreme cathodic current densities so it was important to determine their longevity under such strong polarising conditions. A long term programme was, therefore, initiated in 1994 with the objective of monitoring the performance of anodes embedded in steel reinforced concrete blocks over a period of between 7 and 12 years under a range of polarising levels. The work was supplemented by subjecting tubular anodes to the NACE Standard Test Method (NACE Standard TM0294-2001) at normal and four times normal current densities by surface area of the anode at equivalent charge levels of up to 100 years at 110mA/m2 and 900mA/m2. Electrochemical results indicated a very good performance of the anodes over the test period and showed clearly that any polarisation of the anodes was acceptably low. (read more)
Innovative Corrosion Evaluation System for Unbonded Post-Tensioned Cables, Fallis, Ball & Moad
Unbonded post-tensioned tendons may corrode for a number of reasons, even though they are encapsulated by a plastic duct. This is primarily due to voids in the protective grease, which allow moisture to accumulate adjacent to the post-tensioned tendon. Corrosion may go undetected for years until eventually significant structural deterioration, leading to a loss in structural capacity and, eventually, extensive and costly repairs. Increasingly, however, cases have been reported where corroded (failed) cables have erupted from the concrete, thus also posing a risk of damage or injury from ejecting cables, falling concrete, and/or dislodged claddings.
Existing methods typically used to evaluate corrosion of steel in concrete structures such as half cell corrosion potentials and corrosion rate testing are not practical to use on these types of unbonded post-tensioned structures due to the presence of the non-conductive plastic ducts. In response to the need to determine the probability of corrosion activity within unbonded post-tensioned cables, the Post-Tech® PT Corrosion Evaluation Method was developed. (read more)
Galvanic Protection for Reinforced Concrete Structures, Whitmore & Ball
Active corrosion mitigation systems for reinforced concrete structures can be defined as methods that provide a protective electrical current to reinforcing steel embedded with the structure. These types of systems fall into three broad categories:
1. Electrochemical treatments;
2. Impressed current cathodic protection; and
3. Galvanic corrosion protection.
Electrochemical treatments such as chloride extraction and realkalization provide a high level of current for a short duration to create a passive environment around the concrete/reinforcing steel interface. Impressed current systems use permanently installed anodes that distribute electrical current provided by an external power source. These systems provide a high level of control over the amount of current delivered, but the electrical systems must be maintained over time. Galvanic systems provide protective current through the installation of dissimilar metals (also known as sacrificial anodes), which corrode preferentially to the metal to be protected. Since galvanic systems operate naturally without the need for an external power source, they provide a low maintenance approach that is economical for many structures. (read more)
Installation of Embedded Galvanic Anodes, ACI Committee E706
The ACI E706 education committee on Repair Application Procedures, has published a field guide for installation of embedded galvanic anodes into concrete structures. (read more)
Innovative Corrosion Mitigation Solutions for Existing Concrete Structures, Ball & Whitmore
Reinforced concrete has developed a strong reputation as a versatile, durable and economical building material. However, when concrete is subjected to aggressive environmental conditions, repair and maintenance is required over time to keep the structure in a serviceable and safe condition. I
n recent years, the range of corrosion mitigation systems provides engineers and owners with more options to mitigate corrosion and extend the service life of existing structures. Various types of electrochemical corrosion mitigation systems (including electrochemical treatments, impressed current cathodic protection, and galvanic protection) and an overview of the various levels of protection offered by electrochemical corrosion mitigation technologies (corrosion prevention, corrosion control, cathodic protection and corrosion passivation) is presented.
Project reviews detail the application of certain specialised technologies including electrochemical treatments (re-alkalisation and chloride extraction), targeted corrosion control with embedded galvanic anodes, and galvanic cathodic protection using embedded strip anodes and humectant-activated zinc metalising. (read more)
Corrosion Management: Selecting a Corrosion Mitigation Strategy for Existing Concrete Structures, Whitmore & Ball
According to a recently completed study by the U.S. Federal Highway Administration, the annual direct cost of steel corrosion to the U.S. economy is estimated at $276 billion, or 3.1%, of the U.S. Gross Domestic Product (GDP). If indirect costs such as loss of productivity are included, the annual cost is conservatively estimated at $552 billion, or over 6% of GDP. While these statistics are specifically related to the overall cost of corrosion, some estimates indicate that up to 30% of this total is related to corrosion in concrete structures.
Many engineers and owners, facing rising maintenance costs, recognize the significant incentive to protect existing structures from future corrosion damage by considering the use of corrosion mitigation systems. Selecting the appropriate system is based on many factors, including the amount and level of existing chloride contamination or carbonation, amount of concrete damage, level and location of corrosion activity (localized or widespread), environmental exposure conditions, expected service life of the structure, and the cost and design life of the corrosion protection system.
Active corrosion mitigation systems (defined here as systems that supply a protective current to the reinforcing steel) generally fall into three performance categories: corrosion prevention, corrosion control, and cathodic protection. These systems are similar in that they all provide a protective current to the reinforcing steel to mitigate corrosion activity. This article describes the differences in these systems in terms of the intended Corrosion Management application and the intensity of the protective current required to achieve the mitigation objective. (read more)
Norcure® and Galvashield® Extend Service Life of I-480 Bridge, Bridge Builder Magazine, 2004
Constructed in the early 1970’s, the mainline structure of the I-480 viaduct through downtown Omaha, Nebraska to the Missouri River consists of 1.5 miles of concrete deck and steel box girders supported by 66 large conventionally reinforced concrete piers. By the mid-1990s, the 30 year-old structure was experiencing deterioration of the concrete deck and concrete substructure. This deterioration was due to chloride-induced corrosion of the reinforcing steel.
In 2002, Norcure Electrochemical Chloride Extraction was used on twenty-six of the piers with the highest chloride contamination levels (approximately 16,000 ft2) and Galvashield XP embedded galvanic anodes were used in the patch repairs on the remaining piers. All piers were then coated to prevent future chloride contamination. (read more)
Corrosion Mitigation Systems for Concrete Structures, Ball & Whitmore
The Florida coast provides one of the most corrosive environments in the world and is an excellent test area for corrosion mitigation systems. Elevated chloride levels from sea spray combined with high temperatures and humid conditions provide a very corrosive environment. In this type of situation, typical “chip and patch” repair programs can show signs of patch-accelerated corrosion in as little as 2 to 3 years.
In June of 2000, a condominium on the east coast of Florida exhibiting concrete spalling from patch-accelerated corrosion was selected for theapplication of an embedded galvanic anode system. The purpose of the installation was to reduce the level of corrosion activity and to cost-effectively increase theservice life of the chloride-contaminated balconies and walkways. (read more)
Galvanic Protection Focused on Concrete Repairs, Whitmore & Abbott
The product of a vast and aging concrete infrastructure has been an industry that is continually searching for new and improved methods of rehabilitation rather than outright replacement. While rehabilitation is often the most cost-effective strategy, these cost savings rely upon achieving durable, long-lasting repairs. The deterioration caused by the corrosion of reinforcing steel in concrete has been recognized as one of the greatest, most costly challenges facing many owners today.
Embedded Galvanic Anodes are a new twist on a time-honored method of corrosion protection. By incorporating these small, zinc-based anodes into concrete repairs, the durability of the repairs can be enhanced by 10 to 15 years. (read more)
Sacrifical Anodes for Cathodic Protection of Reinforcing Steel Around Patch Repairs Applied to Chloride-Contaminated Concrete, Sergi & Page
When steel reinforcement suffers localised corrosion in chloirde contaimated concrete, the most anodic regions of the metal effectively provide cathodic protection to the bars in adjacent cathodic areas. If conventional patch repair is applied to the structure, this form of adventitious cathodic protection is removed and bars which were previously behaving as cathodes in moderately contaiated areas may be transformed to anodes of cells, coupled to cathodic steel in the repaired areas. This paper demonstrates the effectiveness of combining patch repair with embedded sacrificial anodes as a means of providing continuing protection to the surrounding reinforcing bars. (read more)
