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)
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)
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)
