Protection Of Steel In Concrete Research Articles

Cathodic protection of precast, prestressed multistory car park slabs, using a surface applied galvanic zinc layer anode

A surface applied galvanic Zinc Layer Anode (ZLA) system was installed on a multistory carpark structure to provide cathodic protection to the soffits of the prestressed hollow concrete slabs, which were suffering from chloride induced corrosion deterioration. This paper evaluates the cathodic protection system performance against the international standard for Cathodic Protection of Steel in Concrete, ISO 12696 [13], 17 months after commissioning. A surface applied galvanic Zinc Layer Anode was selected to provide cathodic protection, as this offered a low risk of exceeding the hydrogen embrittlement potential and provided a unique application approach, which was compatible with the hollow slab construction. During the pilot phase, a total of 40 m2 of ZLA was applied into two anode zones and monitored for a month, to prove concept and system performance. Following the pilot phase the remainder of the cathodic protection works were completed, extending to a total concrete area of 320 m2. The installed system was provided with embedded reference electrodes and wired to enable full performance evaluation as per the requirements of ISO 12696. Three battery powered web-based monitoring devices were used for remote system monitoring and performance assessment. The initial performance data following 17 months of operation, identified that all 12 reference electrodes installed across the 6 anode zones all met the 100mV depolarization criteria within a 24-hour period, as per the requirements of clause 8.6b of ISO 12696. The anode to cathode current was also recorded continuously over this operational period and used to evaluate environmental effects and predicted actual anode service life.

Long term performance of reference electrodes for cathodic protection of steel in concrete

This paper will report on long term behaviour of potential sensors used in cathodic protection of steel reinforcement in concrete. Cathodic protection (CP) systems, both impressed current CP (ICCP) and galvanic CP (GCP), need regular testing to establish the quality of protection. In addition, ICCP may require adjustment of output voltage or current. Various types of potential sensors have been used in relatively large numbers, comprised of true reference electrodes (RE) based on silver/silver chloride or Mn/MnO2 and decay probes (DP) based on a.o. activated titanium. Failures may occur due to loss of contact, drying out or cable defects. Test methods for potential sensors are discussed. Monitoring of about one hundred CP systems with several thousands of potential sensors over more than ten years allows to analyse their performance and failures. It appears that limited numbers of potential sensors fail over time, but in some cases an insufficient number of working potential sensors are left to properly monitor a CP system or zone. It is recommended to install more potential sensors than strictly needed in order to allow for failures and to maintain testability and save the high cost of installing new potential sensors later.

A Historical Review of Impressed Current Cathodic Protection of Steel in Concrete

This paper reviews the history of the development of impressed current cathodic protection of atmospherically exposed reinforced concrete from the first trials in 1959 on bridges to recently installed systems on a wide range of structures around the world. The paper covers the research efforts, anode developments, control systems and monitoring sensors which are reviewed and their evolution explained. The research into the potential and actual side effects of cathodic protection currents in concrete are summarised. The development of standards and guidance on impressed current cathodic protection is also reviewed.

Galvanic chloride extraction by an embedded zinc anode: Ion distribution mapped by laser induced breakdown spectroscopy (LIBS)

An important aspect with regard to the service life of zinc based galvanic anodes and the durability of the corrosion protection of steel in concrete is the “galvanic chloride extraction”. Chloride ions move in the electric field generated by the current, flowing between the galvanic anode and the cathodic steel. Migration leads to an accumulation of anions, e.g. chloride ions, at the anode and depletion of chlorides near the steel rebar surface. The ion migration was studied on steel reinforced concrete specimens admixed with 3 wt.% chloride/wt. cement and galvanically protected by a surface applied embedded zinc anode (EZA). The zinc anode was embedded and glued to the concrete surface by a geo-polymer based chloride free binder. The EZA was operated over a period of 1 year and the ion distribution between anode (EZA) and cathode (steel reinforcement) was studied by laser induced breakdown spectroscopy (LIBS) after 5 months, 7 months and 12 months. The results show that chloride ions efficiently migrate in the direction of the zinc-anode and accumulate there. Chloride distribution in the EZA correlates with the distribution of zinc ions generated by the anodic dissolution of the zinc anode in the binder matrix. The microstructure of the binder matrix and its interface to the zinc-anode are studied by REM/EDX – preliminary results will be reported.

Electrochemical behavior of zinc layer anodes used for galvanic protection of steel in reinforced concrete

Steel corrosion is the most common reason for the premature deterioration of reinforced concrete structures. Consequently, cathodic protection of steel in concrete has been substantially developed during the past two decades. In particular, galvanic protection consists in generating a natural macrocell corrosion system in which a sacrificial metallic anode (zinc, typically) is involved to apply a cathodic polarization to the corroding steel layout, in order to mitigate or annihilate the corrosion kinetics. Whether the general principle of cathodic protection is not questionable, the global design process can be significantly improved by increasing the knowledge on electrochemical behaviours of the different components of the protecting system. Regarding zinc anodes in concrete, the literature is very scarce. The time evolution of such systems is also not rigorously addressed, aging effects are systematically ignored and zinc anodes are usually considered as non-polarizable and inert over time. In this paper, the polarization response of a zinc layer anode (ZLA) in concrete electrolyte and its time evolution are studied. The results show a rapid evolution of the ZLA behavior, once the protecting system is connected to steel reinforcements. Moreover, the characterization of ZLA provided relevant electrochemical properties for the numerical design of galvanic protection systems.

Assessment of cathodic protection applied to above ground reinforced concrete

Standard practice allows the use of developing expertise in the assessment of cathodic protection of steel in concrete. This work sets out a theoretical and empirical basis for such an assessment. Assessment may be based on the observation that, at protection current densities typically used in reinforced concrete, the degree of polarization provides an indication of steel corrosion risk. An example is, a steel polarization of 55 mV or more achieved by a protection current of 5 mA m−2 or less is indicative of passive steel reinforcement. Such risk assessment criteria are supported by both theory and practice. Polarization is generally a consequence, not a cause, of steel passivity in concrete. The removal of chloride from, or the generation of hydroxide at the steel surface dominate the restoration of steel passivity. Flexibility over the degree of polarization required in cathodic protection systems may be used to address adverse effects associated with the delivery of protection current.

A Review of Corrosion and Protection of Steel in Concrete

Corrosion of reinforcement is one of the major durability challenges which leads to a reduction in the design life of reinforced concrete. Due to an increasing demand for longer service lives of infrastructure (typically 100–120 years) and the high cost involved in building and maintaining it, the repair of concrete structures has become extremely important. This paper discusses mechanism of corrosion in reinforced concrete and its thermodynamic and kinetic behaviour. It also presents and compares different corrosion prevention and protection techniques available and recommended by BS 1504-9:2008, including the use of corrosion inhibitors, alternative reinforcement, steel and concrete coating and electrochemical techniques. It is concluded that the electrochemical techniques are more effective than conventional methods.

Book review

Cathodic Protection of Steel in Concrete and Masonry, second edition

A Study of Natural Pozzolan Mortars Exposed to Sulfate as Energy Efficient Building Material

Reinforcement corrosion is one of the main causes of concrete deterioration. The steel in concrete is naturally protected from corrosion by the presence of a passive film formed through the high alkalinity of concrete. A technique to improve the protection of steel in concrete is the inclusion of mineral additions. Natural pozzolan (NP) from Beni-Saf is a mineral addition that is abundant in western Algeria. The experiment was conducted on mortar specimens, containing steel bars and exposed to the aggressive solutions of Na2SO4 and MgSO4. The status of reinforcement is periodically monitored by measuring the electrochemical potentials and the corrosion rates by the technique of linear polarization resistance (LPR) and also the thermal conductivity was evaluated. The test results show that natural pozzolan significantly affects the physical properties of mortars, improves the corrosion resistance of mortars containing up to 20% of natural pozzolan and reduces the thermal conductivity.

Zinc-Rich Paint As Anode for Cathodic Protection of Steel in Concrete

This paper describes the findings of the experimental works undertaken to investigate the performance of zinc-rich paint (ZRP) to provide cathodic protection to chloride-contaminated reinforced concrete (RC) structures. The program of experimental works was designed and conducted to assess four principal properties, viz (1) conductivity, (2) adhesion with concrete (short term and long term), (3) durability, and (4) electrochemical polarization. These properties considered together define the ability and effectiveness of the materials to act as an anode for impressed current cathodic protection. The research findings indicated that a specific proprietary ZRP product showed that optimum conductance was obtained with three coats producing a 280-320 μm thickness, with good adhesion to the concrete substrate, in which values obtained ranged between 1.65 and 3.5 MPa with and without applied current. It was capable of withstanding/supporting high levels of current, i.e., more than 300 mA/m², and the service life of the ZRP coating was estimated to be well in excess of 20 years at an applied current density of 10 mA/m².

Conductive mortar as anode material for cathodic protection of steel in concrete

The behavior of a new type of secondary anode material made of carbon fiber reinforced cement used for cathodic protection of steel in concrete was studied. The mechanical, electrical and electrochemical properties of this conductive mortar were investigated. Results indicate that the addition of carbon fiber enhances the strength and ductility of the mortar, as well as the electrical property. The anodic polarization behavior was tested on specimens immersed in aqueous solutions of saturated Ca(OH)2 in the presence or absence of 3% NaCl. Based on impedance measurements the electrochemical parameters of conductive mortar were calculated. It is shown that the investigated conductive mortar can be used in cathodic protection of reinforced concrete. The study also shows that the optimum fiber content in mortar should be in the range from 0.5 vol% to 0.7 vol%.

Cathodic protection of steel in concrete using magnesium alloy anode

Corrosion of steel embedded in concrete structures and bridges is prevented using cathodic protection. Majority of the structures protected employ impressed current system. Use of sacrificial system for the protection of steel in concrete is not as widely employed. The use of magnesium anodes for the above purpose is very limited. This study has been carried out with a view to analyse the use of magnesium alloy anode for the cathodic protection of steel embedded in concrete. Magnesium alloy anode, designed for three years life, was installed at the center of reinforced concrete slab, containing 3.5% sodium chloride with respect to weight of cement, for cathodic protection. Potential of the embedded steel and the current flowing between the anode and the steel were monitored, plotted and analyzed. Chloride concentration of concrete at different locations, for different timings, were also determined and analyzed. The magnesium anode was found to shift the potential of the steel to more negative potentials initially, at all distances and later towards less negative potentials. The chloride concentration was found to decrease at all the locations with increase in time. The mechanism of cathodic protection with the sacrificial anode could be correlated to the removal of corrosive ions such as chloride from the vicinity of steel.

Cathodic Protection of Steel in Concrete Using Conductive Polymer Overlays

Cathodic Protection of Steel in Concrete Using Conductive Polymer Overlays

Effectiveness of a conductive cementitious mortar anode for cathodic protection of steel in concrete

The paper reports a study on the behaviour of a cementitious conductive overlay anode used for cathodic protection (CP) of steel in concrete. The anode is made of nickel-coated carbon fibres in a cementitious mortar. Tests were carried out on concrete specimens with two layers of rebars that simulated reinforced concrete slabs. Anodic current densities in the range 10–100 mA/m2 with respect to the anode surface were imposed. Steel and anode potentials, as well as feeding voltage, were monitored. Four-hour decay and the distribution of current and potential were regularly measured. Galvanostatic polarisation tests were also carried out on the anode material immersed in saturated calcium hydroxide solutions. The maximum anode current output was evaluated. The effectiveness of patch repair of the anode, on areas damaged by excessive current output, is also discussed.

Non‐destructive determination of the sheet resistance of conductive coating anodes on concrete

Conductive coatings form the basis of a common anode system used in the cathodic protection of steel in concrete. One of the properties required by such a coating is a low sheet resistance (square resistance). This, together with the protection current density and anode connection geometry, determines the uniformity of the current distribution over the concrete surface. It is shown that the sheet resistance may be determined using a non‐destructive test employing a collinear four‐probe array. When a current (I), passed between the outer probes of an equally spaced four‐probe array, induces a voltage difference (δV) between the inner probes, the sheet resistance is given by (pgr;/ln2)x(dgr;V/I). The validity of the measured values may be assessed by the absence of any sensitivity to probe orientation and spacing. This technique may be used in the assessment of the quality of installed conductive coating anodes. The sheet resistance will depend on factors such as the thickness and age of the installed coating.

Chloride Ion Barrier Properties of Small Electric Fields in the Protection of Steel in Concrete

Abstract Analysis of the Nernst-Plank relation suggested that a relatively small voltage drop would maintain a significant chloride concentration difference across an ideal electrolyte. This effect was used as the basis for a possible criterion for the protection of steel in concrete in which the chloride concentration at the steel is maintained at a level below that necessary to cause passive film breakdown. The applicability of ideal solution theory to the electrolyte in a porous cement matrix was investigated by driving chloride ions against a concentration gradient across a cement mortar disc using a small applied potential difference. Results indicated the potential difference was an effective barrier to chloride ions and that the theory presented can be used in the design of an active chloride barrier. This protective effect can be monitored by determining the voltage drop through the concrete between an installed anode and the protected steel. However, caution should be exercised when dealing with ...

Cathodic protection of steel in concrete

Cathodic protection of reinforced concrete has been developed by a combination of trial and error, fundamental research, applied research and transfer of technology from related fields. These developments have been underway for 35 years and have been progressed by civil engineers, concrete technologists, corrosion scientists and cathodic protection engineers. In the past 6 years in the U.K. the investment in repairs to reinforced concrete structures incorporating cathodic protection has grown from a minimal £100,000 p.a. to some £20 million p.a. This paper reviews the developments in cathodic protection of reinforced concrete during the last 35 years with particular emphasis on developments during the last decade. The critical areas of this multi-discipline technology in respect of system performance and future development are anode systems, anode overlays and assessment of cathodic protection performance. These critical areas are addressed in detail and some requirements for future work are highlighted.

Cathodic protection of steel in concrete

Cathodic protection of steel in concrete