Half-cell Potential Measurements Research Articles

IBEM analyses on half-cell potential measurement for NDE of rebar corrosion

Corrosion of Reinforcement (rebar) is nondestructively estimated by the half-cell potential measurement. As is the case with other nondestructive testings (NDT), understanding of the underlying principles should be clarified in order to obtain meaningful results. Therefore, the measurement of potentials in concrete is analytically investigated. The effect of internal defects on the potentials measured is clarified numerically by the boundary element method (BEM). Thus, a simplified inversion by BEM is applied to convert the potentials on concrete surface to those on rebars, taking into account the concrete resistivity. Because the potentials measured on concrete surface are so sensitive to moisture content, concrete resistivity and surface condition, an inverse procedure to convert the potentials on concrete surface into those on rebars is developed on the basis of BEM. It is found that ASTM criterion is practically applicable to estimate corrosion from the potential values converted. In experiments, an applicability of the procedure is examined by accelerated corrosion tests of reinforced concrete (RC) slabs. For practical use, the procedure is developed where results of IBEM are visualized by VRML (Virtual Reality modeling Language) in three-dimensional space.

Potential and Current Flow of Double Steel Bars in Concrete by 2-D BEM

This study performs the numerical analysis of electric potentials and currents in reinforced concrete to achieve the nondestructive evaluation of corrosion using a half-cell potential measurement and polarization resistance method. Electric fields around single and double reinforcing steel bars were analyzed using a 2-D Boundary Element Method (BEM). In the half-cell potential measurement, the potential distribution in double reinforcing steel bars in concrete was represented as a singular shape rather than a circle shape. It means that the potential value inside concrete and current ratio in rebar are closely related to the size and the number of rebars. In the polarization resistance method, the polarized area of rebar is associated with the current density and current ratio.

Development of an Index for Concrete Bridge Deck Management in Utah

The purpose of this research was to develop a new index for concrete bridge deck management in Utah. Data were collected in the summer of 2005 from 15 concrete bridge decks in Salt Lake City. Decks ranged from 2 to 21 years in age and were all constructed with epoxy-coated rebar. Data collected from visual inspection, sounding, Schmidt hammer testing, half-cell potential testing, and chloride concentration testing were analyzed with statistics, and age, cover, and half-cell potential were ultimately selected for inclusion in a new Utah Bridge Deck Index (UBDI), which was structured around a deduct system using a 100-point scale. Coefficients were selected primarily on the basis of the judgment of the researchers and the Utah Department of Transportation (UDOT) personnel involved in the research. Also, threshold values for maintenance, rehabilitation, and replacement (MR&R) options were specified to be the same as those associated with standard sufficiency ratings. The UBDI and corresponding MR&R recommendation were then provided for each of the tested bridge decks. In addition, consideration of the possibility of treatment applications led to required adjustments in the UBDI calculation; the treatment options that were considered include an epoxy seal, a high-performance concrete overlay, and an asphalt membrane overlay. Four case scenarios were developed to demonstrate the response of the revised UBDI equation to these treatments. Finally, as aids for Utah DOT personnel implementing this research, charts were created to facilitate rapid determination of the required number of half-cell potential and cover measurements for different levels of reliability and tolerance.

Evaluation of corrosion activity in FRP repaired RC beams

Abstract This paper presents the results of an experimental study to evaluate the corrosion activity in reinforced concrete beams repaired with fibre reinforced polymer (FRP) sheets. Ten beam specimens (152 × 254 × 3200 mm) were constructed. One specimen was neither strengthened nor corroded to serve as a reference. Three specimens were corroded and not repaired. The remaining six beams were corroded and repaired with FRP sheets. The FRP sheets were applied after the main reinforcing bars were corroded to a 5.5% mass loss. Following the FRP repair, some specimens were subjected to further corrosion to investigate their post-repair performance. The corrosion activity was evaluated using non-destructive and destructive techniques. The non-destructive techniques included half-cell potential measurements. The destructive techniques included evaluation of the mass loss of the main reinforcing bars. The experimental results showed that the corrosion potential decreased with the progress of corrosion, and the FRP repair caused a higher rate of decrease in the corrosion potential with time than that observed when FRP was not provided. Results showed that mass loss of the main reinforcing bars due to corrosion was reduced by up to 16% because of FRP repair.

Effect of initial curing on chloride ingress and corrosion resistance characteristics of concretes made with plain and blended cements

This paper reports the results of an experimental study conducted to evaluate the effect of initial curing conditions on the chloride ingress characteristics of concretes made with plain and four different blended cements. In addition, the corrosive behavior of steel bars embedded in plain and blended cement concretes were studied through half-cell potential measurements. A total of ten different concrete mixtures having water–cement (w/c) ratios of 0.65 and 0.45 were cast and tested. Test specimens were subjected to three different initial curing conditions, namely uncontrolled, controlled, and wet before exposure to high chloride environment. The research variables included cement type (i.e., plain and blended cements), w/c ratio, and initial curing condition. The results indicated that the initial curing condition had pronounced effects on the related properties: in particular, the most prominent effects were observed on blended cement concretes, which performed extremely well when initially cured in wet conditions. Inadequate or poor initial curing practice resulted in remarkably lower chloride penetration resistance for both plain and especially blended cement concretes.

Electro-chemical chloride extraction: Influence of C 3A of the cement on treatment efficiency

The aim of this study was to clarify whether the C 3A content of cement had a significant effect on electrochemical chloride extraction (ECE) treatment efficiency. It is known that a higher C 3A content in a cement gives it superior chloride complexing ability resulting in the formation of an “insoluble” calcium chloro aluminate compound. ECE was applied using cylindrical specimens made from concrete containing two levels of C 3A (4.3% and 9.05%). Specimens were 5 cm in diameter and 10 cm in height. Steel was placed in the axial direction with an embedded length of 7 cm. These specimens were immersed in an NaCl solution and dried in a stream of air at 40 °C for 10 months. The corrosion was monitored by half-cell potential and polarization resistance measurements. After steel depassivation, ECE was applied for 20, 30, 40 and 50 days using a constant current density of 1 A/m 2 of steel. At the end of the treatment, the specimens were maintained at 20 °C and 70% RH in order to observe the evolution of the steel (electrochemical measurements). The results show that, after 30 days of treatment, the chloride content remained constant in the specimen. This was probably due to OH − ion formation on the steel. The OH − ions “contribute” to the current transport, decreasing the ECE efficiency. Concerning the C 3A content, ECE efficiency was slightly affected by C 3A because only a part of the bound chloride ions was released. From the point of view of corrosion, half-cell potential showed a shift in the positive direction, indicating little corrosion activity at 20 °C and 70% RH. However, polarization resistance measurements showed that 2 months post treatment corrosion rates were significant, although the corrosion rate decreased from 6 μA/cm 2 to 2.5 μA/cm 2.

Corrosion damage diagnosis of a reinforced concrete beam after 40 years natural exposure in marine environment

A detailed investigation of the chloride induced corrosion damage was performed on a 40 years old reinforced concrete beam exposed in marine environment. Visual observations, electrochemical measurements, carbonation depth, total chloride content were carried out. Half-cell potential measurements were used to locate corrosion areas. It appeared that the interpretation based on gradient of the potential was in good concordance with real state of damage. Complementary destructive methods are applied to observe the real corrosion state of steel rebars and characterize the corrosion products and the steel/concrete interface (optical and electronical microscopy tools (XRD, SEM, EDS and μ-Raman). All these data indicate that on the beam, one may distinguish two types of areas: “high-corrosion zones” and “low-corrosion zones.” Given the fact that the “high corrosion zones” were found to be close to corrosion induced cracks and that they have a different morphology, this contribution concludes that the position of these areas did not shift in time.

Monitoring the corrosion and remediation of reinforced concrete on-site: An alternative approach

Difficulties associated with the interpretation of site data collected over long periods of time from commonly used electrochemical corrosion monitoring techniques often make it difficult to assess the corrosion of reinforcing steel. An alternative approach for the interpretation of data is proposed, based on a model of the quality of passive film upon the steel surface. This model leads to a representation of the corrosion state by means of the relationship, over a long period of time, of the corrosion potential and the logarithm of the Linear Polarization Resistance, since both are functions inter alia of corrosion rate. It is shown that for the reinforced concrete panels tested, data points representing this relationship closely fitted a family of results; allowing the development of a “monitoring control diagram”, MCD. The MCD reveals that for a fixed geometry and experimental conditions, a relationship between the corrosion potential and polarization resistance of steel exists, facilitating a useful monitoring tool for assessment of both the corrosion and remediation of reinforced concrete structures. Particular emphasis is placed on the latter in this work. Monitoring the corrosion of steel embedded within concrete presents certain challenges, especially in terms of physical inspections. On-site electrochemical techniques that have been developed to monitor corrosion processes that may be occurring at the reinforcement surface, but of which there is as yet no evidence on the concrete surface, include: half cell potential measurements and linear polarization resistance measurements [1]. Such techniques are in good relation to the technical and financial scope of those conducting routine nondestructive testing. Up to the present, measuring the corrosion potential, E corr , of reinforcing steel is the commonest of the corrosion monitoring methods available [2], and is widely used in practice as an indication of the possible corrosion risk. Corrosion potential monitoring is outlined in ASTM C876 [3], in which the value of E corr is only claimed to indicate the relative risk of corrosion, with is no provision of quantitative information regarding corrosion rates. The standard suggests that passivity of the reinforcement may be lost at potentials more negative than � 150 mV (Cu/CuSO4) [3]. In the LPR technique (originally developed for metals in solution in the late 1950’s [4]), the potential of the steel is scanned over a small range in the vicinity of the corrosion (open-circuit) potential. As the current densities and potential shifts associated with the technique are small, it was considered in the original derivation of the theory that mass transport effects could be neglected. The slope of the polarization curve (viz. the potential change divided by the applied current) at the point at which the applied current equals zero is defined as RP, the Polarization Resistance, and is considered a measure of the opposition to metallic dissolution. Each of these techniques provides some information as to what is going on within the concrete, but none give the complete story [5, 6]. In particular the changes in the environment that are an inevitable feature of site measurements introduce random variations into the data that can often mask underlying fundamental changes in the corrosion process [7 – 9]. As opposed to the presentation of alternative techniques to replace E corr and LPR monitoring, this paper attempts to introduce an approach to analyzing data from such techniques; which aims to lead to more meaningful conclusions. The paper will illustrate this technique by using it in the context of ranking different corrosion remediation techniques.

Numerical simulation of potential distribution due to the corrosion of reinforcement in concrete structures

Corrosion of the reinforcement is one of the causes of reducing service-life of concrete structures. The methodologies used for making a decision on the repair or the replacement of damaged elements require in situ measurements for locating corroding areas. This paper is focussed on the results of the application of half-cell potential mapping for locating corroding areas on reinforced concrete pipeline and on six concrete columns. For reinforced concrete pipelines the validity of the half-cell potential measurements was confirmed by using finite-element calculations based on the distribution of the electrical field in soil. For the reinforced concrete columns, it was observed that the value of the half-cell potential can be inaccurate for locating corroding zones, when steel-concrete interface is cracked or when concrete cover is delaminated due to the expansion of corrosion products. This means that highly corroding areas are not always detected by this method. The occurrence of cracking and delamination in reinforced concrete structures was also studied by using a finite-element approach. It is shown that the absolute values of potential of steel in concrete depend on the delamination of concrete cover. So, the value of half cell potential should not be used as an indicator of corrosion. On the contrary, the potential gradient is a good indicator for locating corroding reinforcement in crack-free concrete surface. Some additional finite-element calculations were carried out to study the influence of concrete conductivity, cover thickness and delamination size on the size of concrete surface influenced by corrosion. So, this size increases with concrete cover thickness.

Field Evaluation of Marine Structures Containing Calcium Nitrite

A field study of corrosion of reinforcing bars in existing concrete pier structures is presented in this paper. The objective of the research was to evaluate the effectiveness of calcium nitrite for combating corrosion in marine structures. Five sites were selected for field evaluation of reinforcement corrosion in cooperation with the Harbors Division of the Hawaii Department of Transportation. The concrete for each of these sites included a calcium nitrite-based admixture as a corrosion inhibitor. Each site was tested for permeability, chloride ion concentration, half-cell potential, polarization resistance, and pH. Corrosion activity identified by half-cell potential measurements, polarization resistance measurements, and visual inspection of bars taken from cores indicated that high dosages of calcium nitrite, 19.8 to 22.3 L/m³, provided the steel with significantly greater protection than lower dosages, 12.4 L/m³. This occurred despite the fact that the sites with higher dosages were older and usually more permeable than the structures with lower dosages.

Effect of cement type on the corrosion of reinforcing steel bars exposed to acidic media using electrochemical techniques

The effect of different percentages of cement components (tricalcium aluminate C 3A) on the corrosion of embedded reinforcing steel bars was studied in presence of 5% NaCl or 5% MgSO 4 solutions. Different electrochemical techniques namely; half-cell potential measurement, impressed voltage method and impressed current method were used. The C 3A in cement reduced greatly the corrosion of steel bars embedded in concrete subjected to chloride or sulphate solutions. In chloride solution, as the percent of C 3A increased in cement from 2% to 10% the steel corrosion decreased proportionally. The rate of corrosion in 5% MgSO 4 solution was decreased as the percent of C 3A increased from 2% to 6%. From 6% to 10% the steel corrosion rate was rapidly accelerated. In general the presence of chloride and sulphate solutions in surrounding media reduced the destructive effect of sulphate ions on embedded steel bars.

Chloride Permeability and Corrosion Risk of High-Volume Fly Ash Concrete with Mid-Range Water Reducer

This study investigated the effect of local high-volume fly ash (HVFA) incorporating a mid-range water reducer on compressive strength of concrete and on chloride penetration and steel corrosion under tropical climate conditions. The results of electrically accelerated corrosion tests were compared with normal tests. Half-cell potential measurements and visual examination indicated the effectiveness of the corrosion reduction, independent of compressive strengths. A mid-range water reducer improved the 28-day strength by 50 to 75%, compared with 8 to 36% of concrete with 0 to 35% replacement. It also yielded lower chloride permeability and corrosion risk. HVFA concrete with a replacement of 50 to 65% was ranked at greater than 90% probability of no steel corrosion, and the corrosion rank improved from a severe-moderate level to slight or no corrosion at all. Fly ash content, water reducer, and water-binder ratio (w/b), respectively, were three parameters that influenced corrosion risk, while w/b was the most important factor for normal concrete.

Monitoring corrosion protection provided by fibre reinforced composites

A laboratory research programme was initiated to complement a field investigation in which composite materials were being used to wrap 12 corrosion damaged bridges in Texas. The programme, which started in 1997 and was sponsored by the Texas Department of Transportation, included more than 60 laboratory specimens that were designed to simulate bridge bents and columns. The primary objective was to determine whether composite wrapping could be used as a means of rehabilitating corrosion damaged structures. Since that time, the laboratory specimens have been subjected to intermittent exposure to saltwater conditions. They have been monitored using corrosion (half-cell) potential measurements that indicate the probability of corrosion activity. In addition, corrosion rate measurements have been determined on some of the specimens after exposure. Selected specimens have been removed from testing and subjected to thorough post exposure examination on a regular basis. The focus has been on the difference in the behaviour of the wrapped and unwrapped specimens. The composite systems used included a vinyl ester resin and two epoxy resins in combination with a selected fabric containing glass fibres. The laboratory specimens have been exposed to saltwater for more than four years. This paper represents a summary of some of the most significant findings during that time, as well as a comparison of those results with some of the results obtained in the field investigation.

The influence of cement type and admixture on life span of reinforced concrete utility poles subjected to the high salinity environment of Northeastern Brazil, studied by corrosion potential testing

Reinforced concrete structures installed in coastal zones have constantly been threatened by environmental damaging elements. The chloride ion is known as one of the most aggressive of these elements, causing, among other damages, corrosion of the steel reinforcement and then degradation of the concrete matrix. The goal of this work was to determine the influence of cement type on the resistance and durability of reinforced concrete samples with 25 mm cover thickness, when submitted to aging in a 3.4% sodium chloride aqueous solution and in a high salinity marine environment. Reinforced concrete light poles were cast following the same batching procedures, and after the curing period, they were exposed to atmosphere in a corrosion station near Aracaju, Sergipe State, Northeastern Brazil's coast. Two concrete mixtures were made using CPII-F 32 (filler-modified Portland cement): a mix with no admixture and a mix with addition of 8% silica fume swapping fine aggregates. Another mixture was batched with CPV-ARI RS (high-early-strength Portland cement, with sulfur resistance). All the three mixtures were designed with cement content of about 350 kg/m³. The performance of the structures was evaluated from the results of physicochemical, mechanical and electrochemical testing, after over a year of natural aging. Corrosion potentials of the reinforced concrete samples and of the cast utility poles were measured in terms of the aging time at the natural environment and under chloride ion accelerated aging at laboratory. The half-cell potential measurements showed that the best results were obtained from the mixture containing CPII-F 32 cement and silica fume, followed by the concrete made with CPV-ARI RS cement. The mixture batched with CPII-F 32 cement without admixture presented the worst durability performance.

Analysis of half-cell potential measurement for corrosion of reinforced concrete

Non-destructive evaluation techniques by the half-cell potential measurement are applied to estimate the corrosion of reinforcing steel-bars in concrete slabs under cyclic wet and dry conditions. The three-dimensional boundary element method (BEM) is applied to study the potential distributions and current flows of rebar. Then, the inverse boundary element method (IBEM) is applied to experimental results to identify the corrosion states. The influence of a void on the potential distribution and current flow is also investigated. Results show that the half-cell potential measurement is marginally successful, compared with analytical results of potential distribution and current flow by BEM. It is demonstrated that results by IBEM analysis identify clearly corroded areas.

BEM ANALYSES ON HALF-CELL POTENTIAL MEASUREMENT AND CURRENT FLOW

Numerical analysis of electric potentials and currents inside reinforced concrete is performed to study nondestructive evaluation of corrosion by the half-cell potential measurement and polarization resistance method. Electric fields around reinforcing steels are analyzed by using the Boundary Element Method (BEM). 3-dimensional analysis is conducted to compare with 2-dimensional analysis. Distributions of potentials inside concrete and current flows around rebars are clarified three-dimensionally.

Half-cell potential measurements—Potential mapping on reinforced concrete structures

Half-cell potential measurements—Potential mapping on reinforced concrete structures

Recommendations of RILEM TC 154-EMC: Electrochemical techniques for measuring metallic corrosion Half-cell potential measurements - Potential mapping on reinforced concrete structures

Recommendations of RILEM TC 154-EMC: Electrochemical techniques for measuring metallic corrosion Half-cell potential measurements - Potential mapping on reinforced concrete structures

The effect of concrete surface treatments on electrical measurements of corrosion activity

One option to extend the life of concrete structures threatened by reinforcement corrosion is the timely application of surface treatments. It is obviously desirable that test methods be available to assess the effectiveness of such remedial work. Electrochemical measurements are widely used in concrete construction to assess the likelihood of corrosion. There is, however, little information on the ability of these methods to perform effectively once a protective treatment has been applied to the surface of the concrete and the project described here was, therefore, set up to determine whether non-destructive electrochemical measurement of corrosion activity in concrete can give reliable information when protective coatings are applied to the surface of the concrete. The results indicate half-cell potential measurements were not affected to a significant degree by the presence of a coating, but that appreciable errors could be introduced in polarisation measurements.

Indicators for inspection and maintenance planning of concrete structures

Based on an idea introduced by Benjamin and Cornell (1970. Probability, statistics and decision for civil engineers. New York: McGaw Hill) and previous works by the authors it is demonstrated how condition indicators may be formulated for the general purpose of quality control and for assessment and inspection planning in particular. The formulation facilitates quality control based on sampling of indirect information about the condition of the considered components. This allows for a Bayesian formulation of the indicators whereby the experience and expertise of the inspection personnel may be fully utilized and consistently updated as frequentistic information is collected. The approach is illustrated on an example considering a concrete structure subject to corrosion. It is shown how half-cell potential measurements may be utilized to update the probability of excessive repair after 50 years. Furthermore in the same example it is shown how the concept of condition indicators might be applied to develop a cost optimal maintenance strategy composed of preventive and corrective repair measures.