Chloride-contaminated Concrete Research Articles

Long-Term Performance of Fusion-Bonded Epoxy-Coated Steel Bars in Chloride-Contaminated Concrete

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Corrosion of Steel Reinforcement in Concrete Adjacent to Surface Repairs

Reinforced concrete may be damaged by chloride-induced corrosion of steel reinforcement, resulting in spalling and delamination as corrosion products accumulate. A surface repair entails removal of damaged concrete and its replacement with repair material. The resulting inhomogeneity between the repair material and remaining chloride-contaminated concrete, however, may produce active-passive corrosion macrocells that drive rapid anodic dissolution of the metal. This experimental study was conducted to characterize the geometry, current distribution, and controlling resistance of corrosion macrocells driven by differences in the electrochemical environment in repair material and contaminated concrete. Additional influences such as galvanic contact between the test reinforcement bar and remote cathode bars were also considered. The tests were based on ASTM G 109, with modifications to incorporate simulated repairs.

New method to measure the rapid chloride migration coefficient of chloride-contaminated concrete

The apparent chloride diffusion coefficient, D app, which is obtained by fitting chloride profiles as the result of time-consuming immersion tests can be substituted in a model on chloride ingress by the rapid chloride migration (RCM) coefficient of concrete, D RCM, which is determined under electrically accelerated conditions. Until now, it was not possible to measure D RCM of chloride-contaminated concrete, as already inherent chlorides interfere with the common colorimetric indicator used for penetration depth measurements. Furthermore, carbonation may also interfere with the penetration depth reading. To overcome these problems, the regular test has been modified by using iodide as penetrating ion and iodate–starch acetic acid as indicator. A strong linear relationship between the regular RCM test and the newly developed Rapid Iodide Migration (RIM) Test was found. Carbonated specimens can be tested using the RIM test without additional interference. Thus, the new method enables the quantification of the actual concrete quality sampled from existing structures during a condition assessment.

Macrocell Activity in Slightly Chloride-Contaminated Concrete Induced by Reinforcement Primers

Abstract Patch repair systems are usually composed of a primer (or paint) for the reinforcement, a bond bridge, and a repair mortar to restore the initial geometry. This system is said to induce an enhancement of the corrosion activity of the adjacent nonrepaired zones if they still contain a certain amount of chlorides. In the present paper, the action of the steel primers on the galvanic effect toward unrepaired zones was studied. Four protection mechanisms were selected: repassivation, inhibition, barrier, and cathodic protection. Small beams were fabricated with an embedded, continuous bar in the top part and a segmented one that enabled the monitoring of the corrosion potential and the corrosion rate of each segment when disconnected, and the macrocell or galvanic activity between segments in repaired interfaces and nonrepaired zones. The results after submitting the beams to different humidity conditions show that the primers were mainly effective in the first month after repair and sometimes they m...

Change of pore size in concrete due to electrochemical chloride extraction and possible implications for the migration of ions

Electrochemical chloride extraction (ECE) is used for the rehabilitation of chloride-contaminated concrete. Anions such as chloride and hydroxide are pushed away from the cathode (reinforcement), and cations such as sodium, potassium and calcium are attracted to the cathode. During ECE an increase of the concrete resistance can be observed. The results of a petrography study on ECE-treated concrete are presented in this paper. It also investigates the influence of pore size on ion migration using a concrete substitute model with known pore size. Findings showed that the pore size and pore size distribution of concrete are altered due to ECE. It is therefore suggested that concrete acts as active migration medium in the migration process by releasing ions into the pore solution. Moreover, small pores hinder the migration of ions, which may partially be responsible for changes in concrete resistance.

Galvanic Corrosion of Steel in Contact with Carbon-Polymer Composites. II: Experiments in Concrete

Studies were conducted to understand the galvanic interactions between CFRP and steel in chloride-contaminated concrete. CFRP-pultruded rod samples (6 mm in diameter), #3 deformed plain rebar (PR, uncoated), and #4 epoxy-coated reinforcing (ECR) steel bars were tested. After 350 days, potential measurements of CFRP and steel samples in chloride-contaminated concrete were −200 and −600 mV (versus CSE), respectively. These results confirm that chloride contamination in concrete could allow galvanic corrosion between CFRP and steel. The measured galvanic current densities were up to 0.7 and 100 μA/m2 for the CFRP-PR and CFRP-ECR couples, respectively, raising concerns about the degradation of both CFRP and steel. The results showed that PR steel was unaffected, as the corrosion rates estimated before and after the coupling with CFRP were similar. In contrast, coupling CFRP and ECR steel showed an increase of 10 times of the estimated corrosion rate, suggesting that galvanic interaction might affect the ECR s...

Evaluation of a composite corrosion-inhibiting admixture and its performance in concrete under macrocell corrosion conditions

The objective of this present investigation is to design a composite corrosion-inhibiting admixture system comprising of both mineral and chemical admixtures and to evaluate its performance in concrete under macrocell corrosion conditions. The newly designed corrosion-inhibiting admixture system performed very well in chloride-contaminated concrete. Steel embedded in ordinary Portland cement suffered severe corrosion. In concrete incorporating the designed admixture system, steel showed a 10-fold decrease in corrosion rate of steel embedded in concrete under accelerated macrocell corrosion conditions. The compressive strength of mortars was not affected by adding the designed admixture system.

Corrosion Products of Galvanized Rebars Embedded in Chloride-Contaminated Concrete

Abstract Iron corrosion products of steel reinforcement result in staining, cracking, and spalling of concrete structures. These effects of corrosion require costly repairs and maintenance during the useful life of the structures. To prevent corrosion of important infrastructure projects, galvanized reinforcing steel occasionally is used. The performance of galvanized steel in chloride-contaminated concrete is attributed to the corrosion product form: zinc oxide (ZnO), which is less voluminous than iron corrosion products. However, zinc corrosion products detected on galvanized reinforcement are rather controversial. Some authors identified another compound: zinc hydroxychloride (Zn5[OH]8Cl2·H2O). This product occupies more space than ZnO and can induce cracking of the cover concrete. Other authors found zinc hydroxychloride and zinc hydroxide (Zn[OH]2). In this work, ZnO and Zn5(OH)8Cl2·H2O were identified. Under some conditions (exposure time in aggressive environment and coating thickness) and after cracking of concrete cover, Zn(OH)2 also was found.

Effect of holidays and surface damage to FBEC on reinforcement corrosion

This study was conducted to evaluate the effect of holidays and damage to fusion bonded epoxy coating (FBEC) on reinforcement corrosion in chloride-contaminated concrete. The effect of these parameters on the corrosion of FBEC bars was compared with corrosion of mild steel by measuring the corrosion potentials and corrosion current density at regular intervals. The corrosion current density measurements indicated that the defect-free FBEC bars were in a passive condition in the concrete specimens with up to 2% chloride by weight of cement. The long-term maintenance-free performance was not assured in the concrete specimens with chloride concentration of 1% and above and made with FBEC bars having >1% surface damage or with 3 holidays per linear foot. The long-term performance of FBEC bars with up to two pinholes (ASTM A 775 limit) was satisfactory in the concrete specimens with up to 2% chlorides, by weight of cement. Furthermore, surface damage to FBE coating is more critical compared to holidays, from the point of view of corrosion of FBEC bars, in chloride-bearing concrete.

厳しい塩害環境下での鉄筋コンクリート構造物の耐久性に関する研究 : アクリルゴム系防水塗膜の効果

A field reinforced concrete structure with and without an acrylic rubber-based surface coating was built in Okinawa for this research project, and it has been exposed to severe marine environment for ten years. The test on this structure gives the following results : (1)In unprotected concrete, the penetration of chloride ions into concrete is very rapid, and the corrosion of reinforcing bars occurs in early stage. (2)The acrylic rubber-based surface coating acts as a complete barrier to the transport of chloride ions, water and oxygen, and prevents the corrosion of the bars in chloride-contaminated concrete.

The C1−/OH− ratio in chloride-contaminated concrete — a most important criterion

Chloride-contaminated concretes were produced either by admixing sodium chloride with original mixes or as a result of exposure to external sodium chloride solutions. Free chloride and hydroxyl ion concentrations in the pore solutions of the concretes were determined. It was found that the value of free chloride content by itself cannot provide a meaningful indication of the susceptibility of the reinforcement to chloride-initiated corrosion. The ratio of free chloride to hydroxyl ion concentrations in the pore solution and differentiation between admixed and externally applied chloride are found to be factors that must be known if indicative values to predict corrosion are sought. Charts giving safe regions of C1−/OH− values for various concretes are suggested. The use of a superplasticizer in concrete making was found to increase the concentration of free chloride and to raise the value of Cl−/OH− ratio in all the concretes tested. The use of fly ash was found beneficial in immobilizing the chloride ions in non-superplasticized concrete. However, in concrete made with a superplasticizer the inclusion of fly ash was found to cause a greater release of chloride ions into the pore solution.

Comparison of rates of general corrosion and maximum pitting penetration on concrete embedded steel reinforcement

Local attack of reinforcement is observed usually in chloride-contaminated concrete. When mechanical weakening of the concrete structure is affected by the bar section loss in the places where corrosion is intensified, the maximum penetration of the deepest pits happens to be a very relevant datum. In this work average corrosion values are compared with maximum pit depth values. Using natural corrosion tests and accelerated tests, it has been found that the maximum penetration of localized attack on steel embedded in concrete containing chlorides is equivalent to about four to eight times the average general penetration.

An investigation into the mechanisms of protection afforded by a cathodic current and the implications for advances in the field of cathodic protection

The influence of a cathodic current on the corrosion behaviour of mild steel exposed to both dilute sodium nitrate solutions and chloride contaminated concrete has been examined. In both cases the formation of passive films was promoted by stimulating a cathodic reaction on the metal surface, the cathodic kinetics being under activation control in the near passive region. The sodium nitrate solution was not capable of supporting a passive film on its own and it is suggested that, in this environment, film formation is promoted by the production of inhibitors (hydroxyl ions, free radical intermediates and metal oxide intermediates) resulting from the cathodic reduction reaction. In chloride-contaminated concrete an additional effect is the removal of aggressive anions via the flow of negative ionic current away from the metal surface. These passivating effects of the cathodic current provide persistent protection and may be harnessed to develop intermittent cathodic protection for use in areas such as the tidal zone where an electrolyte is not always present. The improvement in the local environment at the steel surface may facilitate a reduction in the protection current density, a factor which may be used to reduce the risk of overprotection when cathodic protection is applied to prestressing steel. The use of potential depolarisation and current density related criteria may be more appropriate than the achievement of a predetermined absolute potential in cases where the purpose of the cathodic protection system is to induce passivation.

Performance of Black, Galvanized, and Epoxy-Coated Reinforcing Steels in Chloride-Contaminated Concrete

Abstract The corrosion performance of black steel, galvanized steel, and epoxy-coated steel in concrete was investigated. Samples were exposed to cyclic salt water wetting and drying or to a contin...

Chemical Treatment of Corroding Steel Reinforcement After Removal of Chloride-Contaminated Concrete

Abstract The increasing use of deicing salts on bridge decks has accelerated their deterioration due to chloride-induced corrosion of steel reinforcement, which causes cracking and spalling. One method being considered as a possible corrosion abatement measure is the removal of chloride-contaminated concrete followed by chemical treatment of the partially exposed rebar through ponding and/or placement of chemically treated mortar. Several commercial and experimental corrosion inhibitors were evaluated in order to determine the most effective corrosion treatment when applied in conjunction with removal of chloride-contaminated concrete. The performances of the inhibitors were evaluated in an accelerated test program. Based on post-treatment electrochemical measurements, calcium-nitrite-based corrosion inhibitor was most effective when applied as a ponding and when placed in backfilled mortar. Several other inhibitors were also sufficiently effective and were recommended for further evaluation in large-scal...

Investigations of reinforcement corrosion. 2. Electrochemical monitoring of steel in chloride-contaminated concrete

Corrosion rates of steel rods embedded in concrete specimens similar to those of Part 1 have been determined by linear polarization. For specimens exposed to external sources of chloride the probability of depassivation increased with the chloride: hydroxyl concentration in the pore solution, beyond a threshold ratio of approximately 3. Thereafter corrosion was subject to anodic control. Chlorides introduced as admixtures tended to promote corrosion at somewhat lower chloride: hydroxyl ratios. Rankings of the materials and exposure regimes studied in terms of their corrosion severity have been established, and problems in relating the behaviour of laboratory specimens to that of reinforced concrete structures are considered.

Investigations of reinforcement corrosion. 1. The pore electrolyte phase in chloride-contaminated concrete

A sampling procedure, which avoids the need for wet cutting, has been developed for determination of compositional profiles of the pore liquid phase within concrete exposed to chloride ingress. The technique has been used to assess the effects on various concrete specimens of exposure to different regimes of chloride penetration and to compare them with those of salt, introduced as a constituent of the mix materials. The implications regarding corrosion risk to embedded steel are provisionally evaluated in terms of the ratio of chloride to hydroxyl ion concentrations in the pore solution. The significance of this parameter is to be considered in Part 2.

The behaviour of galvanized steel in chloride-containing alkaline solutions-I. The influence of the cation

The behaviour of galvanized reinforced bars (rebars) in chloride-contaminated concrete is a very controversial matter not yet resolved. An extensive study of the behaviour of galvanized steel in alkaline solutions which simulate the aqueous phase present in concrete pores has been undertaken. This paper describes the modifications that the presence of chloride has on the corrosion behaviour of galvanized steel in alkaline solutions, as well as the influence of the accompanying cation. It was confirmed that the corrosion behaviour of galvanized steel in the presence of chlorides is controlled by the medium pH, which depends on the calcium or sodium salt which provides the chloride ions.

Evaluation of the efficiency of a repaired chloride-contaminated concrete

This report describes several tests that are being carried out on a viaduct near Madrid City, whose reinforcements have been seriously damaged by corrosion. These tests consist in measuring corrosion potentials and in a time soon to come, they will include the measurement of corrosion rates by means of the apparent Polarization Resistance. A methodology of laboratory tests to evaluate the protective capacity of the repairing system used towards the reinforcements is also included. Tests results have reported that the repairing materials employed do not fit the repassivating and protective function they should satisfy. Finally, it is also recalled to attention the real need in developing suitable test specifications able to provide a characterization of these repairing materials when they are going to be employed in structures damaged by corrosion in reinforcements.