ISO/DIS 18726.2:2026(en)

ISO TC 71/SC 7

Secretariat: KATS

Date:2025-12-20

Assessment, prevention, and repair for steel corrosion in reinforced concrete structures

© ISO 2026

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Contents

Foreword v

Introduction vi

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Basis of maintenance and repair for steel corrosion in concrete 3

4.1 General 4

4.2 Controlling steel corrosion 4

4.3 Procedure of maintenance and repair 4

4.4 Assessment 4

4.5 Repair for the purpose of prevention 4

4.6 Repair for the purpose of restoration 4

4.7 Combination of repairs 4

4.8 Competence of personnel 4

5 Maintenance plan 4

5.1 General 4

5.2 Maintenance category for steel corrosion 4

5.3 Formulation of maintenance plans 5

6 Assessment 5

6.1 General 5

6.2 Assessment plan for corrosion status 5

6.2.1 Preparation of assessment plan 5

6.2.2 Category of assessment 5

6.2.3 Level of assment 5

6.2.4 Assessment interval 5

6.3 Investigation 5

6.3.1 Steel corrosion 6

6.3.2 Concrete properties 6

6.3.3 Environments 7

6.4 Registration of condition 7

6.4.1 Determination for the onset of corrosion 7

6.4.2 Determination of corrosion risk 7

6.5 Evaluation and decision making 9

7 Repair 9

7.1 General 9

7.2 Planning and design 10

7.2.1 Strategy planning 10

7.2.2 Selection of repair 10

7.3 Execution 10

7.3.1 Concrete-surface treatment 11

7.3.2 Electrochemical treatment 10

7.3.3 Repair of cover concrete at steel corrosion 10

7.3.4 Repair of embedded steel at steel corrosion 10

7.3.5 Maintenace following completion of repair 10

8 Recording 14

Annex A (Assessment technique for steel corrosion) 15

Bibliography 17

Foreword

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This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-stressed concrete, Subcommittee SC 7, Maintenance and repair of concrete structures.

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Introduction

Corrosion of steel in concrete structures usually occurs in service, resulting from external sources such as chloride ions (i.e. destroying the passivation film of steel on its surface), a pH fall of concrete cover (i.e. carbonation and leaching-out of alkali ions such as Ca²⁺), a stray current, repetitive bending or other means. As long as sound steel is used with an appropriate process of concrete mixing, casting and curing, steel can be usually protected from corrosion. Once corrosion of steel is, however, initiated, it is then rapidly developed to form a crack in the vicinity of the steel embedded, which can be further produced to the outer surface concrete, leading to structural failure.

Despite the importance of the issue on steel corrosion in concrete structures, there have not been international standards covering maintenance of concrete structures particularly subjected to corrosion of embedded steel to date. In particular, assessment, prevention and repair techniques are mutually inter-related, and thus a clear-cut definition is important to have in an international organization.

To encompass the maintenance and repair of concrete structure suffered from corrosion of steel, the assessment and repair are included in this document, with respect to the techniques of corrosion measurement, repair for the purpose of prevention and that for restoration. Simultaneously, the risk of corrosion is determined to provide information on external environments that instigate corrosion of steel in concrete structures, while the prevention techniques are categorised.

Assessment, prevention and repair for corrosion in reinforced concrete structures

While the ISO 16311 series present the framework, general principles and standard methodologies for maintenance and repair of concrete structures, this document gives particular issues for those with corrosion of steel embedded in reinforced concrete structures.

Assessment deals with steel and concrete cover concerned with steel corrosion. Determination of the onset of corrosion is also included for further action, such as repair.

Prevention deals with all external treatments to mitigate or to remove the corrosion risk in concrete structures. Preventive measures mainly consist of concrete-surface treatment and electrochemical treatment, which can be used in the design and execution stages for repair of concrete structure are dealt with in this document.

Repair deals with strategy for repair of concrete structures subjected to steel corrosion. This document also considers recovery of steel and concrete cover for service life extension.

This document deals with carbon steel reinforcement in reinforced concrete structures. This document does not consider premature corrosion of steel before casting of concrete, such as steel in handling.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 16311‑1, Maintenance and repair of concrete structures — Part 1: General principles

ISO 16311‑2, Maintenance and repair of concrete structures — Part 2: Assessment of existing concrete structures

ISO 16311‑3, Maintenance and repair of concrete structures — Part 3: Design of repairs

ISO 16311‑4, Maintenance and repair of concrete structures — Part 4: Execution of repairs

ISO 22040, Life cycle management of concrete structures

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

3.1

assessment

set of activities performed in order to verify the reliability of an existing structure focusing on the corrosion of embedded steel and its consequences for performance degradation

3.2

carbonation

phenomenon in which the alkalinity of concrete is reduced to neutral level about 8,0-10,0 in the pH, usually arising from the chemical reaction between carbon dioxide, water molecules and precipitated Ca(OH)₂ in cement matrix to form CaCO₃

3.3

chemical corrosion inhibitor

chemical admixture to prevent, or at least mitigate steel corrosion, which can be used in solution or in powder to enhance the resistance of steel against corrosion

3.4

corrosion of steel in concrete

all reaction of loss of electrons on the steel surface and thus oxidation of steel in concrete structures, of which the main causes include chloride ions from an external environment, such as seawater, deicer, and carbonation (3.2)

3.5

electrochemical treatment

electrochemical application to concrete structures by completing electric circuit through steel and external cathode to modify chemistry at the steel-concrete interface, of which the main purpose includes mitigation of the corrosion of steel in concrete structures, encompassing cathodic protection, electrochemical chloride extraction and realkalisation

3.6

patching

overlay/underlay with non-corrosive cementitious materials in the form of mortar or paste at the indentation of concrete cover after removing the rust on the steel surface

3.7

prevention

remedial action to prevent or slow down the further deterioration of a structure or its component and to reduce the possibility of damage to the user or any third party, inhibiting the progress of deterioration, and proactively preventing deterioration caused by the corrosion of embedded steel; focusing on external installation for preventive measures equipped out of concrete structures with no relation to design of concrete structure

3.8

repair

restoration of a structure or its components to an acceptable condition by the renewal or replacement of worn, damaged, or deteriorated components under the effect of corrosion of embedded steel including prevention and protection

Note 1 to entry: Repair is adopted to restore structural performance and to mitigate safety risks up to the initially required design level and to achieve the intended service life.

3.9

service life

actual period during which a structure meets the prescribed performance requirements

[SOURCE: ISO 16311-1]

Note 1 to entry: In this document, the service life for reinforced concrete structures under the probability of corrosion is defined as the time for the onset of corrosion in the steel reinforcement. Other definitions for the service life of concrete structures do exist, e.g. time to cracking at the steel/concrete interface, time to surface cracking, or time to concrete cover spalling.

A reinforced concrete structure under the risk of steel corrosion shall retain the performance requirements for its service life by providing necessary maintenance and repair activities, such that its performance is always above the required level with adequate reliability under an appropriate maintenance plan. In this procedure, the service life is regarded as the time to the onset of corrosion, which shall be regularly measured and monitored in the maintenance activity. A qualified personnel in the area of steel corrosion in concrete shall develop a proper maintenance plan that could permit a reinforced concrete structure under the risk of steel corrosion to retain its performance requirements.

For corrosion of steel in concrete structures to be under control, the following are the general bases:

— a proper maintenance plan with respect to steel corrosion in concrete structures shall be formulated in consideration of performance requirements as well as sustainability specified in ISO 22040;

— assessment of status of steel corrosion in concrete structures shall be regularly made with appropriate ways;

— preventive measures shall be preliminarily adopted;

— repair techniques shall be applied to concrete structures once corrosion of steel is confirmed;

— combined methods for preventive measure and repair should be made.

The general flow of maintenance procedure for steel corrosion in concrete structures complies with ISO 16311-1. The overall activities for steel corrosion in concrete structures shall encompass the maintenance plan and assessment, followed by remedial action such as prevention and repair if required. The preventive measures should be preliminarily adopted in accordance with the maintenance plan.

Once the maintenance plan is made for concrete structures under the risk of steel corrosion, the assessment shall be made for steel corrosion, concrete and environment. When the symptom of the corrosion initiation is taken, the remedial action for repair shall be adopted in accordance with the maintenance plan.

Results of these activities shall be recorded with an easily accessible format.

Assessment consists of investigation of corrosion and subsequent evaluation of structural performance of structures suffered from steel corrosion.

Investigation of the corrosion shall be made in regular intervals with appropriate measurement techniques to identify the onset of corrosion or the probability of corrosion. Corrosion should be regularly monitored to alert the risk of corrosion in real time for highly important and risky concrete structures.

The evaluation of corrosion shall take into account the external environment, including temperature, moisture condition, CO₂ and chloride concentrations. CO₂ and chloride concentration should be meausred in an external environment and in concrete, because they are the main causes of steel corrosion in concrete. Temperature and moisture condition in concrete structures can affect the reactivity of steel corrosion.

To prevent corrosion of steel in concrete structures, either or both of the following prevention techniques should be preliminarily adopted with techniques given in Clause 7.

— concrete surface treatment (and impregnation);

— electrochemical treatment.

The inhibition effect of the adopted prevention technique shall be confirmed before its application. The confirmation information shall be used in the prediction of the service life of the concrete structure.

Note Concrete Surface treatment (impregnation) and electrochemical treatment are used to apart steel from corrosive resources , and to inhibit steel corrosion. To achieve prevention of steel corrosion in concrete structures, sources of corrosive ions, such as chloride ions and CO₂ shall be prevented from percolating into concrete or at least to the depth of the steel within service life. Inhibitive nature of steel is achieved by electrochemical treatment then to be preventive.

Repair shall be adopted once corrosion of steel in concrete structures is confirmed with techniques given in Clause 7. To repair concrete structures subjected to corrosion of steel, corrosive sourced should be eliminated in the process of repair. Corroded steel should also be repaired; rust on the steel should be eliminated with no structural impact. Alternatively, section repair or patch repair should be performed with replacing severely corroded steel with new one depending on the status of steel corrosion.

To enhance the effect of corrosion inhibition of steel, one or more techniques should be used for prevention before the onset of corrosion and repair after corrosion. Economic cost for repair, possible source of steel corrosion, type of concrete structure, environmental conditions, and importance of the structure shall be considered.

All activities of maintenance and repair shall be carried out by a team of qualified persons having the adequate knowledge and experiences of steel corrosion in concrete.

For accomplishing overall maintenance activities, an adequate maintenance plan for steel corrosion in concrete structures shall be formulated taking into account the maintenance category selected provisionally in accordance with 5.2, design service life, predicted time to the onset of steel corrosion, life-cycle cost, and other considerations particular to the structure. The maintenance plan shall follow the basic life cycle management scenario specified in ISO 22040. Sustainability shall be well considered to draw up the maintenance plan.

A suitable maintenance category for steel corrosion in concrete structures shall be selected to carry out the maintenance work as effectively as possible in consideration of such factors as the importance of the structure, design service life, predicted time to the onset of steel corrosion, safety risk concerns, environmental conditions, ease of maintenance, and cost. The maintenance categories shall be classified as preventive maintenance, corrective maintenance, and observational maintenance.

A provisional maintenance category shall be selected to formulate the maintenance plan for steel corrosion in concrete structures. When the results of initial assessment prescribed suggest that the provisional maintenance category is not suitable, it shall be revised. Consequently, the maintenance plan shall be determined in accordance with the finally selected maintenance category.

The status of steel corrosion in concrete structures shall be regularly, or imminently if necessary, assessed by appropriate means, depending on types of concrete structures, possible source of corrosion and a given environment such as atmospheric condition, relative humidity and temperature.

At assessment, the status of steel shall be measured in terms of corrosion and simultaneously physical and chemical properties of concrete related to steel corrosion, such as moisture content, constituent components and so on. The pH value of concrete cover and chloride contamination shall be monitored in order to substantially determine the probability of steel corrosion.

Once a symptom of steel corrosion is noticed, a future action shall be determined in terms of repair. Otherwise, a further assessment shall be performed to achieve more quantitative information on the status of steel corrosion in concrete structures. The entire process of assessment for steel corrosion in concrete structures shall accordingly conform with ISO 16311-2.

To identify critical characteristics of the steel corrosion in concrete structures, the expected condition of the structure with respect to steel, concrete and environment during its remaining service life should be appropriately specified prior to the assessment planning. The preparation of an assessment plan, therefore, should begin with the documentation of relevant performance criteria such that areas of concern that would compromise the structure meeting or exceeding its design service life to the onset of corrosion are identified.

Assessment performed in maintenance activities for concrete structures under the risk of steel corrosion throughout its service life shall be categorised suitably on the basis of the timing of assessment and the type of information desired as follows:

In general, the assessment is classified in the following three categories:

— initial assessment: an assessment carried out for evaluating the initial condition of steel corrosion before initiating into routine/regular maintenance activities;

— periodic assessment: assessment of steel corrosion with respect to steel, concrete and environment carried out routinely or regularly at certain intervals prescribed in the maintenance plan;

— extraordinary assessment: assessment carried out after the onset of corrosion or unexpected severe corrosion.

When some visual signs of steel corrosion are observed such as rust stain on the concrete surface through cracking or when there is a suspicion that steel corrosion is ongoing, the assessment should be carried out spontaneously in spite of the routine or regular interval.

An appropriate assessment level for steel corrosion in concrete structures shall be selected depending upon the purpose and scope of the category of assessment:

In general, two levels of assessment are defined as follows:

— Preliminary level: assessment to collect the basic information on steel corrosion by using simple investigation methods complied with a maintenance plan, such as a visual inspection, half-cell potential measurement and simple non-destructive test;

— Detailed level: assessment to collect detailed and specific information regarding steel corrosion and contamination of concrete by corrosive ions and molecules.

The detailed level assessment should be used when the assessment in the preliminary level is insufficient for identifying the corrosion causes, corrosion risk, the time to the onset of corrosion or corrosion degree.

Depending on the importance of concrete structures and equipment used for measuring corrosion status, the values for steel corrosion shall be continually measured and monitored. However, the assessment shall be performed in a given interval, for example every month, every 6 months or every year.

The time interval between assessments shall be determined by engineers and contractors, considering the importance of the concrete structure, budget for maintenance, risk of steel corrosion and given environment.

Non-destructive methods should be used to assess the status of steel corrosion in concrete structures, some of which are as follows:

— visual inspection;

— half-cell potential measurement and mapping;

— galvanic current monitoring;

— linear polarisation for corrosion rate;

— alternating current (AC) impedance for corrosion rate.

Note The details of the assessment techniques are further given in Annex A for the assessment of steel corrosion in concrete.

As corrosion of steel in concrete structures occurs, mainly resulting from chloride ions or a pH fall in concrete cover, concrete properties in terms of chloride profile and a pH profile (i.e. whether or not concrete is carbonated) should be measured. However, the investigation techniques used for this purpose are destructive ones and thus, their application may be restricted. Otherwise, appropriate restoration should be accompanied after sampling for these assessments of concrete properties.

Also, since concrete properties, such as moisture level, porosity, hydration degree and cracking are key factors to assess steel corrosion, these values should be considered in the list of assessment if necessary:

— Chloride profile: To achieve chloride profile, either a concrete core can be obtained, or powder samples can be obtained by grinding from the surface with increasing depths. Once sample is obtained, chloride concentration at each depth shall be to achieve a chloride profile, of which information shall be used to predict the risk of steel corrosion. To determine the rate of chloride transport in terms of diffusion, Fick’s second law can be used as follows:

(1)

where,

C(x,t) is concentration of chloride ions;

C_S is concentration of chloride ions on surface of concrete;

x is depth of concrete;

D is diffusion coefficient;

t is time;

e_f is error function.

— pH profile: To achieve a pH profile, an identical method to chloride profile shall be used for sampling. Then, the pH value at each depth shall be determined to achieve a pH profile. Otherwise, a concrete core should be used to determine whether carbonation reaches to the depth of the steel. Colour change shall determine the carbonation depth by spraying phenolphthalein solution on the cross-section of a concrete core.

— Other properties: Moisture content, porosity, hydration degree, concrete resistivity and cracking influence the corrosion of steel. Thus, these values should be included in the assessment. These values are often inter-related.

To reflect external exposed environments in the corrosion process, all environmental factors, such as temperature, relative humidity, wind and atmospheric concentrations should be quantified.

In particular, since the concentration of chloride in seawater, tidal condition and annual amount of deicer on motorway are key factors to chloride-induced corrosion of steel, environmental assessment shall be included, if necessary. The environmental assessment shall be simultaneously included in the assessment of carbonation-induced corrosion to provide informative background.

Note As for carbonation-induced corrosion, the concentration of carbon dioxide in air and relative humidity are very influential to the rate of carbonation of concrete cover.

The service life of the concrete structure under corrosion risk shall be defined as the time for the steel to reach the onset of corrosion. Depending on techniques, the values for the onset of corrosion can be derived from qualitative or quantitative methods, as given in Table 1.

For visual inspection, the time to rust stain formation shall be regarded as the time of the onset of corrosion, while -350 mV vs CSE (copper/copper sulfate electrode) shall be the threshold voltage for indicating the corrosion initiation at 90 % probability. By galvanic monitoring, the corrosion initiation can be recognised by a sharp increase about 2-3 order as seen in Figure A.1 in Annex; the ladder cell system, consisting of six mild steel and a noble metal galvanically connected through a resistor to alert the corrosion of the steel with incremental depth should be used to monitor and predict the corrosion risk with time.

Note As for polarisation and AC impedance techniques, no national standard or guidelines provide any value for corrosion initiation, whilst some guided values have been provided in research.

Note The corrosion current at corrosion initiation is regarded as 1-2 mA/m² in concrete/mortar conditions, when the corrosion of steel is measured by polarisation or AC impedance technique.

Table 1 — Determination of onset of corrosion at assessment technique

Corrosion risk shall be determined by all obtained information about steel, concrete properties and environments. With no indication of corrosion initiation, the risk of corrosion shall be categorised into several levels with respect to items as seen in Table 2, in which the corrosion risk is categorised into very low, low, medium, high and very high with respect to steel concrete cover and environment. To meet each category all conditions shall be satisfied for steel, concrete cover and environment.

Table 2 — Category for corrosion risk at assessment

As for steel, the conditions shall be measured for half-cell potential, polarisation and galvanic current monitoring.

As for concrete cover, the conditions shall be measured for moisture level in concrete structure, porosity (i.e. pore distribution) and alkalinity of pore solution.

As for exposure environment, the conditions shall be measured for concentration of external chloride ions, concentration of CO₂ in atmosphere and weathering (i.e. humidity).

Depending on the corrosion risk, future repair should be determined. Then, a further assessment should be performed to achieve more information on the detailed status of steel corrosion with budgetary planning on the next stage including expected service life, structural state and impact.

A well-organised repair technique shall be selected, considering technical and economic benefit, given environment, budget and etc.

In selecting repair technique, the corrosion risk and service life shall be re-calculated and determined to compare to concrete structures with no repair; this process shall provide quantitative information on benefit of repair techniques.

Repair of concrete structures subjected to steel corrosion shall be required to maintain their performance requirements, complying with the ISO 16311-3.

As for action of repair, autopsy of the status of concrete structure shall be performed in terms of:

— cause of steel corrosion;

— symptom of steel and concrete cover;

— possible strategies for repair;

— budgetary planning;

— expected residual service life.

Possible strategies for repair should include electrochemical treatment and patching with non-corrosive mortar or concrete depending on cause of steel corrosion, symptoms and budgets.

The entire process of repair of corrosion of steel in concrete structures shall conform with ISO 16311-3 and 16311-4.

Concrete structures which are beyond repair should be considered to demolition.

Prior to repair, strategy planning shall be set in a flow as given in Figure 1.

Electrochemical chloride extraction shall be adopted to chloride-induced corrosion, while realkalisation to carbonation-induced corrosion.

As for general corrosion, electrochemical treatment should be adopted to repair the entire structure. At the severe level of corrosion, the concrete structure shall be subjected to demolition. As for pitting corrosion, electrochemical treatment may be optional, and patching method may be an alternative method for repair.

Selection of repair method shall be considered by other options: symptom of concrete cover and its recovery, residual service life, budget and installation easiness. The importance of consideration parameters should be preliminarily ranked and used to determine the repair method.

Simultaneously, service life extension should be determined. The service life with no repair should be determined and the residual service life should be calculated by specified methodologies considering the circumstance surrounding the concrete structure, then the extended life of concrete structures should be in turn determined.

Figure 1 — Strategy for repair and retrofit of concrete structures under steel corrosion

In selecting a repair technique, technical benefit (i.e. increased service life), economic expense, a given environment and budgetary planning shall be considered. In repair, the execution for the prevention techniques is given 7.3.1 and 7.3.2, while the execution for the restoration techniques in 7.3.3 and 7.3.4.

Prevention techniques mainly consist of external treatments: concrete-surface treatment and electrochemical treatment as given in Table 3. Selection of prevention techniques depends on the economic expense, source of steel corrosion, surrounding circumstances of concrete structures, importance of concrete structures and target service life.

Table 3 — List of prevention techniques

Note Preventive techniques used in design (method) of concrete structure are excluded in this document: chemical inhibitors, replacement of Portland cement, coating of steel etc.

The determination of corrosion risk is dealt with in 6.4.2 and the prevention techniques in 7.2.2

Service life shall be also predicted by values for calculating the governing equation, which shall be selected, depending on cause of corrosion.

As appropriate concrete surface treatment, including surface polymer coating and water-repellent tratment (impregnation) restricts access of corrosive ions and molecules from external environments, imposing no corrosion of steel, no test and assessment shall be required in the list of Table 2 in determining the corrosion risk.

In determining the corrosion risk, methodologies should be specified to calculate the service life of concrete structures with concrete-surface treatment.

Note Concrete-surface treatment is included in prevention technique with no influence on steel and concrete cover. In concrete-surface treatment, no aggressive and corrosive ions and molecules are forced to percolate into concrete.

As given in Figure 2, electrochemical treatment formed with an equated electric circuit depends on target, current density and duration:

— cathodic protection;

— electrochemical chloride extraction;

— realkalisation.

As prevention technique, cathodic protection should be selected in sound concrete structure, while electric circuit should be used for repair after the onset of corrosion with respect to the cause of corrosion.

Figure 2 — Schematic of electrochemical treatment in concrete structures

In determining the corrosion risk, the rate of chloride transport and a pH fall should be determined. Concrete properties under electrochemical treatment should be determined.

Depending on types of electrochemical treatment, the current density, voltage and duration of each treatment shall meet the margin for ranges as given in Table 4.

Table 4 — Limitation for electrochemical treatment in concrete structures

In repair for electrochemical treatment, electrochemical chloride extraction and realkalisation should be temporarily adopted about 4-12 weeks depending on the cause of steel corrosion. In electrochemical chloride extraction, the anodic attachment on concrete surface shall secure the electric conductivity during the treatment. After the completion of the electrochemical chloride extraction, a removal of chloride shall be measured in a bulk or in a profile to the cover concrete.

In realkalisation, the solution in the anode shall exceed the alkalinity of the pore solution, usually accounting for 12.5 in the pH. After the completion of realkalisation, the alkalinity of cover concrete shall be identified by spraying the phenolphthalein solution to the direction of the steel.

The steel corrosion can be more or less recovered by the electrochemical chloride extraction or realkalisation. Thus, further assessment for steel corrosion shall be made, after the completion of the electrochemical treatment, if required.

As for patching with non-corrosive mortar, corroded steel should be repaired by chipping-off of contaminated concrete and spraying inhibitive agent solution to the steel after removing rust. Then, non-corrosive mortar is patched to nullify the risk of steel corrosion. In patching process, the concrete contaminated with corrosive ions or molecules such as chlorides shall be removed and sound concrete or mortar is substituted; repair of steel corrosion shall be separately made such as rust-off and inhibitor impregnation, as given in 7.3.4.

To lower or halt the corrosion process, an inhibitive action shall be accompanied, for example, inhibitor impregnation and pore blocking, irrespective of repair method.

To repair concrete cover, electrochemical treatment can be adopted for pore blocking and crack healing.

To reinstate concrete cover, resin impregnation can be adopted to arrest cracking in the concrete cover.

Patching with non-corrosive mortar should substitute for concrete cover subjected to cracking and spalling-off. In patching process, the concrete contaminated with chloride is removed and concrete or mortar is substituted; no need of any further action to repair of concrete cover.

To repair corroded steel, the repair method can be derermined into cleaning corroded steel, replacing by new steel and adding new steel, depending on the degree of corrosion and condition of concrete structure.

In cleaning corroded embedded steel, a measurement of half-cell potential to mapping should be performed to point out the position of corrosion underneath concrete cover. The contaminated concrete cover shall be chipped off and then corroded part on the steel surface shall be removed or blistered off by sand paper or diamond-grit grinders. Then, chemical inhibitors shall be sprayed on the steel surface, follwed by being patched by non-corrosive mortar. After the completion of the entire process, a monitoring of half-cell potential or other corrosion monitoring shall be performed to secure the risk of ring corrosion, which may take place between patching and non-patching regions.

Once the corrosion is propagated on the entire surface at the high degree, the corroded embedded steel shall be replaced by new steel. After removing the corroded embedded steel by chipping out of cover concrete, the new steel shall be replaced, follwed by being patched by non-corrosive mortar. The size and strength of the new steel shall be determined by the safety and structural capacity of concrete structure.

When the corrosion of steel is severe and thus the structural capacity of the concrete stucture is significantly reduced, new steel should be added. After chipping out of cover concrete, the corroded steel shall be repaired by removing rust on the steel surface and spraying inhibitive agents. Then, a new steel shall be placed, followed by being patched by non-corrosive mortar. To ensure the risk of glvanic corrosion between old steel and new steel, the galvanic current should be monitored during a given duration, if necessary.

Once repair is adopted to concrete structures, the service life shall be determined in terms of the extended service life in specified methodologies to ensure the economic benefit.

As electrochemical treatment is temporarily adopted for several weeks until the sources of corrosive ions, and molecules are removed from the depth of the steel, the service life shall be determined with a given condition.

A modified service life by patching with non-corrosive mortar shall be determined with a given condition.

Details concerning assessment and repair of corroded steel shall be recorded. In assessment and repair, the details of concrete and environment shall be also recorded to verify the cause of steel corrosion, degree of corrosion and the time to corrosion.

When preventive measures or repair methods are adopted, the details on materials, electrochemical values of steel rebar, concrete and environments shall be recorded.

Such records as well as drawings and related documents shall be preserved by the owner for safe-keeping and future references.

1. 
   
   (Assessment technique for steel corrosion)

In assessing the status of steel in concrete structures with respect to corrosion, visual examination, half-cell potential, polarisation technique, AC impedance and galvanic current monitoring are representatively used. Of them, one or more techniques shall be chosen to assess corrosion of steel in concrete structures and information is used to determine a further action on repair.

Visual inspection is often used for initial stage of assessment.

— Half-cell potential measurement provides qualitative information on whether the steel embedment is corroded. Potential mapping should be made to achieve the distribution of the corrosion risk for entire concrete structure with empirically and statistically determined data set. Thus, to confirm the state of steel corrosion, concrete properties and environmental information is accompanied.

— Galvanic current monitoring, as a continual assessment technique, provides qualitative information on whether the steel embedment starts corrosion. At the onset of corrosion, there is a sharp increase in the galvanic current by 2 or 3 orders from the passive state as seen in Figure A.1. The ladder cell system, as being modified by the galvanic current monitoring, is installed in concrete structure to monitor the risk of steel corrosion with time.

— Linear polarisation technique provides quantitative information on the status for steel corrosion. It takes about 0,1-0,5 hours to achieve data for the status of steel corrosion at a single steel. However, it is usually used in laboratory to date. To achieve the corrosion status in in-situ, the guard ring is used to confine the realm of the steel with a given corrosion potential or the Tafel’s extrapolation is used to determine the anodic and cathodic reactivity.

— AC impedance technique provides quantitative information on the steel corrosion. However, it is usually used in laboratory to date. The noise and vibration are minimised, and the measurement area is accurately considered.

Key

G_c galvanic current

p passive

t time

a active

Figure A.1 — Representative description of galvanic current monitoring to detect the onset of corrosion by a sharp increase

Bibliography

[1] ISO 12696:2022, Cathodic protection of steel in concrete

[2] ASTM C 876 Standard test method for corrosion potentials of uncoated reinforcing steel in concrete

[3] ACI 222R Protection of metal in concrete against corrosion

[4] ACI 546R Guide to concrete repair

[5] ACI 562 Code requirements for assessment, repair, and rehabilitation of existing concrete structures and commentary

[6] BS EN 1504, Products and systems for the protection and repair of concrete structures

[7] BS EN 14038‑1, Electrochemical realkalization and chloride extraction treatments for reinforced concrete. Realkalization

[8] BS EN 14038‑2, Electrochemical realkalization and chloride extraction treatments for reinforced concrete. Chloride extraction (Drafting)

[9] BS EN 12696, Cathodic protection of steel in concrete

[10] ACI 345.1R-92, Routine Maintenance of concrete bridge

[11] BS EN 15183, Corrosion protection test

[12] D444 part 3, Corrosion of steel in concrete; protection and remediation

[13] D53 Guide to the maintenance, repair and monitoring of reinforced concrete structures

[14] CSA S448.1-93: Repair of Reinforced concrete in Buildings

[15] Broomfield, J.P., (2003) Corrosion of steel in concrete, J.P. Broomfield, CRC Press