OCM : On-site Corrosion Condition Assessment, Monitoring and Prediction

Technical Committee OCM


General Information

Chair: Dr. Carmen ANDRADE
Deputy Chair: Dr. Pedro CASTRO BORGES
Activity starting in: 2022
Cluster C

Subject matter

The subject is related to the prediction of the residual life of existing corroding structures. Reinforcement corrosion is one of the major causes of the deterioration of structural concrete, in spite of which its assessment in real structures still lacks standardized procedures for being currently used. In general samples or cores are taken for assessing whether the structure is or not corroding and with respect to the assessment of the corrosion level, electrical potential or resistivity are the current techniques being the measurement of the corrosion rate much seldom applied. Once these data are obtained, the condition of the structure is described, but in general, without any reference to the future evolution of the phenomenon and neither how to link these data with the structural performance. There are Guidances on how to make the tests but nothing about indications of how many samples are needed, or how to classify the degree of risk or damage, etc. It has not being found a comprehensive approach for the corrosion condition assessment and how to integrate it into the actual trend and need of instrumenting (monitoring) the structures to avoid undesirable accidents. Anticipation of the damage to make preventive maintenance is not enough documented. 

The TC will try as well to fill the gap of the prediction of evolution of the corrosion in each particular environment and the calculation of the remaining life until the ad-hoc structural limit state . This subject is not contained in present Codes and therefore there is a gap which needs prenormative documents which could be used to gain experience with the aim to have rules incorporated into the future structural codes.

Terms of reference

The objective of present TC would be the comprehensive treatment of all information for measuring the onsite  corrosion condition in structural concrete and then, from this information and using existing models, incorporate the diagnosis and prediction of the evolution of damage and of the optimum time for intervention.

 The particular goals are:

  • first, to review and update the previous Rilem Recommendations on electrochemical techniques and on chloride analysis for confirming or not the procedures
  • to add new information or complement it with new on site testing methods
  • to develop a general evaluation procedure for the combined consideration of all the information in order to make a comprehensive diagnostic related to corrosion level and present condition of the structure regarding its service life
  • to integrate the data from monitoring and this general procedure

These goals will be applied to new and existing structures:

  • In the new structures the focus will be to the “preventive maintenance” and strategies of advanced prediction of risks of corrosion to anticipate interventions to avoid accidents or colapses. Models of carbonation and chloride advance, as well as chloride threshold values will be discussed and case studies will help to summarize the general guidance methodology of monitoring, inspections, diagnosis and prediction of the risk of corrosion.
  • In new structures, the Deliverables will take into account that the end-user will be engineers specialized in maintenance and experts in chloride and carbonation modelling. The members will make their best to agree on suggestions of indicators of “limit states”and of “aging factors” which help to take decisions on preventive maintenance.
  • In existing structures however, the end users will be structural engineers and the aim of the TC is to provide the material data they need for structural recalculations to verify the serviceability and ultimate limit states.
  • The main unknown aspects have been identified as related to the evolution of the corrosion of the rebar more than to the evolution of the carbonation or chloride content. All aspects will be treated in combination, but with emphasis in the corrosion evolution in function of the environmental conditions. In the existing structures special attention will be paid to the combination of the mechanical strength with the advance of the aggressive fronts and the craking induced by the rebar corrosion.
  • Methods for updating (Bayesian treatment) the information and predicting the evolution will be applied to particular case studies to propose a methodology for corroding elements.
  • Monitoring through embedded or attached sensors has been considered a crucial needed advance by the members of the TC. Special attention will be paid to collect data, to show case studies and to establish criteria for the interpretation, valid for maintenance as well as for structural recalculation. Recommendation on the data needed of the corrosion sensors will be together with complementary  information in order to give guidance for the correct evaluation. The ambition is not only to give guidance for the diagnostic, but also for the prediction and basis for the possible interventions needed in function of the degree of corrosion registered.
  • Another aspect to be discussed is on the appropriate identification of the environmental aggressivity because it is also a non enough well identified aspect when made in combination with the corrosion risk.In summary, the key words are: corrosion, site inspection, condition assessment, diagnosis, prediction and monitoring.

The work is foreseen for a maximum of 4 years: the optimum would be 3 years plus 1 or 2 for the editorial work . It is not expected the need of any Round Robin test.  The work has a practical relevance as the TC will deal with site methods.

It is, in principle, excluded from the scope the following aspects:

  • To assess structures having embedded epoxy coated rebars
  • The assessment of stress corrosion cracking phenomena in prestressing members

Detailed working programme

With respect to the schedule of meetings and events, the plan is:

  1. In 2022, we will organize a Workshop for sharing the knowledge on the subject and discussing previous case studies of monitoring and site inspections. Proceedings will be published.
    1. Review and update of present Rilem Recommendations (listed below)
    2. The work will be by virtual meetings. The scope will be more focused onDeliverables (Recommendations, papers or Guidance documents) responsibility that will be distributed
  2. In 2023, the work on the Deliverables will continue by virtual meetings
    1. Another Workshop will be organized and other proceedings will be prepared
  3. In 2024, the same pattern of work is foreseen unless otherwise is decided.

Technical environment

There are very few TC’s dealing with site information. It seems Cluster C the most appropriate as the ambition is that the information could serve for the structural recalculation.

There was a previous TC 154-EMC “Electrochemical techniques for measuring metallic corrosion” in Rilem of which the Chairlady was the same that presents this proposal.  They were:

  • Polder, R.; Andrade, C.; Elsener, B.; Vennesland, O.; Gulikers, J.; Weidert, R.; and Raupach, M.; “ Test methods for on site measurement of resistivity of concrete”, RILEM TC 154-EMC: Electrochemical techniques for measuring metallic corrosion”, Materials and Structure, Vol 33 (2000), pp. 603-611.
  • Elsener, C. Andrade, J. Gulikers, R. Polder, M. Raupach.- RILEM TC 154-EMC: Electrochemical techniques for measuring metallic corrosion Half-Cell Potential Measurements – Potential Mapping on Reinforced Concrete Structures -Vol 36 (2003) 461-471.
  • Andrade C, Alonso C, Gulikers J, Polder R, Cigna R, Vennesland Ø, Salta M, Raharinaivo A, Elsener B. (2004). "RILEM TC 154-EMC:Electrochemical Techniques for Measuring Metallic Corrosion. Recommendations Test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method." Materials & Structures 37(273): 623-643.
  • . Vennesland, M. Raupach, C. Andrade- Recommendation of Rilem TC-154-EMC: ‘‘Electrochemical techniques for measuring corrosion in concrete’’—measurements with embedded probes Materials and Structures (2007) 40:745–758

These Recommendations describe the theoretical basis of the electrochemical techniques and  some rules for their application in existing structures with some general consideration of for the correct interpretation of the results.

The proposer was also chairlady of the TC, TC 178- TMC – “Testing and Modelling of Chloride Ingress into Concrete" also related in the modelling part with present proposal. The Recommendations and papers published were:

  • Castellote and C. Andrade.- Analysis of total chloride content..- RILEM Recommendation of TC-178-”Testing and modelling chloride penetration in concrete”.- Materials and Structures.- vol 35 (2002) pp 583-585.
  • Castellote and C. Andrade.- Analysis of water soluble chloride content in concrete.- RILEM Recommendation of TC-178-”Testing and modelling chloride penetration in concrete”.- Materials and Structures.- vol 35 (2002) pp 586-588.
  • Castellote and C. Andrade.- Round-Robin test on chloride analysis in concrete- Part I: Analysis of total chloride content..- RILEM Recommendation of TC-178-”Testing and modelling chloride penetration in concrete”.- Materials and Structures.- vol 34 (2001) pp 532-556.
  • Castellote and C. Andrade.- Round-Robin test on chloride analysis in concrete- Part II: Analysis of water soluble chloride content.- RILEM Recommendation of TC-178-”Testing and modelling chloride penetration in concrete”.- Materials and Structures.- vol 34 (2001) pp 589-598.
  • Castellote and C. Andrade.- Round-Robin test on methods for determining chloride transport in concrete.- RILEM Recommendation of TC-178-”Testing and modeling chloride penetration in concrete”.- Materials and Structures.- vol 39 (2006) pp 995-990.
  • C. Andrade, M. A. Climent, G. de Vera  - Procedure for calculating the chloride diffusion coefficient and surface concentration from a profile having a maximum beyond the concrete surface -  Materials and Structures April (2015) Volume 48, Issue 4, pp 863–869
  • . Vennesland, M. A. Climent, C. Andrade .-Methods for obtaining dust samples by means of grinding concrete in order to determine the chloride concentration profile.- RILEM Recommendation of TC-178-”Testing and modeling chloride penetration in concrete”.- Materials and Structures.- vol 46(2013) pp337–344
  • Climent M.A., de Vera G., Lopez J.F., Garcia C., Andrade C.- Transport of chlorides through non saturated concrete after an initial limited chloride supply. Proceedings of the 2nd International Workshop on testing and Modeling the chloride ingress into concrete, C. Andrade and J. Kropp Editors. RILEM Publications. Cachan, France 2000, 173-187.
  • Andrade, F. Tavares, M. Castellote, , I. Petre-Lazars, M.A. Climent, G. Vera – Comparison of the chloride models: the importance of surface concentration – Proceedings (RILEM Pro 51) of Advances in Concrete through Science and Engineering– September 2006, Quebec City, Canada Editor: J.Marchand, B. Bissonnette, R.Gagné, M.Jolin and F.Paradis RILEM Publications S.A.R.L
  • . Vennesland, M. A. Climent, C. Andrade .-Methods for obtaining dust samples by means of grinding concrete in order to determine the chloride concentration profile.- RILEM Recommendation of TC-178-”Testing and modeling chloride penetration in concrete”.- Materials and Structures.- vol 46(2013) pp337–344

In these Recommendations the chloride analysis and its transport at the of laboratory level and how to make predictions from Fick’s equation was treated,  but there are not information on how to assess a particular structure: how many cores and in which zones and how to treat the information (among others).

Regarding other active TC at present related to this objective, it can be mentioned that:

  • TC RILEM TC 289-DCM-“Long-term durability of structural concretes in marine exposure conditions” which is dealing with the collection of data in old structures, but it is not addressing the methods to obtain the samples.
  • TC ECS : “Assessment of electrochemical methods to study corrosion of steel in concrete” This TC has different objectives as it is focused to the measurement in the laboratory of the different corrosion techniques.

Expected achievements

With respect to the subjects the expected Deliverables, they will be:

  1. On testing methods
    1. Updating of the Rilem Recommendations on:
      1. Corrosion potential
      2. Resistivity
      3. Corrosion rate
      4. Analysis of chloride content on site (there are several and it will be decided whether to maintain them or merge in a single one)
      5. Site measurement of carbonation depth (there is a very old Rilem Recommendation that has to be updated and additionaly the phenolftalein has been classified as dangerous substance and new pH indicators should be recommended)
    2. Sensors: with respect to this Recommendation it is needed a thorough revision and it will be decided whether the existing Recommendation will be splitted in several ones
      1. Description of type of measurements and objective of the data collected. Robustmess of the sensors.
  2. On Procedure methodologies
    1. General framework for the corrosion condition assessment, diagnosis and prediction
      1. This document will take into account the integral evaluation of present condition of the structure: how to combine the information of different tests. Where to test and how many samples. Spatial and in concrete depth variation influence. Representativity.
      2. Application of updating (Bayesian) procedure for the individual phenomena: how to generalize the limited collection of data with previous data Compilation of needed information for recalculation by structural engineers. Application of existing models for prediction of evolution of the damage
      3. Diagnosis, prediction of the time to intervention and possible interventions
  3. Diagnosis and prediction through corrosion and damage monitoring
    1. New and existing structures will have a different treatment
    2. Where and how many sensors to be installed. Intervals of measurements
    3. How to interpret the results reading the condition assessment fo the corrosion risk or the verification of structural limit states.
  1. Case studies on corrosion condition assessment and on monitoring

Group of users

The outcome of this TC will be of interest for practitioners and designers.  It will be as well by academics and those organizations related to standards related to existing structures. However, the most direct end users will be engineers of maintenance, consultants, inspectors and structural engineers.

Specific use of the results

The procedures should be at pre-standard format: standardization bodies, fib for its Model Code, academics, inspectors, laboratories and design engineers.