178-TMC : Testing and modelling chloride penetration in concrete

Technical Committee 178-TMC

General Information

Chair: Dr. Carmen ANDRADE
Deputy Chair: Prof. Dr.-Ing. Jörg KROPP
Activity starting in: 1997
Cluster C

Subject matter

- The mechanism of chloride ingress into concrete shall be studied in its different aspects : penetration by absorption, diffusion and migration should be well differentiated. Definitions and differentiation have to be addressed. The influence of several parameters such as external concentration or binding capacity shall be explained. The meaning of the different Diffusion Coefficients shall be also addressed. - This background will serve for the purpose of: - analyzing the different testing methods more currently used in the different countries. - summarizing the different models deve-loped to appraise the penetration mecha-nisms : absorption, diffusion and migration. - Concerning the test types, consensus will be tried on those more adequate to be used in a design phase. Test procedures for existing structures shall be agreed as well. Distinction between both steady-state (diffusion cell) or non-steady-state (ponding) shall be provided. - In the modelling, different levels of sophisti-cation shall be taken into account. From simplified methodologies to finite element methods shall be reviewed in order to improve the understanding of the models and to limit their ability to be used for predictive purposes.

Terms of reference

- Chloride penetration into concrete is one of the most relevant matters related to structural durability. RILEM has the largest number of specialists to undertake comprehensive work in this subject. - The international approach is needed for the following reasons: * There is no internationally agreed test for testing chloride penetration into concrete and the existing ones lack the ability to be used for long-term prediction. * The modelling to enable such prediction still also lacks international consensus. * Round robin tests are needed in order to clarify the sensitive aspects of the testing methodologies. - The time necessary to carry out the work is estimated at 4 or 5 years. - The work shall be performed by means of meetings. The members shall make bibliographic surveys, experimental (round robin) tests and computer (modelling) work.

Detailed working programme

The first step shall be the discussion of the fundamentals in order to standardise the background of the members. A state-of-the-art report shall be the result of this phase. Afterwards, the work will be divided into two aspects: 1. Tests. The steps foreseen are : 1.1. Collection and comparison of existing methods and testing variables, on : - Diffusion cells (steady state) - Ponding methods (natural and accelerated) - Migration tests (steady and non-steady conditions) - Resistivity measurements 1.2. Round robin tests on the selected methods 1.3. If needed, production of RILEM Recommendations. 2. Models 2.1. Analysis of the background of the different models, and on the initial and boundary condi-tions of the different solutions of Fick's law. 2.2. Discussion on the limits of application of these models for predictive purposes. Round robin test for comparative predictions. 2.3. Optimum framework of a model. 2.4. Simplified models for design purposes. 2.5. A state-of-the-art report and, if possible, a RILEM Recommendation on the use of the models, will be the final result.

Technical environment

RILEM has previously paid attention to this subject by recently organizing a workshop (Paris-1995) through TC-116. It has been precisely within this TC where the need for more extense work has been identified. In North America, ASTM and AASHTO have standarized methods. As well, SHRP has produced reports on this subject. - In Europe, several standards in preparation contain the need of developing test methods for chloride penetration. - The work of the proposed TC shall be to provide guidance for interpretation of the existing tests in order to facilitate their use and define their limits for predictive purposes. Only if the existing methods are considered insufficiently reliable will the TC address the proposal of other methods. - Regarding the modelling, there are also existing initiatives (SHRP, HETEK) ; however a comparative analysis is needed in order to limit their reliability and clarify the possibilities of the different models. - The subject of chloride penetration is considered to fit into present RILEM work on two levels : * The microstructural level by trying to summarize the material science background. * The relation to service life prediction.

Expected achievements

- An international approach to the subject is needed in order to take into account all climates and environmental conditions. - The TC is expected to produce : * A state-of-the art report on chloride penetration mechanisms. This state-of-the-art should contain definitions. * A state-of-the art report on testing methodologies. Identification of the sensitive variables. * A state-of-the art report on chloride penetration modelling. - Finally, depending on the work, RILEM Recommendations could be prepared on : * Test methods * Use of models for prediction of service life * Simplified methodology of durability design (chloride attack). - The users will be mainly academics and researchers, although the simplified methodology will be addressed to practitioners and engineers.

Group of users

The state of the art will be of interest mainly for academics and testing laboratories. The recommendations will be of interest for testing laboratories, practical engineers and standarization bodies.

Specific use of the results

The evaluation of the durability of concrete is becoming a greater demand. However, there are no test methods (performance tests) whose results could be used to predict the long term behaviour of concrete in chloride containing atmospheres. One of the reasons for this lack of suitable methods is that many aspects of chloride penetration remain unknown. The results will try to clarify the mechanisms governing the chloride ingress into concrete and the recommendations will be used for predicting service life and assessing the concrete quality with regard to durability.