Subject matter

This RILEM TC is proposed under the suggestion of the CEN TC 51(CEN TC 104)/JWG12/TG1 "Sulfate resistance testing".The primary aim of this TC will be to provide recommendations regarding appropriate test methodologies and protocols for theanalysis of sulfate resistance, in relation with the CEN TC 51(CEN TC 104)/JWG12/TG1.

External sulfate attack is one type of degradations, which can be observed on structures. In most of cases, it can be rather well managed by using the appropriate cement & mix-design. But in the case of new mixtures (in particular with incorporation of high volumes of supplementary cementitious materials), we do not have much experience. In addition, the appropriate tools for prediction are not yet available (models, relevant parameters, etc.). Resistance to such an attack is therefore a key challenge for structural durability. Sulfate-related phenomena are complex (they couple physics, chemistry and mechanics) and existing testing procedures related to external sulfate attack are not appropriate (poor ability to discriminate cements, insufficient accuracy, etc.). More research is needed on this topic to better understand and capture the degradation, which could occur in the field. It is also needed to develop an other approach (focus on other aspects than expansion). A more inclusive assessment of surface damage, including both expansive (scaling) and softening or disintegration types of destruction, is required (as suggested by the outcomes of the NanoCem European Consortium convened by K. Scrivener).

Different tests will be selected, depending on the purpose:

- tests for qualification of cements:

_ reliable, rapid, with appropriate robustness and precision (better reproducibility and which yields improved discrimination compared to the existing procedures)

_ only chemistry needs to be considered

_ not restricted to CEM I (rather focused on blended cements)

- tests applicable to concrete mixtures within a performance-based framework, in order to assess (or compare) the resistance of the mixture with regard to external sulfate attack:

_ simple but relevant

_ a set of tests, instead of a single test based on expansion measurement (including e.g. visual degradation scheme, mechanical strength, assessment of physical properties such as porosity and transport properties, NDT, …). With regard to the expansion measurement, the selection of the test conditions (storage conditions, concentration and volume of the contact solution, sample configuration, pre-curing, …) will be based on the conclusions of the NanoCem European Consortium and of the previous TG1.

The TC work should include the following topics:

- understanding of degradation mechanisms not only involved in lab tests but also which occur in real conditions (e.g. mechanical effects will strongly depend on the size/type of test specimen)

- possible combination with other sources of degradation (cases of seawater (including e.g. competition between chlorides and sulfates in the binding process with the cement matrix), dry climates, …)

- gather field results and/or trials in field conditions on exposure sites

- specific aspect of thaumasite (e.g. temperature aspect), keeping in mind that thaumasite formation is a "second event" of classical external sulfate attack, according to the NanoCem results.

- critical analysis and recommendations on test procedures

The proposed methodology should be applicable to mixtures, which incorporate high volumes of SCM (with Portland clinker).

Terms of reference

The TC activities will run over a five-year period. The intended period of work ranges from 2013 to 2018. Regular meetings are planned (2 per year), as well as additional opportunities to exchange knowledge (e.g. workshops), possibly in conjunction with RILEM weeks.

The committee will start with a relatively small group of international experts working on the subject. Some of them will be members of the CEN TC 51(CEN TC 104)/JWG12/TG1 "Sulfate resistance testing". Members will be recruited from academic and research institutes, as well as from the industry.

Round Robin Tests will be undertaken, in order to investigate the role of some parameters, as well as to assess repeatability/reproducibility of the proposed test methods. The recommendations for the various tests methods, in agreement with the mentioned purposes, will be based in particular on the results of these RRTs.

Detailed working programme

The kick-off meeting of the TC will address the following items: introduction of members, suggestion of new members, plan of activities, list of contents for the STAR, preparation of an initial workshop, and selection of Work Packages if required.

A workshop will be held after the kick-off meeting of the TC, well focused on the TC's topics, in particular in order to get an overview of experience and difficulties related to the methods used by the TC members and in order to better orientate the TC further work.

Different Work Packages can be considered:

- Review on degradation mechanisms

- field aspects (location, environment, consequences, mechanical load, etc.)

- State-of-the-art on methods

- Experimental work

- Drafting of recommendations

A final international conference or workshop will be held.