EBD : Test methods to evaluate durability of blended cement pastes against deleterious ions
Deputy Chair: Dr. Prannoy SURANENI
In the context of climate change, the use of supplementary cementitious materials (SCMs) opens new possibilities in terms of reducing the embodied carbon of concrete and extending the service life of reinforced concrete. However, the rapid emergence of new SCMs triggers the need for efficient and reliable test methods, not only for reactivity but also to establish the effect of these SCMs on long-term concrete durability. After the success of the TC-267-TRM on testing SCM reactivity, this committee aims to establish testing methods to investigate the effect of SCMs on transport-related durability properties. Although durability includes several degradation mechanisms, the primary focus of the proposed TC is on understanding and assessing transport properties in cementitious systems with SCMs. Transport has a strong impact on many degradation mechanisms, including chloride ingress and sulfate attack, which will be the two mechanisms in the scope of the TC.
For the case of chlorides, at the concrete scale, several methods have been developed either to mimic field conditions (e.g., the bulk diffusion test), to obtain diffusion coefficients rapidly with electrical acceleration (e.g., non-steady-state and steadystate migration tests), or to provide indicators of durability (e.g., rapid chloride penetration test, bulk resistivity, and formation factor measurements). It should be noted that the interpretation of such tests might be complex – they provide a single value which is in reality controlled by several different mechanisms (e.g., pore structure, pore solution composition, chloride binding, and/or macro-scale effects). The situation is similar for sulfate attack, with several types of tests existing on mortars and concrete to test chemical attack (e.g., full-immersion) and physical attack (e.g., semi-immersion), but significant debate remains with respect to such tests (e.g., size effects for a layered degradation process) and the representativeness of field conditions.
Recent work has shown the potential of scaling down testing to the scale of cement pastes some well-known techniques (e.g., migration, bulk diffusion, bulk resistivity, formation factor, unidirectional sulfate penetration, etc.). Doing so has the advantage of significantly reducing the number of variables involved in the testing, potentially accelerating testing, and reducing the labor associated with the testing. The primary aim of the TC will be to evaluate cement paste test methods to evaluate the effects of SCMs in modifying the resistance of cement pastes to the damage that is caused by the ingress of deleterious ions, i.e., chlorides and sulfates. Appropriate testing on cement mortar or concrete will be performed to assess the representativeness of paste results.
Terms of reference
The global aim of the committee is to evaluate test methods at the scale of the cement paste to quantify the effects of new SCMs on transport-related durability (chloride ingress and sulfate attack). The committee is expected to run for 5 years with members recruited mainly from academia and engineering practice. Considering the recent discussion at RILEM regarding PhD student involvement, we will favour the involvement of PhD students in the TC.
The work will include: literature review to obtain consensus on existing approaches, terms and directions for further investigation; round-robin testing of promising experimental methods for chloride ingress in cement pastes; comparison of test results with cement mortar/concrete test results; and recommendations for the most promising test method and educational material to foster its use.
As the industry is embracing new SCMs, a consensus on optimal methods for testing durability of those binders has a direct relevance, not only for evaluating of new SCMs, but also to compare systems investigated in different laboratories.
Detailed working programme
- Initial state-of-the-art and planning of testing phases [Year 1]
Ø Introductory on-line meeting (online, tentatively planned for January 2021)
Ø First in-person meeting (tentatively planned during RILEM Spring Convention in April 2021 in Paris)
Ø State-of-the-art workshop (in-person, tentatively planned for RILEM Week in August 2021 in Mexico)
§ State-of-the-art experimental approaches to test chloride ingress & sulfate attack at different scales (TC members have the opportunity to present the new approaches they developed)
§ Discussion on fundamentals, important parameters, and underlying mechanisms
§ Discussion of the roles of pore structure, pore solution composition, chemical binding, etc. on test results
§ Definition of common language (e.g., binders)
Ø Follow-up work
§ Drafting a white paper summarizing state-of-the-art methods presented at the workshop
§ Exploration of applicability of current experimental/modelling approaches for pastes
§ Selection of 2-3 test methods for phase 1
- Phase 1 – Testing of a limited range of binders with different methods (e.g., fly-ash, slag, calcined clays) [Years 2-3]
Ø Evaluate the most promising approaches
Ø Include “conventional” mortar or concrete testing for comparison (for acceptability by the concrete community)
- Phase 2 – Round-robin testing of the most promising method [Years 3-4]
Ø Wider range of SCMs to ensure global applicability
Ø Estimating of repeatability and accuracy
- Summarizing and dissemination of results [Year 5]
Ø Recommendations for adoption of test methods for binder durability (and proposal of a pre-standard)
Ø Final report and online tutorial/training/course for the further dissemination and adoption of test method
Ø Workshop/symposium involving standardization groups (e.g., ASTM, ACI, CEN)
This TC will be part of cluster B on transport and deterioration mechanisms. This TC follows the series of TCs investigating supplementary cementitious materials: from 067-FAB (use of fly-ash in building), to 238-SCM (hydration and microstructure of concrete with supplementary cementitious materials), followed by 267-TRM (tests for reactivity of supplementary cementitious materials). The logical next step is developing a harmonized durability testing approach to measure the effects of SCMs at the binder scale. Such work pursued by a collaboration of leaders of the fields could lead to development of standardized test methods (e.g., Eurocode, CEN/TC51, ASTM, Nordtest…).
This TC would also be complementary to the ongoing work by 262-SCI (characteristics of the steel/concrete interface and their effect on initiation of chloride-induced reinforcement corrosion), 283-CAM (chloride transport in alkali-activated materials), FTC (durability and Service Life of Concrete under the Influence of Freeze-Thaw Cycles combined with Chloride Penetration, TMS (test method for concrete durability under combined role of sulphate and chloride ions) as well as the past TC 178-TMC (testing and modelling chloride penetration in concrete).
- State-of-the-art/white paper(s) on chloride penetration / sulfate attack testing approaches
- Pre-standard methods for testing the effect of binder on the durability against deleterious ions (chloride penetration and sulfate attack tests focusing at cement paste scale)
- Reports of phase 1 and 2 testing phases, in the form of journal papers
- Recommendations for evaluating new binding materials in terms of durability
- Final workshop/symposium (possibly as a joint RILEM/ASTM event)
- Online tutorials/training/course for dissemination of the method
Group of users
Academics, practitioners, industrial scientists and standardization committees.
Specific use of the results
A harmonized test method to simply characterize new SCMs with respect to transport-related durability will greatly facilitate the development and adoption of new cementitious materials.