247-DTA : Durability testing of alkali-activated materials
Technical Committee 247-DTA
Deputy Chair: Dr. Frank WINNEFELD
Activity ending in: 2019
The primary aim of this TC will be to provide recommendations regarding appropriate test methodologies and protocols for the analysis of the durability of alkali-activated binders, mortars and concretes (hereafter “alkali-activated materials”, AAMs). This has been identified through the work of TC 224-AAM as being a key issue facing the development of AAM systems for large-scale deployment as a potentially environmentally beneficial construction material. The majority of existing durability testing methods which are standardised worldwide, and widely applied in the testing of construction materials, have been developed specifically (either explicitly or implicitly) for application to the chemistry of Portland cement binder systems. This means that the test protocols have in some cases been identified as being either sub-optimal or entirely unsuitable for application to the analysis of AAM durability. This TC will address the key scientific questions surrounding the application of standard test methods to AAMs, with particular reference to the following areas:
- Chloride penetration
- Sulfate attack
- Freeze-thaw and frost-salt processes
- Alkali-aggregate reactions
Terms of reference
This TC will encompass the specific fields of alkali-activated slags and ashes, geopolymers, blended cements, and other emerging technologies, and will bring together leading practitioners from academia, government laboratories and industry in an international forum. We will use as a starting point the recommendations provided by TC 224-AAM regarding the applicability of various testing protocols in the analysis of the selected aspects of AAM durability, and will use this background to develop and carry out a round-robin testing program utilising standardised alkali-activated paste, mortar and concrete formulations.
The membership will be carefully selected to ensure that the TC participants are able to contribute in a meaningful and important way to the work of the TC, including committing time and resources to the test program. A TC membership of around 20-25 members will be sought. The number of corresponding-only members from research institutes will be restricted, as the focus of the TC will be on achieving outcomes and generating new information. Participation from industrial colleagues will certainly be encouraged, both as direct contributors to the test program where possible (through provision of materials, input into mix design and curing condition selection, and/or directly conducting testwork), and also by providing feedback and insight regarding the progress and focus of the testing program.
Working groups will be established within the TC structure to focus on each of the areas of durability testing listed above. The selection of five durability focus areas within a TC of 20-25 members will necessitate the involvement of the majority of TC members in multiple working groups to enable successful round-robin programs to be conducted in each area.
Detailed working programme
We plan that the work of the TC will be completed in a 5-year period. The TC will aim to meet in full at least once every year to provide for a full discussion of outcomes and objectives, with the possibility of additional working group meetings (either in person or via teleconferencing) more regularly than this.
The activities of the TC will be scheduled as follows:
Year 1 – Initiate collaborative networks, select and source materials and mix designs to be used as the basis for testing, commence preliminary analysis of raw materials and sample formulations, commence selection of test procedures to be utilised
in round-robin tests. Commence „natural exposure‟ test programs (atmospheric carbonation, outdoor freeze/thaw) for parameters where laboratory tests are simulating such in-service conditions.
Year 2 – Initiate round-robin durability testing program: exposing samples of selected mix designs to the selected accelerated testing regimes and compare results. Samples will be exchanged and tested at regular intervals for the remainder of the project lifespan. Commence testing of different raw material streams with comparable mix designs under corresponding test conditions, with a particular view towards determining the robustness of the accelerated test outcomes with respect to mix design and raw materials selection.
Year 3 – Continue analysis of the robustness and applicability of test methods; begin to discard methods which are seen to be unreliable in the early years of work, and focus on preferred methods. Symposium to be held either in Year 3 or early in Year 4, for participants to share and discuss preliminary results and to select targets for the remainder of the project. Prepare and release document(s) outlining initial recommendations based on work in Years 1-3, for publication in Materials & Structures if appropriate.
Year 4 – Finalise round-robin testing program and validate recommended testing methods in each area by comparison with long-term exposure data as these become available (samples which commenced exposure in year 1). Symposium to be held either in Year 3 or early in Year 4, for participants to share and discuss results and to select targets for the remainder of the project. Discussions will also be held with regard to planning for the establishment of a future TC to build from the work of the current TC if appropriate.
Year 5 – Finalise results of all testing, compile all data, complete analysis and prepare final project reports. Develop and release final recommendations document, specifying performance-based testing protocols suitable for the analysis of the durability of a wide range of alkali activated material formulations.
It is expected that the TC will involve participants from Australasia, Asia, Eastern and Western Europe, and North and South America. Researchers with expertise in standards development for Portland-based cement systems (not specifically from a background in alkali-activation) will be invited to participate, so the TC will be able to utilise their skills and understanding in application to this newer class of materials. Research in the area of alkali-activated materials is active in academia, government laboratories and commercial environments worldwide, and it is expected that the TC will draw its membership from across this range of backgrounds.
The concept for the formation of this TC has resulted from the work program and outcomes of TC 224-AAM (chair J.S.J. van Deventer, secretary J.L. Provis), which is due to be concluded in 2012. Several of the members of that TC have expressed a strong interest in participation in the proposed TC. However, the membership of the new TC will be significantly different from the membership of TC 224-AAM, given the specific focus of the proposed TC on issues of alkali-activated concrete durability, compared to the broader interest of TC 224-AAM in issues of binder chemistry in general. The recommendation for the formation of this proposed TC, specifically focused on durability testing methods, is one of the key outcomes of the work program of TC 224-AAM. A key point of reference will be the connection between binder degradation (as is usually measured in accelerated durability tests), and the loss of alkalinity and consequent corrosion of embedded steel in alkali-activated binders. Steel corrosion is usually the key mechanism of degradation of reinforced concretes, meaning that this is the most important performance parameter which needs to be understood, and we will aim to connect the testing methodologies to the likely effects observed in terms of steel corrosion in service.
We propose that this TC be placed in Cluster D (“Durability and Deterioration Mechanisms”), and the work of previous and current TCs in that cluster. There are existing or previous TCs who have worked in each of the areas highlighted in the scope of the proposed TC, where those TCs have worked with specific reference to the analysis of Portland cement-based materials, and we will make full use of the outcomes of their work to guide and motivate the test programs of the proposed TC. Specific TCs which have produced or which are producing important outcomes for the proposed TC include: TC 117-FDC, TC 176-IDC, TC 178-TMC, TC 211-PAE, TC 219-ACS, TC 235-CTC, TC MCT, and TC TDC.
The work of the proposed TC will also align to some extent with the work of TC 238-SCM (in Cluster B), with some overlap in membership between the two TCs, considering the shared interests in the chemistry of SCMs, either combined with Portland cements or in non-Portland based binders.
It is anticipated that each of the five working groups will deliver a set of recommendations based on round-robin tests of standardised alkali-activated material mix designs according to specific durability testing protocols in their respective areas of interest. The recommendations will be focused on answering the questions:
-What is the best method for testing, in a laboratory environment, the likely durability of an alkali-activated binder or concrete according to specific modes of degradation?
- Which parameters of mix design and/or sample conditioning show the greatest impact on the test outcomes, and how do these correspond to likely in-service performance?
- How can it be recommended to formulate an alkali-activated material which is as highly resistant as possible to each form of aggressive exposure conditions?
These recommendations will be prepared in a format suitable for publication in Materials and Structures.
We will also host a public symposium/workshop in Years 3/4 of the TC work program, which will invite participation from across the research community and provide opportunities for the wider dissemination of the outcomes of the test program. It is intended that this will be attached to a major international conference, to maximise the international participation in a way which is not possible for a stand-alone event.
Group of users
Academics, testing laboratories, regulators, industrialists, and practitioners will all be able to make use of the recommendations provided by the TC.
Specific use of the results
The results will be used directly by regulators and practitioners, as the availability of validated testing protocols for the assessment of the performance and durability of AAM binders and concrete is essential in the widespread acceptance of these materials. The potential reductions in CO2 emissions which may be achieved through the use of alkali-activated binders are both economically and environmentally significant – and while the precise life-cycle based quantification of the achievable emissions savings remains the subject of ongoing work, developments in the understanding of durability, and thus service life, are essential in this area. The performance of these materials in scenarios requiring resistance to aggressive exposure conditions must be validated prior to use in „responsible‟ applications in infrastructure elements, and the work of the proposed TC is essential to this. The commercial uptake of alkali activation technology in the developed world has been greatly hindered by the absence of this information in a readily accessible format to date, and the outcomes and Recommendations which will result from the round-robin testing program will provide an accurate and concise overview of the expected performance of a well-designed alkali-activated binder or concrete, highlighting both advantages and limitations when compared with other technologies available in the market.