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Durability testing of alkali-activated materials
Technical Committee 247-DTA
General InformationChair: Prof. John L. PROVIS
Secretary: Dr. Frank WINNEFELD
Activity starting in: 2012
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:
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.
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 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.
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:
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.