Subject matter

The purpose of this proposed Technical Committee (TC) is to develop and promote a performance based testing concept for the prevention of deleterious Alkali Aggregate Reactions (AAR) in concrete. Strong emphasis will be put on the implementation of the RILEM methods and recommendations as national- and international standards.

Avoidance of AAR in future structures is of great importance, and the ways to achieve this will be covered by the work programme proposed by this TC. Development of performance test methods to examine the potential alkali reactivity of particular concrete mixes to be used in a project has already been focused on in the work programme of a previous TC, i.e. TC219-ACS. In the work programme of TC 219-ACS, it was taken into account the mitigating effect of supplementary materials such as fly ash or slag etc., or the specification of low alkali levels in the mix. By using such mitigation measures, a much wider selection of aggregates can be used safely while increasing the sustainability of the concrete and aggregate industry. Although such draft performance tests have been under preparation, there is still a necessity to finalize and validate these test methods by international inter-laboratory trials and correlate the performance test results with field exposure sites. Performance testing of special types of concrete (e.g. containing lightweight or recycled aggregates, fibres etc) also needs to be studied further. As soon as the necessary validation is finished, it is the intention to publish these methods as RILEM Recommendations.

An important additional tool in validation of the performance testing concept is to make an assessment of the link between the accelerated results from the laboratory and behaviour of these concrete mixtures in real field structures. Tins will be carried out by compiling the main findings from exposure sites worldwide, preparing an overview of "lab-field correlation" from exposure sites and real concrete structures in services. The objective is to establish a link between outdoor exposure sites dedicated to AAR investigations and located in different parts of the world, in order to generate an international database on the effect of environmental conditions on the kinetics of AAR. Ultimately, this will allow the development of new specifications for reducing the risk of deleterious expansion and cracking development in concrete structures due to ASR in different environments.

One of the important "missing links" in the international AAR research is how to measure the amount of potential alkalis to be released from various types of aggregates in the laboratory, under accelerated conditions. It is also of important to evaluate the potential alkali recycling which in some instances have been reported. This is of particular importance for massive structures having long-service life, e.g. dams, where the contribution of alkalis from aggregates is believed to produce damaging AAR despite the fact that the concrete has been designed to meet current specifications for avoidance of AAR. Various test methods have already been proposed, and it is the intention in this proposed TC to finalise and validate a test method for alkalis released by aggregates, while compiling results from exposure sites and concrete structures worldwide in order to assess the "true" levelof alkali released from various aggregates. As soon as the necessary validation is finished, it is the intention to publish this method as a RILEM Recommendation.

It is well known that synergistic reactions such as freezing and thawing and delayed ettringite formation (DEF) can exacerbate the effects of AAR and can complicate its diagnosis and management. It is however not the intention in this proposed TC to include these issues.

Terms of reference

The proposed TC will work for the full 5 years of its allowed life, based upon the nature of the performance tests. Much of th eground work for these performance tests has been carried out by the previous TC 219-ACS, in the form of draft test methods and State-of-the-Art Reports. However, due to the nature of AAR, being a slow reaction, it is necessary to validate these performance test results with exposure site measurements which necessitate the full 5 year term to reach reliable correlations.

The objective of finalizing and validating the performance testing concepts to avoid AAR in future structures will be achieved by organised international inter-laboratory trials and round-robin testing. This will make use of the wide body of expertiseavailable through the participating members and their entities. 

The main objective of estimating the alkali release from aggregates is to achieve an assessment of the total (reactive) alkali content in concrete. A proposed RILEM AAR-8 test method is considering different test parameters of measurement. It is necessary to investigate and obtain more experience with a common method that takes into account different parameters like, different temperatures, size of aggregate particles, extraction solution, etc. The analysis of different aggregates could give information about the more realistic test method to estimate the potential contribution of alkalis in the field concrete. It is necessary to carry out a round robin test to analysis the possible dispersion of the method and the accuracy of the results. For the round robin test it is necessary about two years for selection of different types of aggregate, test them and analyses the results to extract conclusions. Finally, the validated test methods that reliably estimate the total alkali content of concrete will be published as a RILEM recommendation.

Main of the members will be invited from TC 219-ACS on AAR, though new members are encouraged and will be welcome.The TC is aiming to have a wide international membership which helps to promote the eventual international use of RILEM methods and recommendations. Thus, much communication will be by e-mail and making use of web-site solutions. However, physical meetings will still be the centre of its activities and wherever possible these will be co-ordinated with major relevant international conferences to facilitate attendance. Meetings will also be arranged in locations where laboratories are carrying out performance testing and/or have established outdoor exposure sites. The TC will also apply new ways of electronic communication during the meetings, enabling participation of members without physically being at the venue of the meeting.

Detailed working programme

WP1: Performance testing; Accelerated testing in laboratory.

Proposed task group leader; Dr. Terje F. Rønning, Heidelberg Cement Northern Europe, Oslo, Norway.

WP2: Performance testing; Laboratory vs. field; Exposure site.

Proposed task group leader; Professor Benoît Fournier, Geology and geological engineering Department, University Laval Quebec. Canada.

WP3: Performance testing; Assessment of detailed alkali household in concrete, including internal aggregate release,recycling and external supply.

Task group leader; Dr. Esperanza Menéndez Méndez, Institute of Construction Science, "Eduardo Torroja" (CSIC), Madrid,Spain.