Alkali Silica Reaction







Preface

New Zealand has been fortunate that despite the use of reactive aggregates in concrete, there have been few cases where damage due to alkali aggregate reaction (AAR) has necessitated extensive remedial repairs. This has largely been due to the early recognition of the potential for reaction and careful use of low alkali cements in areas where there was the greatest risk

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The first edition of this publication drew on findings of extensive studies by DSIR Chemistry Division and the Ministry of Works and Development during the 1950’s and 1960’s. These were reviewed by a working party, chaired by David Barnard of CCANZ, to prepare guidelines that could be used to minimise the damage caused by AAR in future construction. While all members of the Working Party contributed to information gathering and decisions required to produce this document, D.A. St John, DSIR Chemistry Division, undertook the principal editing and writing role. This reflected his considerable experience of New Zealand alkali aggregate reactions and knowledge of international research.



Since then, ongoing work by D.A. St John and R.L. Goguel of Industrial Research Limited (formerly DSIR Chemistry Division) and S.A. Freitag of Opus International Consultants Limited (formerly Works Consultancy) has clarified the extent and severity of the reaction in New Zealand, and explained some unusual cases of AAR observed in concrete structures. Information gained from these studies includes the contribution of alkalis from aggregates (often in amounts outweighing the contribution from other sources), the applicability of tests for assessing aggregate reactivity, greater understanding about the behaviour of greywacke aggregates, and the fact that many precautions only alleviate the reaction, rather than prevent it. There have also been significant developments in the management of AAR internationally since the 1991 edition was published.



There still remain unanswered questions, but it is believed that this edition will provide sufficient information for users and manufacturers of concrete to use materials available in New Zealand with minimal risk to damage from AAR. It is hoped that the electronic format will permit appropriate revisions to be made with minimal effort in future to accommodate local and international developments.





S.A. Freitag R. Goguel



N.B. Milestone





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