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Location:
Trondheim, Norway
Date:
16 June 2008 - 19 June 2008
Contact:
Harald Justnes
Tel:
Fax:
Email:
Harald.Justnes@sintef.no
Website:
http://www.icaar2008.org
The ICAAR is the most important conference in the world on deleterious alkali-aggregate reactions and related topics from adjacent science disciplines, eg. mineralogy/geochemistry, physics, mechanics, etc. In October 2004, the 12th ICAAR in Beijing was attended by nearly 300 delegates from 25 countries on all continents. The ICAAR dates back to 1973 when the first ICAAR was held in Koge, Denmark, and successive ICAARs have gone to Iceland, UK, USA, South Africa, Canada, Japan, and Australia.
Background of deleterious alkali-aggregate reaction (AAR)
The most wide-spread variety of AAR is ASR (alkali-silica reaction), in which alkalies from the cement paste produce a gel with silica from the aggregate, in a water-saturated environment. Due to its hygroscopic and hydraulic nature, the silica gel attracts water and reacts with it, physically expanding and disintegrating the surrounding concrete, weakening the structure. This reduces the designed service-life, compromises reliability, and increases maintenance. Annually, the global budget for partial rehabilitation or complete replacement of ASR damaged structures amounts to nearly two billion euro.
Deleterious ASR can be identified most conveniently using impregnation-fluorescence petrography on plane and thin sections in an optical microscope. Appraisal of existing structures requires both a detailed characterization of the material as well as a thorough structural assessment. Prevention of future ASR in structures yet to be built is achieved by restricting allowable alkali-concentrations of the binder as well as by adding blast-furnace slag, fly ash, silica fume, or other supplementary cementitious materials, or both. Alternatively, ASR may be prevented by limiting the content of potentially deleterious constituents in the aggregate material.
Despite the enormous research effort spent on ASR over the last three decades, much of the undesired silica dissolution is still not fully understood. Rock types classified as innocuous to ASR in one region may by experience prove violently alkali-reactive somewhere else. However, criteria to distinguish good from bad and ugly are still lacking. In the global ASR-research community, consensus is emerging that knowledge from mineralogy and geochemistry may contribute to finding a solution.
