Distribution and Significance of Alkali-Aggregate Reaction in Southern Norway


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Title: Distribution and Significance of Alkali-Aggregate Reaction in Southern Norway

Author(s): V. Jensen

Publication: Special Publication

Volume: 145


Appears on pages(s): 741-756

Keywords: alkali-aggregate reactions; bridges (structures); cracking (fracturing); crack width and spacing; high-alkali cements; inspection; map cracking; structures; Structural Research

Date: 5/1/1994

In 1989, a field inspection of concrete structures in selected geological areas showed that nearly all known structures with alkali-aggregate reaction (AAR) were situated within or close to areas with known potentially reactive bedrock of metarhyolite, metasandstone, metagreywacke, and phyllite. Such areas may, therefore, be interpreted as areas with a high risk of AAR, when local aggregate deposits and Norwegian high-alkali cements are used. To get an overview of the extent of AAR in the whole of Southern Norway, a survey inspection of randomly distributed road bridges and dams older than 10 years was carried out during the summer of 1990. The decision was made to use map cracking as an indicator for AAR and to measure maximum crack width and estimate area percent of map cracking. The data from the inspections of 468 structures have been put into a database (as well as other available information, e.g., laboratory analyses results). A distribution map plot of inspected structures has been constructed and used to locate structures into two types of geological areas, namely, structures located in potentially reactive bedrock areas, and structures located in supposed innocuous bedrock areas. Data processing shows that map cracking is common in structures in Southern Norway and is more frequent in potentially reactive bedrock areas. In potentially reactive bedrock areas, average maximum crack widths and area percent of map cracking is larger than in supposed innocuous bedrock areas. A surprising peak height of increased maximum crack width has been revealed to occur in structural elements built around 1950 to 1960. This peak height is most significant in structures situated in supposed innocuous bedrock areas. The cause of this increased cracking in structures built around the 1960s is unknown but could be caused by a very high alkali content in Norwegian cement at that time.