Norwegian Concrete Assosiation Publication no. 21 “Durable concrete with alkali reactive aggregates” & Norwegian Concrete Assosiation Publication no. 32 “Alkali aggregate reactions in concrete – Test methods and laboratory requirements” Amendment valid from April 15th 2008, revised April 12th 2012. BACKGROUND, PROCEDURE AND PUBLISHING Following four years of experience with the application of NB 21 & 32, the Norwegian Concrete Association in 2008 decided to emphasise certain issues in order to clarify and facilitate the application of the guidelines. One topic only of the guidelines is subject to additional limitation, and it was decided to issue the additional parts as an amendment to the existing document, to be enclosed to the latter for future purchase of the document. In 2012, the experience with extensive testing of fly ash cement was reviewed and the acceptance procedure and criteria adjusted. This enables preliminary approval based on test results after six months of testing.