1. Scope This Guide has been written by Canadian experts on the diagnosis and treatment of concrete structures affected by alkali- aggregate reaction (AAR). The purpose of the Guide is to provide information on the signs and symptoms of concrete affected by AAR, how to identify AAR and distinguish it from other mechanisms of concrete deterioration, and how to assess the extent and severity of AAR in concrete. It also provides advice on the best ways of evaluating, maintaining, and treating structures affected by AAR. This Guide will be of use to people involved in such work and to the owners of structures affected by AAR.