- Project plans
- Project activities
- Legislation and standards
- Industry context
- Specialist wikis
Last edited 08 Dec 2020
Alkali-aggregate reaction (AAR)
However, the material had a 'guilty secret' that was only revealed by research in the USA during the 1930s. In some circumstances, an expansive reaction can gradually occur between aggregate constituents and alkaline hydroxides from the cement, causing damage to the hardened concrete within structures.
This has become known as 'alkali-aggregate reaction' (AAR), or most commonly and more specifically, 'alkali-silica reaction' (ASR). This AAR family of mechanisms is by no means the most frequently encountered threat to concrete durability or the serviceability of structures, but it can be a serious issue when it occurs.
 Getting to grips with AAR
Over more than 40 years, I have been privileged to witness practising engineers and applied scientists getting to grips with AAR worldwide. I believe we now understand the several reactions, including how to recognise them in existing structures and manage the situation, but crucially also including how to determine any possible AAR potential in new works and take effective precautionary measures.
However, challenges remain, especially as appreciation of the potential threat from AAR is not universally or equally appreciated everywhere in the world, and we are still finding types of structure that behave exceptionally. Overall, the prospects are encouraging for both a declining incidence of AAR damage and successful approaches to management and/or repair of affected cases.
 Related articles on Designing Buildings Wiki
Featured articles and news
Shedding some light on the new Building Regulations.
Interview with historic built environment surveyor.
Upgraded membership category now requires assessment.
Temperature in buildings, explained on DB
Main barrier to entering the profession, new study reveals.
On Levelling-Up and Regeneration Bill.
Over 70 managers and organisations shortlisted for the 14 awards.
From biometric to electrical current, chemical and more.
Changes are due to come into force on 1st October 2022.
Heed advice and insight of this report IPA tells the government.
From the Commonwealth Association of Architects.