Guidance on Reinforced Autoclaved Aerated Concrete (RAAC) has been published by several organisations in the last month. The most relevant to Industrial Heritage Network members at the moment is that provided by the 20th Century Society.
AAC is the acronym for “autoclave aerated concrete”, first developed in the 1920s, RAAC, is AAC with added steel reinforcement-hence the “R” at the front. AAC is a special form of pre-cast concrete, that is concrete made in a factory, rather than cast on site. By aerating the mix to provide a bubbly structure, which has been accurately compared to an Aero chocolate bar, the overall weight of the concrete is hugely reduced. The aeration is caused by a chemical reaction initiated when water is added to the mix. Poor initial construction and a lack of maintenance appear to be the main problems, at the moment, leading to the potential collapse of structures using such concrete.
Since most Industrial Heritage sites preserved and open to the public in England pre-date the widespread use of this type of concrete (1920s to 1990s) its unlikely to be found in many industrial structures on display or in use. However, buildings added to industrial heritages as part of their conversion to visitor attractions in the later 20th century (such as interpretation centres or stores) might be affected.
If you are concerned, then the 20th Century Society’s guidance covers the history of RAAC, its relevance to different types of heritage, and potential solutions. Their guidance can be found here. Your local authority may also be able to provide advice, and the Local Government Association has now produced their own guidance which can be found here: https://www.local.gov.uk/topics/housing-and-planning/information-reinforced-autoclaved-aerated-concrete-raac?mc_cid=ec8acda62e&mc_eid=c1aec993c2
Industrial Heritage Networks 