Reinforced Autoclaved Aerated Concrete (RAAC) across the public sector in Scotland

Introduction

This report provides an update and overview of the discovery and assessment phase in respect of the presence of Reinforced Autoclaved Aerated Concrete across the public sector in Scotland.

The report sets out the background on RAAC itself and contains reference to various inspection and assessment work. It goes on to set out the action taken by the Scottish Government and wider public sector/partners in the discovery and assessment of RAAC including the establishment of the range of networks engaged with – or established – to support this work as it has been taken forward.

Reference is also made to those organisations, including those from the construction industry, offering guidance and advice on RAAC, such as its identification, assessment and appropriate management.

The conclusion of the report outlines continuing and next steps in terms of longer-term management plans demonstrating ongoing commitment to ensure all reasonable measures are taken to identify, mitigate and manage RAAC to the extent it is present in the public sector.

Reinforced Autoclaved Aerated Concrete (RAAC)

RAAC was a building material used in some buildings to form roof planks, wall panels, and sometimes floor planks, between the mid-1950s and mid-1990s. While use of RAAC stopped around this time in Britain, research from Loughborough University indicates that ‘RAAC is still manufactured and installed all over the world…’. For more information, read: Expert explainer: what is RAAC and why are people concerned. 

RAAC itself is a lightweight material that is formed by mixing together cement, very fine sand or pulverised fuel ash, lime and finely divided aluminium powder. The dry mix has water added and is mixed together, with the mix being placed in moulds (which have the reinforcement already in place) where the initial reactions take place when placed in an autoclave for 12 to 18 hours. The lime and aluminium react to form hydrogen gas bubbles. It is the gas bubbles that provide the lightweight aerated structure to the material. The material rises once the reactions take place and it begins to set.

Manufacturing of RAAC took place at several locations around the UK. This included a manufacturing plant in North Lanarkshire that used a trade-marked type of RAAC construction called Siporex (a product originally developed in Sweden).

While issues with RAAC have been known about for a number of years, the presence of RAAC in a building does not necessarily mean that the building is unsafe. If properly designed, manufactured, in good condition and with good bearing, RAAC installations are considered safe. However, where building owners have not carried out proper maintenance, the panels can creep and deflect over time, which can be exacerbated by failure to prevent water penetration.

It should also be noted that, although widely reported that RAAC has a lifespan of 30 years, The Institution of Structural Engineers (IStructE) considers such statements to be misleading with no specific data to support the claim. Research indicates that provided RAAC has been maintained correctly it should perform no differently to comparable materials.