Throughout 1980’s there were many notable instances of Reinforced Autoclaved Aerated Concrete (RAAC) roof plank failures. It was thereafter identified that roof planks constructed of this form were highly likely to fail and resultantly such structures were either demolished or replaced as a result.

Autoclaved Aerated Concrete (AAC) is unlike standard dense concrete as it has no coarse aggregate. AAC is instead formed using fine aggregate along with chemical additions which act to create air entrainment bubbles before heat is applied to cure the element. AAC is a low-strength, lightweight concrete with minimal capacity for developing a bond with the embedded reinforcement.

AAC was typically used in two main forms; firstly, in lightweight masonry blocks and secondly, in structural units for roofs, floors and walls. AAC is reinforced to form structural units commonly known as RAAC. The lack of bond to the reinforcement means that protection against corrosion is provided by a bituminous or a cement latex coating which is applied to the reinforcement prior to casting the element.

Case studies have revealed a number of deficiencies as a result off the production of RAAC panels such as incorrect cover to the tension steel, high span to depth ratio and insufficient provision of transverse links. Further contributory factors to these failings were identified to be due to a failure in performance of roof membrane and rapid worsening of local corrosion of steel. Although a lot of buildings containing RAAC were demolished in the 1980’s, there are still a large number of buildings in the UK where RAAC panels are present. Therefore, it is essential for asset owners to understand if these RAAC panels are present and to investigate there condition. BRE Information papers have been produced to assist with the assessment of RAAC panels BRE IP07-02 & BRE IP10-96.

Empirical offer experienced engineers to undertake the necessary initial inspection for identification of RAAC and further investigatory works to identify if there are any concerns thus aiding asset owners with condition assessments. Using a combination of non-destructive testing, inspection, in-situ measurements, and limited investigation methods, Empirical ensure the required information is gathered to assess the serviceability of the RAAC panels.