![]() The raw materials are cement, blast furnace slag, pulverised fuel ash or silica flour, and these are mixed with water and aluminium powder. In its most common form, it is used in the construction of lightweight thermal blocks. So although there is no central register of buildings containing RAAC, owners, local authorities, health trusts and education authorities must take steps to determine where such planks are being used so the risks can be mitigated.Īutoclaved aerated concrete (AAC) was developed in Sweden in the 1920s and introduced to the UK in the late 1950s. SCOSS also mentioned the discovery of water-related damage and spalling to the roof of a retail premises, while other reports have referred to evidence of corroded steel reinforcement resulting from moisture ingress. ![]() While the two are not necessarily related – the planks may already have been restrained – re-roofing with a darker material could have resulted in more expansion as this will absorb more infrared light, thus creating a greater degree of bowing. The roof covering had been replaced, and it was thought that thermal effects could also have contributed to the failure because bowing or deflection can be caused by restraint at the ends of planks, which prevents thermal expansion. The SCOSS report notes that there was evidence of shear cracking adjacent to a support in the school building, as well as possible indications of tension reinforcement stopping short of it. In May, the Standing Committee on Structural Safety (SCOSS) issued an alert about the collapse of a school roof last year (bit.ly/SCOSSraacfail), an alert taken up in advice from the Local Government Association. Click here to read the full article.Įxcessive deflections and transverse cracking were thought to be a key warning sign of failure in reinforced autoclaved aerated concrete (RAAC), but recent investigation has shown a much more serious risk of sudden failure. So how can surveyors tell whether the material has been used for construction and identify the warning signs?Īrticle published in RICS Journal. ![]() By Trevor Rushton, Director The potential for sudden failure of reinforced autoclaved aerated concrete planks has been highlighted recently. ![]()
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