Reinforced Autoclaved Aerated Concrete

Navigating the Potential Hazards of Reinforced Autoclaved Aerated Concrete in Building Construction:Navigating the Potential Hazards of Reinforced Autoclaved Aerated Concrete in Building Construction:

September 12, 2023 News

In May of this year, we reported on a concerning incident involving the collapse of a school roof, shedding light on the risks associated with Reinforced Autoclaved Aerated Concrete (RAAC) planks in construction. The Standing Committee on Structural Safety (SCOSS) had issued a warning, underlining the inherent weaknesses of these concrete planks and the urgency of addressing the issue.

At JMS Engineers, we have been proactively addressing these concerns for several years. Leveraging our expertise and dedicated efforts, we’ve been actively identifying and managing RAAC in schools, contributing significantly to the creation of safe learning environments for future generations.

In light of recent events, we would like to delve into the findings of the investigation and emphasise the risks tied to RAAC:

  • Weaknesses of RAAC Planks: The investigation found that the school roof’s collapse occurred suddenly, with little warning. A similar near-failure occurred in 2019 in a retail unit using the same type of concrete planks. RAAC planks, popular in construction from the 1960s to the 1980s, are notably weaker than traditional concrete due to their manufacturing process.
  • Lifespan and Replacement Recommendations: RAAC planks have an estimated lifespan of around 30 years, prompting SCOSS to recommend replacing all planks installed before 1980. This precautionary measure aims to mitigate the risks associated with structural deficiencies in older RAAC planks.
  • Previous Failures and Concerns: The report highlights previous failures in buildings with RAAC planks, particularly those from the mid-1960s. Many structures had to be demolished as a result. Key deficiencies included incorrect tension steel cover, high span-to-depth ratios, insufficient crossbars for anchorage, roof membrane performance failures, and localized steel corrosion.
  • Recent Issues and Effects: Recent concerns involve rusting reinforcement, leading to cracking and spalling of the AAC cover. Moisture and temperature fluctuations are believed to contribute to the cracking. Excessive deflections, independent behaviour of floor and roof planks, and inadequate structural integration have also been observed. These deflections have led to water ponding, increased roof loading, and reinforcing corrosion due to water penetration.
  • Risk Assessment and Remediation: The investigation of the 2018 collapse identified shear cracking near a support and potential indications of insufficient tension reinforcement. The report advises conducting risk assessments of structures built with RAAC planks and considering discontinuing the use of spaces underneath until strengthening or replacement measures are implemented.

The school roof collapse earlier this year highlighted the inherent risks of RAAC planks, as identified through investigations and previous failures. Immediate action is imperative to ensure the safety and longevity of buildings constructed with RAAC. Building owners and authorities should conduct risk assessments and implement necessary strengthening or replacement measures to mitigate potential hazards associated with RAAC planks.

Recognising these risks and the need for proactive assessment, JMS has played a leading role in raising awareness and conducting thorough inspections of school buildings. Our team of specialised structural engineers possesses the expertise to accurately identify RAAC and assess its condition.

Our involvement extends beyond identification and assessment. We collaborate with stakeholders to develop effective management and remediation strategies. By combining our structural engineering expertise with an understanding of RAAC’s weaknesses, JMS Engineers provide valuable insights and guidance to address RAAC-related risks in school buildings.

JMS Engineers has become a leading authority in identifying and assessing RAAC in school buildings. Our comprehensive approach and expertise are vital in mitigating potential risks associated with RAAC, ensuring the safety and wellbeing of occupants. Partnering with organisations like JMS Engineers enables responsible bodies to address the challenges posed by RAAC and take necessary steps to ensure the longevity and structural integrity of school buildings.

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