Structural performance of aged Reinforced Autoclaved Aerated Concrete (RAAC) roof panels

Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight, aerated cementitious material with no coarse aggregate, hence the material properties and structural behavior vary significantly compared with “traditional” reinforced concrete. It was a popular form of precast concrete panelized construction in the 1970s, especially in critical infrastructure such as hospitals, schools, and government buildings, and many of these structures are now at the end of their design life.

Although the quality of contemporary RAAC precast elements and structures is considered to be good, concerns exist regarding the durability, serviceability and structural reliability of 40–50 year old RAAC panels still in service.

Ongoing survey regimes and preliminary site observations and investigations of multiples structures in the United Kingdom have revealed significant problems in a small number of panels such as excessive cracking and deflection, insufficient cover, and reinforcement that is corroding and/or incorrectly placed.

This paper therefore presents data on the structural performance and integrity of aged RAAC panels from the 1960s and 70s still in service in the United Kingdom, and presents the outcomes of the most significant and largest research project in the United Kingdom in the last 10 years, which investigated the material properties, structural performance, and monitoring strategies of aged RAAC panels. Structural testing on full scale panels in the laboratory and in situ have been conducted, together with petrographical examination and computational finite element modeling of RAAC panels form different structures and locations around the United Kingdom.

The research has developed considerable new knowledge and understanding regarding the structural and material performance of aged RAAC panels and their associated failure modes, which will have significant implications for the repair, monitoring and management of these national critical infrastructure.