RAAC, or reinforced autoclaved aerated concrete, is a lightweight material that was commonly used in construction between the 1950s and 1990s. It served as an alternative to traditional concrete, offering cost and time-saving benefits. RAAC is characterized by its aerated or "bubbly" texture, like an Aero chocolate bar. However, it has a shorter lifespan of around 30 years and is less durable compared to standard concrete.