4 ms·

RAAC: Public buildings at risk from concrete failure, experts warn

• ggm 3y ago
  I haven't yet seen a reason behind the high failure rate. I'm trying to think of reasons: * microcracks which in classic pre stressed (or not) reinforced concrete are contained by the rebar. * thermal expansion and contraction effects over time. * unexpected loads not predicted by the engineering models used to dimension the material. * embrittlement from ageing, although many forms of concrete age by getting stronger. * side effects of the surfactants added to aide foaming. * side effect of autoclaving.
  • zeristor 3y ago
    If not protected from water water can penetrate and rust the steel rebar.
    • ggm 3y ago
      I think there's significantly less if not no rebar in this stuff. Also aren't some rebar uses are said to get stronger with small amounts of rust causing expansion and locking/tightening?
• zeristor 3y ago
  “The material is liable to fail without visible deterioration or warning.” https://en.wikipedia.org/wiki/Reinforced_autoclaved_aerated_concrete https://en.wikipedia.org/wiki/Reinforced_autoclaved_aerated_...
• zeristor 3y ago
  ““It is RAAC from the 1950s, 60s and 70s that is of main concern, especially if it has not been adequately maintained. RAAC examples have been found with bearings (supports) which aren’t big enough, and RAAC with the steel reinforcement in the wrong place, both of which can have structural implications. Prolonged water ingress (not uncommon on old flat roofs) can also lead to deterioration.” https://www.lboro.ac.uk/news-events/news/2023/march/reinforced-autoclaved-aerated--concrete-raac/ https://www.lboro.ac.uk/news-events/news/2023/march/reinforc...