Comment on The Ugly Truth About Reinforced Aerated Autoclaved Concrete (RAAC)
tal@kbin.social 9 months agoI only found out last night that water makes the material crumbly (literally like the crumble on apple crumble).
I don't think that the issue is actually primarily the concrete weakening when exposed to water -- which does apparently happen -- but rather that the rebar internal to the concrete rusts.
You'll notice that nobody is complaining about "AAC" -- aerated autoclaved concrete -- but specifically reinforced aerated autoclaved concrete. The difference is the use of the rebar.
Granted, RAAC is probably used in places where structural strength is more important -- I don't know if a non-reinforced wall crumbling is as bad as a ceiling that's above someone's head.
The speaker in the video highlighted a new angle that I haven't seen before that I think is notable -- that specifically with RAAC, it's hard to tell if the rebar has been suffering from rust internally, because it apparently doesn't split the way regular reinforced concrete does.
Combine that with the fact that RAAC is particularly prone to rust damage to the rebar, and you've got a situation that theoretically shouldn't come up if the substance is protected from water, but if it does happen is prone to problems, is hard to diagnose, and has a catastrophic failure mode.
Syldon@feddit.uk 9 months ago
I am not an expert.
The guy in the video explained that the bar in the collapsed school was not rusted. The concrete had weakened or it was placed too close to the edge. This resulted in the bar being bent over at the ends. It seems the concrete is prone to failure in a few different ways. All of which stem from water damage from leaking above.
HumanPenguin@feddit.uk 9 months ago
Sorry but that is not the interpretation I got.
The rusting of the rear causes expansion. Because aac has the air to absorbed that expansion. The rear done not have the compressive protection of the concrete to preve t the bend. With non aerated concrete. When this happens it is obvious as the concrete collapses rather then moves aside.
The lack of compressive resistance above the rebar is what allowed it to bent.