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I have worked in the building trade as a much younger person in the 80's. I have a fair grasp of physics and chemistry. I consider myself to be halfway intelligent around most issues with buildings. I never built anything with RAAC.
I actually found this information much worse than the opinion I had before it. I wasn't aware of the sliding due to heat, or the extra stresses caused by bad fitment in the first place. I only found out last night that water makes the material crumbly (literally like the crumble on apple crumble). This really is a can of worms. I can only see this causing an accident. I am hoping they have removed all from working under this type of building material.
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.
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.
Sorry but that is not the interpretation I got.
The rusting of the rebar causes expansion. Because aac has the air to absorbed that expansion. The rebar done not have the compressive protection of the concrete to prevent 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.