what is the thinnest concrete panel one can reasonably form? 2

[NorthCivil]

I'm involved on a project where there is existing Glass-fibre reinforced cladding panels that are failing. rising up 15 odd levels on a building in the city. size of panels, about 3m x 1m (approx 3.5ft x 9ft)

we will be removing and replacing, the client hoping for something that looks the same. the look from the exterior is textured plaster, which has been applied around the building, over exterior concrete and GRC cladding panels alike.

client is pushing for these locally available aerated concrete panels. primarily because they are light and cheap. what these are, is aerated concrete, strength of 4MPa, 50-75mm thick, with a grid of steel reinforcement in the middle. the reinforcement is a grid of 3 or 4mm steel mesh in the centre. 150mm x 150mm grid. these get screw fixed back to the building, right through the panel

I've done my homework on these and im not too keen. on the lightweight concrete, as it is very porous. nor am i keen on the strength. also not keen on the reinforcement in the panels, which is galvanized steel, but because it is so thin with porous concrete, will surely be getting attacked. worth mentioning we are within 300m to the sea.

i have proposed to the client maybe we can form our own panels of ordinary 30mpa concrete, using stainless steel reinforcement. likely a 150x150mesh of the same size. with potentially some extra reinforcement near where we do anchor points. anchors will likely be the same, screw fixings right through the panel. M8 epoxy anchors or similar.

wondering what is a reasonable minimum thickness to target? does anyone here have experience casting very slim concrete, and have any tips to offer?

because we will be laying these panels over battens and have the opportunity to connect back to building at regular intervals, the panels will be under minimum stress. the real concern is what is a minimum thickness of concrete that can remain reliably cohesive, as it hangs 200ft above pedestrians in the city?

 

[Greenalleycat]

At least here in NZ, aerated concrete panels are super common - surprised you can't find a proprietary product that suits your needs
It looks like the systems here use unreinforced concrete with a fibreglass mesh embedded in the plaster - no steel

I would be less keen on your suggestion as I think the thickness would be realistically governed on cover requirements given your distance to the sea
If you really wanted to do it I'd be using a higher strength concrete (40MPa+) to densify it as much as possible against salt attack
Also, thermal issues could be quite significant
If you're in a seismic area you will be adding significant mass to the building
Thinking about it, this could even be very important for gravity loads too - will this mass be significant?

Overall, this way you end up taking liability for both structural and architectural constraints - is that really worth it compared to finding a suitable proprietary system?

 

[Brad805]

50mm panels will not remain anywhere near flat at those dimensions.

 

[NorthCivil]

hi Greenalley.

aereated concrete panels are lovely, but for the reasons i described, not fit to be hanging 200ft above a sidewalk in the city. some backing research at the links below.

the cladding does not cover the entire building, so the mass wouldnt be overly significant. there is a structural engineer involved as well looking at the building so they would review and need clear any modifications to mass.

salt attack issues should be negligable if using stainless steel reinforcement.

https://www.spicersurveys.com/blog/...us#:~:text=Introduction,to be around 30 years

https://hamptonjones.com/latest/how...dding-panels-constructed-of-aerated-concrete/

 

[dik]

I think the thin panels (maybe thicker than 2") would work well. It depends on the loading condition... not likely good for hurricanes or seismic loading. Safe, secure connections would be critical. If at height, 2" thick or 10" thick doesn't make any difference if not secured. If on the edges of buildings, they can be subjected to significant wind forces.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

Just a rough figure, (precast panels, about 3m x 1m , spans 3m , btw floor to floor ) for solid pc ; 125-150 mm, with vertical ribs ; 100 mm .

The thickness should be chosen with calculation ( considering ;concrete placement, min. cover , stripping , lifting , transport , erection and applicable wind etc..)

I would consider new Glass-fibre reinforced cladding panels (manufactured by a reputable company )..


My opinion..








I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[StrucPatholgst]

What about SHERA or Nichiha panels. They are super light, very thin. Not sure if there's a height limit for them, though.

 

[NorthCivil]

Shera, Nichita, really should never be installed to heights.

they are compressed fibre cement sheet. the fibres, being wood fibres.

when screws penetrate these panels, it creates a breach in the matrix, allowing the porous wood fibres to absorb moisture and swell. leading to cracking and deterioration, starting at the fixing point.

fine for ground level stuff... not so fine hanging 200ft in the air.

thanks for the input Strucpath

 

[XR250]

ChatGPT much?