I'm going to cast a 200 (depth) x 100 (height) mm section over 2.3m (length) this is a replacement stooled window cill in concrete. I'm thinking I should use some form of reinforcement. I am concerned about the premature failure of the conventional mild steel rebar so was thinking I would use some 304 stainless steel round bar. What kind of diameter would any of you guys suggest for this size section? I was thinking 1 x 16mm dia over the length......
Reinforcement bar - what size to use
- Thread starter vards01
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Is this a cill for a nuclear reactor? Stainless reinforcement is only used in highly specialised concrete like some areas around nuclear reactors. Use normal mild steel stuff. It's purpose is only to stop shrinkage cracking. Just ensure that you have at least 20mm cover to the rod(s).
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Reinforcement is usually used to give the concrete strength in tension, as standard it has very little so can't bridge over more than a few inches without support. Maybe rebar isn't even need for the window cill, something much thinner would be plenty?
The only reason for wanting to use stainless is to stop it blowing out from corrosion, over a period of time. For the sake of an extra £20 i think it is worth using a corrosion resistant material. Its going to be a lump to lift in place so would like to have something to prevent the fracture of the section also. On the cills I have seen cut it looks around 12 - 18mm standard mild steel rebar.
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Doggit
Redbar has ribs, and it's this that provides the strength, stainless steel bar won't have the ribs on it, so would be a waste. Think about making up a frame, and casting it in situ. Rebar is always open to the elements on site, and once encased in concrete doesn't rust any further because there's no air to oxidise the steel; as long as it's been made properly, and doesn't crack, then it'll be fine, but if it cracks, thats when it starts to rust and expands, so enhabces the crack.
I was going to lightly key the 16mm stainless with an angle grinder to provide the key as I had thought of this also. The standard rebar as you say is widely used and fine until the PH of concrete drops with age (this is what I have read) and then allows the steel to oxidise and then pops the concrete. You wont be casting a stooled cill insitu its not a constant section. I have made the mold now anyhow. Part of me is tempted to just stick the steel one in as its stocked in travis, but I'll kick myself 10 years down the line if it pops. You are talking £20 quid difference.
10 years? UK National Annex to BS EN 1990:2002 gives an indicative service life of 120 years. This is how they design significant structures like tunnels and bridges. Mix your concrete well, ensure good compaction without honeycombing and keep the cover >20mm and it'll last a long time.
PS. I thought that you were talking about stainless reinforcement, not just a sanded bar from B&Q. Anyway, don't bother.
PS. I thought that you were talking about stainless reinforcement, not just a sanded bar from B&Q. Anyway, don't bother.
I was going for 304st/st not b and q special. 120 years that sounds more like it, 10 years was obv a worst case.....You think 1 x 16mm will be enough?
If I knew who sold the stainless rebar locally obv I'd buy that not sod about with an angle grinder.
If I knew who sold the stainless rebar locally obv I'd buy that not sod about with an angle grinder.
No there is actually stainless steel reinforcement in the appropriate profile like this:-
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Talk about over-thinking...
Yes I had seen it.....i meant there is no where locally I can purchase it.No there is actually stainless steel reinforcement in the appropriate profile like this:-
To control cracking in a concrete window sill I’d either use 2 or 3 normal B8 or B10 bars or some D90 wrapping mesh. 25mm cover should be fine.
For good durability you’ll want a concrete mix with a low water to cement ratio thus reducing its permeability.
For good durability you’ll want a concrete mix with a low water to cement ratio thus reducing its permeability.
I've gone and brought a 16mm one now........the factory cills I had seen only had one.
I was thinking a 2ballast- 1sharp -1 cement mix on the dry side as you say.
The finished article will also be painted.
I was thinking a 2ballast- 1sharp -1 cement mix on the dry side as you say.
The finished article will also be painted.
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