Self Consolidating Concrete

[ajk1]

1. Does self consolidating concrete have more shrinkage than a regular mix of the same strength and w/cm ratio?

2. Is self consolidating concrete available in CSA Exposure classification C-1; that is with a w/cm=0.40 and resistance to chloride penetration (56 day rapid chloride permeability in index of not greater than 1500 coulombs) and freeze-thaw resistance?

3. Is self consolidating concrete available in CSA Exposure classification F-1?

4. If I specify stainless steel rebar, is it sufficient to specify concrete that has freeze-thaw resistance (i.e. F-1) but not the degree of chloride resistance required by CSA C-1? It seems to me that with stainless steel rebar, that F-1 should suffice. The reason for the rebar is that I am extending an existing step tread from 11.5" to 14.25" and to do this I am doweling the 2.75" wide extension piece into the vertical face of the existing concrete riser. Note that this is in the exterior concrete landscape walkway so the width of the 2.75" wide extension is 30 feet to match the existing walkway and step. The rebar is to control crack width in the new 2.75" wide x 30 foot long piece of concrete.

 

[TehMightyEngineer]

4. It seems that at 2.75" wide a rebar dowel isn't going to be developed properly in the extension piece. Sounds like you would be better off with stainless powder actuated fasteners embeded in the surface you're going to pour against.

Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)

 

[ajk1]

I know that, but it does not have to be developed very much. My calculation is that they could be spaced more than 4 feet on centres, but I am spacing them 12" on centres so the force in them is tiny. An alternative is demolish the existing step and start all over, but that would be much more expensive, although I may sketch that up to and have it quoted. Thanks for responding.

 

[jayrod12]

Haven't we already had the debate about adding the 2.75" of concrete?

Might be useful to link it here so that others don't rehash the same issues and stick to your self consolidating concrete questions.

1. No idea, the local redi-mix supplier is better capable of answering that.
2. See above
3. Same
4. The way it has been explained to me the chloride can have a impact (albeit small) on the molecular structure of the concrete. So if C-1 concrete is available that's what I would be using. I'd also be extremely concerned about water freezing in the cold joint. But as I said this has been hashed out before I believe in an earlier thread.

Why do you need self consolidating? It the contractor too lazy to run a vibrator while he's filling the form and finishing the top? That way you could get the concrete you want without worrying about self consolidation.

 

[ajk1]

Thanks Jayrod. The local contractor's quality control manager, who is generally quite knowledgeable, did not know the answers, but said that he would proceed to look into it and get back, so in the meantime I went to the next step and posted the questions here. The reason for preferring self consolidating concrete is that it produces a better surface finish, with many fewer bug holes etc. This is the grand entrance walkway to a public building, so surface finish is important, but not at the expense of diminished performance. Do you have a reference publication that I can read up on how the chloride negatively affects the concrete itself? I am interested not only for this project but also in general, because it goes to the important question of whether C-1 concrete has to be used when the rebar is stainless steel.

 

[hokie66]

2.75" of concrete, whether 'self consolidating' or not, is going to crack. If this is a monumental stair, find another solution.

 

[CELinOttawa]

Our detail, for major repair works, is to provide heavy cover (read 2" plus) and embed either SS mesh, pulltruded GFRP mesh/light grating, or (rarely) heavy full HDG mesh in the cover... Yes, technically this is no longer "clear" cover, but it provides excellent corrosion protection AND is very unlikely to crack. I've also been very tempted to try poly fibre admix, but I'm not keen to do so on a large job and face the flak if it all went sideways.