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CMU wall reinforcing and grouting height
2

CMU wall reinforcing and grouting height

CMU wall reinforcing and grouting height

(OP)
I talked to someone at SMI rebar who said that walls 24' high or so are being specified with continuous rebar more often (no splices allowed).
I am somewhat perplexed as to how this will work. Where I am, usually low lift grouting and 48 bar diameter splices for the wall reinforcing is what I have seen used.

I know that nobody is going to thread the blocks over the top of the reinforcing as the wall is built. Therefore, the only option I see is to pour from 24', which would seem to cause a lot of voids in the grout as you go down the wall.

1)Is this actually being done? And if so, wouldn't
  cleanouts be required going up the wall
  vertically?
2)How can the bottom lifts be effectively consolidated from
  20' above?
3)How could you possibly tell what the final position of
  the rebar would be in the wall towards the bottom of the
  pour?

RE: CMU wall reinforcing and grouting height

Haynewp:
The easy one first:
There are patented devices for holding rebar in place in the cells of the cmu - not cheap though. Also, if you use "Ivany" block, the horizontal reinforcing effectively holds the vertical rebar in place, but not in the centre of the cell.

Certainly, the Code requires cleanouts for high lift grouting. The Code allows a maximum grout pour height of 24 feet assuming a minimum 3inch width of grout space. See Table 7 in the ACI 530 Specs. However, the maximum lift height is limited to 5 feet. It is unclear from the Spec, if cleanouts are required at the bottom of each successive lift.

Hope this helps.

RE: CMU wall reinforcing and grouting height

(OP)
Thanks, I also found the 24' in the code, I guess this kind of justifies it.

It just seems to me like it would be difficult handling a 24' piece of rebar and placing it down into each cell. But I guess some engineers are worried that splicing is not being done properly so continuous bars are being specified.

RE: CMU wall reinforcing and grouting height

This is excessive handling of the block.  Masons are expensive and I am sure there is a considerable up charge for building the wall in this manner.  Could the face shell be removed at the cells where the rebar is and then grouted back in?

RE: CMU wall reinforcing and grouting height

They make open ended block for your situation.  The standard has one open end, but there are also blocks with both ends open (think of an "H").

RE: CMU wall reinforcing and grouting height

I agree with SperlingPE, this is excessive.  Just because the code allows 24' continous rebar doesn't mean you should use it.  How about the case where they are calling out #7, #8, and #9 rebar, how do you fit those in the wall?  You need a crane to lift them!  Your design has to be buildable!
 
The code allows rebar to be spliced and even installing rebar in adjacent grouted cells untied can be used as an approved "splice"!

If the rebar spacers are installed to hold the bars in the center of the cell, how do you get the grout past the spacer and insure continous grouting?

We have to make these designs practical and buildable.  Using short lengths of rebar, splicing and grouting as you go up the wall is the way to go IMHO.

Talk to some good mason contractors, they have to put this stuff in the wall, they should have some good ideas on what works and what doesn't.  Of course, all of their thoughts on the subject may not be printable, but the good contractors know how to do it economically, if the designers would only listen.

RE: CMU wall reinforcing and grouting height

(OP)
   For an update, I spoke with someone at the International Masonry Institute on this. He said this method is done all the time out West. They lay the block all the way to 24', thread down the one long reinforcing bar, have positioners (as mentioned earlier in this thread) to hold the bar going 10' max vertically up the wall, then pour the lifts. (All grout is being introduced from the 24' elevation.) With new vibrating equipment that somehow attaches to the rebar, consolidation is not a problem.

He said even large bars #7,#8 can be placed this manner without a problem. I also asked if voids in the grout would be a problem and he said they would not be as long as the grout meets Code requirements for the pour height.

He suggested doing it this way because it separates groups completely, block layers, reinforcement placers, grouters.

The whole thing is somewhat fascinating to me. I would like to get a mason contractor's opinion on it.

RE: CMU wall reinforcing and grouting height

I just recieved a copy of the "Masonry Designers' Guide", by The Masonry Society, 3rd Edition.  I'm just getting into it, it looks really good with lots of examples and it comes with a CD too. You can check out their website at info@masonrysociety.org

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