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Minimum hole size in bottom of CMU U-block for vertical rebar?
4

Minimum hole size in bottom of CMU U-block for vertical rebar?

Minimum hole size in bottom of CMU U-block for vertical rebar?

(OP)
Is there any document or standard that recommends or requires a minimum hole size in the bottom of a CMU U-block for vertical rebar? Obviously, it needs to be big enough for continuous vertical rebar and grout to pass through. Seems like it would also depend on if you were trying to fill cells underneath the U-block or just the U-block.

RE: Minimum hole size in bottom of CMU U-block for vertical rebar?

2
If you need to fill holes underneath the U-block, don't use a U-block. Use an open lintel block instead.

BA

RE: Minimum hole size in bottom of CMU U-block for vertical rebar?

(OP)
In my area, it is common to have a continuous U-block at the top of the wall. So for example, if the wall design calls for #5 bars at 48 inches on center, then they would make a hole in the bottom of the u-block at 48 inches on center so the U-block can be set over the vertical reinforcement and grout can flow through a fill the cells during the final pour.

RE: Minimum hole size in bottom of CMU U-block for vertical rebar?

Up to the size of the core hole in the masonry below.

RE: Minimum hole size in bottom of CMU U-block for vertical rebar?

Agreed. What is the difference between coring a 3" or 5" opening. Also agreed, a U-block wouldn't be preferable. And finally, depending on the code you would need 1.5 times the maximum aggregate size as clearance to allow for consolidation but this would not work for high lift grouting.

RE: Minimum hole size in bottom of CMU U-block for vertical rebar?

2
The minimum size of a cell that is to be grouted can be found in the TMS 402/602 code and specification (previously ACI 530/530.1). In the 2013 version, see Table 7 on p. S-74. The size of the cell will dictate how high you can grout the wall. The smallest cell in the table is 1 1/2" x 3" when using coarse grout.

As per this question, why are you using U-block at the top of a wall? U-block are usually just used at lintels and other areas where there is an opening below that course. In the top or middle of a wall you should be specifying a bond beam block that have regular vertical cells and then webs that are either precut to receive the horizontal rebar or have knock-out webs that the mason actually knocks out with a hammer to place the rebar. Using a bond beam block ensures that the grout flows both vertically AND horizontally. See NCMA TEK 2-1B for a figure showing what a bond beam block looks like: http://ncma-br.org/pdfs/127/TEK%2002-01B.pdf.

If the mason doesn't know what a bond beam block is, you may want to look for another mason...

RE: Minimum hole size in bottom of CMU U-block for vertical rebar?

(OP)
Thanks masonrygeek. That's exactly what I was looking for.

I don't see the bond beams commonly used in my area, but will investigate further.

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