Rebar in 4" CMU 4

[FootNMouth]

Can you place vertical reinforcement in 4" masonry blocks? I was told that you can't but after getting my hands on some it looks like you could get one bar.

 

[Ingenuity]

The vertical rebar can be installed, but the grouting is near impossible for 4" block.

 

[CELinOttawa]

No. Despite the temptation, it cannot be done well enough to be reliable.

You CAN, however, post-tension a 100mm (4") block. It is then pressure grouted from the bottom... You need to use witness holes, and this is an expensive procedure only used for very specialised applications such as industrial overpressures.

 

[FootNMouth]

Thank you for the info.

 

[XR250]

Not reliable as CEL says, but could be used in a belts and suspenders approach. Will be much stranger than un-reinforced, just nothing you can put a number to.

 

[Jerehmy]

What if self-consolidating grout was used with vibration to ensure proper filling of the cavities? Is this more expensive than just increasing wall size?

 

[Duwe6]

How do you fit a vibrator head down the aligned holes in 4" block, said holes already having a bar in them? Before I would let something like this on my project, I would demand a demonstration section be built, cured, and scientifically destroyed.

Cheaper to just use 8"CMU, like these experts are trying to tell you.

M. Escher drew a bunch of things that cannot actually be built. You have to watch out for the physical limitations of your materials, especially constructability.

Good Judgement comes from experience; most experience is garnered from bouts of bad judgement. Try to use somebody else's bad judgement, your resume gets pretty bad if it is always your own bad judgement.

 

[Archie264]

For what it's worth I once heard a mason say that when grouting is specified he simply fills the cores with mortar as he goes. I'm not saying that's right; I'm just saying that absent direct oversight that could very well be what's done.

 

[Jerehmy]

Duwe6 - I was asking a question out of curiosity, I'm not the one designing a 4" masonry wall so you're comment "like these experts are trying to tell you" was uncalled for and unnecessary because I JUST entered the discussion.

Also, have you ever seen self consolidating grout/concrete? I've been at plants and I've seen it in use. It would have no problem filling the cores even without vibration based on what I've seen.

 

[concretemasonry]

If you want to grout properly, you NEVER use mortar but a true grout (8"-11" slump) to allow the grout to fill every void possible void and the CMU absorbs the excess water as it consolidates. Go slow and remember to top of after the consolidation if you depend to have a an axial load applied in bearing. While it is noble to use a 4"(100mm) block for wall thickness and details, 6" or 8" are superior in terms of cost and quality of construction. - An reinforced 4" wall will cost more than a 6" wall, that allows proper grouting techniques/procedures.

Unfortunately, few engineers really consider constructability and appearance and just arbitrarily specify a thickness and no more items such as strength, configuration (number of webs, web locations, etc.) based on some generic national minimums or configurations. Very often a "standard" 4" CMU cannot even be grouted because of the common core configurations.

Whatever CMU thickness you use, make sure the core configuration you specify is available for the thicknesses and bonding.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.