Grouting deep masonry beam 4

[enginerding]

I have a project with a 40" deep (5 courses) reinforced masonry beam. The mason is proposing to build this and grout this one course at a time. He would build it like 5 bond beams on top of each other. I cannot find any notes in ACI 530 regarding grouting beams in multiple separate pours. Is this allowed? Am I crazy for expecting this to be poured together to avoid "cold joints" through the depth of the beam?

 

[FoxSE14]

That's a deep beam. Do you have shear reinforcing (vertical bars) in the beam? If so, there will be some resistance to slip between the cold joints, though I'd be concerned about obtaining proper development length beyond the extreme top/bottom cold joints. Hook the vertical bars? I do not get into new masonry construction too often, so I am also curious to hear what others say.

 

[KootK]

I'd be inclined to let it roll. Every head and bed joint in masonry is really a cold joint. It never seems to bother us for shear in walls loaded transversely or in plane. Even where wall cores are solid grouted, that is generally done in lifts. My opinion is that the relatively low shear values used for masonry design already have the cold joint business baked in.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[concretemasonry]

It sounds like the mason is using the wrong block shapes OR they are not available from his supplier. There are various types of block made in most markets that has vertical webs that align, so the grout cells line up perfectly. I hope he is not planning to use mortar instead of real grout.

Normally, for large openings (like doors on a high-walled industrial location or gymnasium). The proper way is to use conventional bond beams (closed bottom) and block that allows any vertical horizontal steel to be placed as the units are laid and the wall grouted. This pushes a smart contractor towards this type of construction and promotes the use of plant mixed grout.

It is best to have some sort of detail or notes on the drawings to guide the contractors.

Dick

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

 

[hokie66]

In a reinforced block beam the face shells both serve as part of the concrete, and as the formwork. You want as little block and mortar as possible, and as much grout. If you do it the contractor's way, you just have 5 shallow beams, one on top of the other. I would require the beam to be built with H blocks, and grouted all at one time. But then, I rarely deal with concrete masonry walls that are not completely filled.

 

[KootK]

This is the situation here above the lintel course, right? Just without the metal lath?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

KootK,
I think you would use a lintel block with a closed bottom, as concrete masonry suggested, for the first course of the deep beam. The other courses could be knock out blocks as depicted on the right in your diagram. These are not "standard" blocks, which would require sawing the webs.

 

[KootK]

KootK, I think you would use a lintel block with a closed bottom, as concrete masonry suggested, for the first course of the deep beam.

This is the situation here above the lintel course, right? Just without the metal lath?

Don't mess with Canada.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[enginerding]

Thanks all for your input. It seems like we are split on whether to grout at once or one cell at a time. Maybe I will follow Fox's advice with the shear reinforcement so even if he is insistent on separate pours, we still have steel tying it all together. I will also follow up with the mason to see what types of blocks he will be using. I was under the impression (maybe incorrectly) that he would use 5 courses of closed bottom blocks one atop the other like 5 separate beams stacked. Maybe he will use the knockout blocks.

Thanks again!

 

[FoxSE14]

*Nod toward Canada*

You'll have to look at the geometry to ensure it fits, but I may even consider spec'ing 180-deg hooks at the top and bottom of the vertical bars to force engagement with your horizontal bars in the highest and lowest course.

 

[jayrod12]

Always 180 degree hooks on stirrups in masonry beams. I'm surprised you need a 40" deep beam without stirrups already.

I wold be specifying knock out blocks for everything but the bottom course, it can be a standard lintel block. As a happy medium with the contractor I would likely be comfortable with him doing it in 2 lifts, say 3 courses the first grouting, and 2 on the second. I would not allow him to use 5 layers of lintel blocks.

 

[concretemasonry]

hokie -

In many or most areas, the "knock-out" blocks are very very common. There are also block that are delivered and made without the upper 1/3 or 2/3 of the webs. I work for a company that sold manufacturing equipment to the concrete products industry domestically and internationally and we had a "library" of configurations that were common. In some markets the block were supplied with the top of the webs not knocked out because contractors could use the knocked out section to plug the cores, eliminating the mesh and handling/disposal.

The block producer I worked for for 20 years carried the knock-out units in stock for both plain face block and for split face architectural block configurations. We also made these configurations in higher strength block.

Check what is possible in the area you are designing for. - It is a big world.

enginerding -

The grouting of these deep masonry beams with the knock-out units is very similar to the grouting of an ordinary reinforced grouted masonry wall as far as procedure, lifts and and topping off to account for normal absorption of the excess water needed for a usable grout mix. For 5 courses, there would be no need to waiting, but it would be prudent to top off the last course after the consolidation to provide a smooth top better bearing for anything that is set on the walls. The concept of using 5 individual courses of solid bottom block would produce and inferior wall.

Dick

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

 

[hokie66]

concretemasonry,

Not sure why you directed that comment at me. I tried to make the same points as you did. Maybe it is in the translation...

 

[dhengr]

Dick:
Isn’t there also a “H” shaped block which has a center cross shell, but no end cross shells, which opens up the cores a bit, and doesn’t make the head joint area so tough to grout full? Those poorly filled head joint areas would be particularly bad in a deep beam action. The 5 courses of 8" bond beam block is an awful idea. The bond at each horiz. joint is not very good in terms of transmitting horiz. shear, and it is very difficult to get any vert. shear reinf’g. from top to bottom. It’s akin to claiming that 5-2x6's stacked atop each other, with no glue, makes a laminated wood beam. The individual 2x6's slide past each other when the deep beam tries to work, no hoirz. shear strength, no shear flow tying the pieces together to form the deep beam. The filled/grouted vert. cores and vert. reinf. serve this same function, tying the deep beam together over its depth, and providing a good compression block at the top. I would make the bot. course a 16" deep lintel block, set the rebar (horiz. and vert.), and grout it to within an inch or so of the top, leaving the grout fill rough. Set the next 3 courses of “H” blk. being careful to minimize mortar dropping, or removing them, set some top reinf’g., then grout the top 3 courses.

 

[hokie66]

dhengr,
I did suggest H blocks in my first post. Where I am, we tend to use them extensively when you want full grouting. Not sure about availability where the OP works, but H blocks should be a standard shape in reinforced concrete masonry.

 

[dhengr]

Hokie:
Yup... I thought I had read that in this thread, but then I couldn’t find it. Then you also said a fair share of what I repeated, but in few words. See how good I listen, learn and mimic?

 

[Archie264]

These "H blocks" are not overly fragile for workability purposes, then? I would have assumed they would be but that would have been just that: an assumption.

 

[FoxSE14]

Weekend is here - worry about H-blocks, knockouts, and the like on Monday!!

 

[Archie264]

Good point. Cheers!

 

[concretemasonry]

hokie -

I guess there may have been a difference of terms. Every marketplace/area has different terms. There is a divergence of the description for a block with 2 face shells and one cross web - In some areas, it is an "H" block and in other areas, while it is an "I" block, but just depends on how you orient it.

We made the 8x8x16 with two webs at 8" on center in both knock-out webs AND some with the top 2/3 of the webs not existing, because of the contractor and engineers requests.

All special units may have problems meeting the ASTM C90 requirements for structural, especially those with reduced web heights. - This has happened numerous times when we wrote the ASTM C90 standard that has a requirement for the "equivalent web thickness per liner dimension" of the unit. Fortunately, that can be resolved if the wall is partially reinforced.

In the real world, all block actually have a top and bottom and it is preferred to lay the preferred block with the top of the face shell that usually has a flair (extra 1/4") to make the unit easier to handle and spread a good uniform mortar bed with minimum mortar droppings in cores that are not good for grouting. - This is often requested by engineers and contractors.

Keep in mind the strength of the mortar and grout have minimal effect on the wall strength of the actual wall. - I have see engineers place a maximum on the grout strength to insure stress distribution through the wall that reflects the code and specifications for tall masonry walls (over 10' or so).

Cheers!!!



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