CMU Lintel Damage 1

[reviest54]

I received an email with the attached photo from an architect concerning a CMU lintel that has cracked on the underside of the block (see attached photo). This is a solid grouted wall supporting a wood roof, should not have been a problem.

I must admit I have never seen a crack like this. The contractor is saying the cracking is from over vibrating.

Any thoughts?

Thanks.

 

[nackra]

is this in a zone subject to freezing?
If it is, then are there any weep holes? (didn't look like any from this angle)

 

[WARose]

Looks kind of like the cells could have been improperly/partially grouted. (or missing re-bar.) You've got a crack.....see if you can get a light on it and see inside the cell.

The temperature theory is a good one as well.

 

[charliealphabravo]

I don't see clear evidence of post-construction movement. There is unbroken mortar spanning the cracks and the face shells are all aligned. The face shell mortar is unbroken and the front/lower edge of the lintel is laser straight. Over-zealous use of a tremie/vibrator might be a reasonable place to start on cause. If the lintel/wall is grouted solid or reinforced and loads are nominal then it might be fine.

 

[reviest54]

Thanks for the responses. No temperature issues here. This was just installed a couple of weeks ago in Southern California.

 

[reviest54]

I meant to say a couple of months ago. I have a site visit later on in the week and will update the post if necessary.

Thanks again.

 

[WARose]

Let us know what you find (if anything). A lot of times people figure out a problem like this from a site visit and they don't follow up here.

 

[reviest54]

Will do.

 

[WARose]

Something else to consider to confirm the grout theory: bring something like wire that you can poke around in there (and bend so you can go into the cell at angles to see how big the cavities are (if there are any)).

Looks like the crack width(s) varies so you may want to bring light gauge stuff as well as the heavy (for serious poking).

 

[GC_Hopi]

My guess is that the bottom course was not properly grouted. Then it was damaged when they installed the overhead door/the static and dynamic loading of door. I am interested in that big hole in the fourth block. If it was from over vibrating then the mortar joints would have blown out and there would be grout in the cracks.

 

[reviest54]

GC Hopi: That was my original thought.

WARose: Good advice.

 

[masonrygeek]

Does it bother anybody that there isn't much mortar in the joints on the underside of the lintel? The mortar joints facing outwards appear to be nice and full and well-jointed, but the underside looks terrible. I wonder if they left the joints open so that grout would fill the openings between the block with the wood centering stopping any grout flow. When they grouted the masonry lintel the grout wasn't the right consistency and never filled the joints. And I wonder if they really did any vibration/consolidation...

 

[WARose]

That's a good point mg. Maybe they even tried to "grout" the first course with mortar. (I've seen it happen a few times.)

 

[reviest54]

MG: Thank you. Makes me worry about the rest of the structure. Not sure how high their lifts were, the grout mix design etc. A lot to unpack here.

 

[azcats]

Any chance the masons didn't have proper lintel blocks and field fabricated something that didn't work and/or left something hollow at the bottom?

 

[JAE]

Looks to me like this is due to possible lateral impact factors - as the overhead door slides down, the last, top panel snaps vertical at the end and there could be outward impact forces along the top, fracturing the block like that.

There's no evidence of lintel sag, or diagonal cracking in the face of the wall...so no overall movement but rather very localized distress.

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[Zambo]

That looks like a big span, how many metres is it? How many block courses is the lintel? Interesting to know if the design is on the engineer's drawings or a standard detail from the block supplier.

 

[hokie66]

reviest54 did say the whole wall is grouted, so the lintel height is the full height of the wall.

I vote with the contractor on this...the bottom of the lintel was pulled apart by the grouting/compaction. If that is the case, when you poke up into the crack, you should find solid grout.

 

[haynewp]

The cracks are also staggered at each block so the damage is more locally specific. I would vote damage during compaction too.

 

[reviest54]

This was a designed lintel and I have checked the design and it is satisfactory. This is a 14'-0" span. The entire wall and lintel was solid grouted.

I am going to the site this afternoon and will report my findings tomorrow.

Thank you everyone for your input.