Cracked CMUS's at Grouted Cells

[ToadJones]

I have a contractor that says he reinforced & grouted some 12'-0 CMU walls every two feet per the design drawings. He grouted the cells on a warm day in the Northeast early in January. The weather subsequently and quickly turned very cold.
The CMU walls cracked at every single reinforced cell line....every two feet.
I suspect, as does he, that the grout froze, or watered got in around the grout and froze and popped the CMUs.
There is no real debate on whether or not he is at fault; the question is now, how to fix ?
The cracks are hairline; hard to see in spot locations. The owner is fine with whatever can hide the cracks so long as they are not critical to structural integrity.
If not a structural problem (which I would say they are), is there an expoxy paint or some such that will suffice in hiding these cracks and not crack again with small movement?

How to tell if these are a major structural issue????

 

[chicopee]

We used an epoxy paint over the concrete floor of our paint storage area to seal cracks in order to contain spilled solvents so as to not contaminate the underground. Contact a major paint distributor such as Feldspar, Dupont or others for recommendation.

 

[BAretired]

Toad,

It depends on how cold it got after pouring the concrete. If it was just below zero, then thawed and stayed above zero for the remainder of the time, I don't think it has much effect on strength.

If the temperature was kept below freezing for two or three days, it is not likely that the concrete will regain its strength. Epoxy paint on the CMU will prevent water from entering the cracks and freezing again, but will not effect the strength gain of the concrete.

BA

 

[TXStructural]

I think you need to open up a few cells to investigate. Cut a square in the wall of the CMU over the grout and see if everything is bonded, and the extend of the cracking. Look at grout quality and block integrity. Hairline cracks in the CMU shouldn't reduce compressive strength significantly, but the underlying mechanism could have compromised the system significantly.

If this is a shear wall or in a region developing reinforcement, cracking could be an issue.

 

[Ron]

Agree with TXStructural...investigate further.

 

[ToadJones]

My biggest concern right away was, if water infiltration b/t the block and grout caused the expansion and cracking or if the grout froze, then the bond b/t the block and grout was lost.

I agree that he should cut a few areas to investigate.

If the CMU is bonded well to the grout, would you say the hairlines are not an issue?

The problem as I see it is, the cracks are in the direction of the reinforcing, so the section has lost depth, and now the strength of the wall laterally is almost entirely depending on the grout & bar.

Also, the wall is 12' tall and the cracks are at nearly every single reinforced cell line = every two feet. The cracks only propagate down about 4-5' from the top of the wall.
It makes me wonder if it didn't rain on the wall (uncovered) and have water seep between the grout & block then subsequently freeze and crack.

I guess the reason for the cracking is just curiosity ...the bottom line is that the blocks are cracked and if not a structural issue, the contractor must find a way to hide the unsightly cracks.