Need Help Identifying a Concrete Crack 1

[XR250]

There is a hairline to 1/8” crack in this 5’ x 2’ x 18’ concrete pillar. The pillar is not load-]bearing, however, it is integrated into the foundation wall of the house. The homeowner noticed bubbling in the stucco, and had it removed for further investigation as is shown in the picture. The top of the pillar is stuccoed and there are some hairline cracks in it. To the right of the pillar is an upper basin and waterfall feature. No cracks were observed in the foundation wall from within the basement.
The house is 20 years old and the crack was only recently noticed.
I’m thinking that water may have gotten into the column from the top (rain) or from the side (water basin) thru a shrinkage crack and frozen. Could it also potentially be pent-up casting stresses that just decided to “let loose”? Seems like a big pour and the lateral rebar would be pretty important. I designed the wood framing for the house and my colleague did the concrete, but he has since passed, and I don’t have his records that far back.

Any thoughts?
Thanks!

 

[phamENG]

I agree some of the spalling may suggest freezing - or maybe the contractor who removed the stucco got a little aggressive with his grinder. How about corroded reinforcing? Any chance the water got in and starting rusting the center bar? That could cause a splitting failure in the face.

 

[dik]

Can you take a gentle 2" core down to the reinforcing to see if it's there and what the condition of it is. Stop coring when you reach the rebar, not when you've passed through it. It doesn't appear to be heavily loaded, and repair might just be cosmetic... a fiberglass 'bandaid' and new coating. With remedial stuff, you have to be careful... I've often encountered where the fix is worse. Concrete restrained by corner bars?

Plastic shrinkage from too high a slump?

Dik

 

[XR250]

I suppose the rebar could be corroded. If so, would it be reasonable to seal up the exterior faces as much as possible, do an epoxy injection on the crack and call it a day (for now)?
It is only an arch. feature and not carrying load other than its self weight.

Thanks

 

[r13]

Is this an ocean front building? If so, I think you need to thoroughly clean the crack before patching.

 

[Ingenuity]

If this was my home, before I would attempt any repair I would do a few probes over the vertical crack and part expose the rebar - say at 3 locations. Do a visual on the rebar condition (corrosion) then determine if rebar corrosion was the probable cause. If it was not, then patch the probes, seal/inject the cracks and re-apply stucco/finishes.

If the crack was due to rebar corrosion - without significant pitting to the bar - then consider sacrificial zinc anodes tied to the rebar and embedded in the concrete. Seal/inject cracks and apply finishes.

If corrosion is significant then more extensive rebar repairs may be warranted.

But, that is me - and this is not my home - so good luck.

 

[darthsoilsguy2]

seems like a good application for carbon fiber repair.... it will still likely be noticeable on the finish with a comparable feature right next to it. An approach could be... 1. Remove entire coating from face. 2 Grinding it down to inset the fiber so it is flush with concrete or.... stripe fiber to the entire side with a 12" stipe up the middle and 6" stripes on both sides to pad out. 3. working the crack for extra epoxy. 4. put the repair in per manufacturer directions. 5. reapply coating. The project seems too small to merit a mock-up for the coating, but you'll want the owner involved in that coating because it will never match perfectly and it isn't fair to 'demand perfect' from contractors either. Paying a contractor for a mobilization to do a mockup for a few square feet at ground level would be a good way to protect the contractor and the designer from aesthetic callbacks.

 

[XR250]

@R13 - 150 miles from the coast

@Ingenuity and dik,

I assume core at the crack as that would be the most likely position of the vertical rebar?

 

[JoelTXCive]

It appears that the stucco is applied directly to the pilaster. I do not see any lathe or bond breaking material.

When it is rebuilt, can the stucco be isolated from the concrete pilaster so that if it does crack again, it would not telegraph through? (i'm thinking a layer of 15# felt paper and then a metal lathe.)

After injecting the crack, you could re-stucco + paint (with elastomeric paint) the front face of both sides so that they match.

 

[EdStainless]

There are corrosion inhibitors that could be injected into the crack if you find that rebar corrosion is minimal to none. There are also conversion treatments that could be applied to more corroded rebar.
Are they sure that there is no chance of water entry further up the pilaster? Sealing is critical.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[XR250]

Thanks for the help. Sounds like the owner wants to inject it with epoxy, try to seal this thing up the best he can and talk to his stucco guy about possibly isolating the front system from the face the pilaster.

 

[LittleInch]

Did no one cotton onto the fact that the blue bit to the right of the pillar has been a running waterfall; / water feature for 20 years??

I'd say it's amazing it lasted this long.

Can't work out the detail at the top to see where the water interface was but if the re-bar isn't corroded it will be at some point.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

Yup, if rebar corrosion is the issue... check concrete cover to see if adequate... could also be plastic shrinkage if a really high slump concrete was used and concrete was restained at corners... dimensions are very small for shrinkage, though...

Odd that none of the other concrete has been affected.

Dik

 

[JoelTXCive]

Here's more fuel for the speculation fire:

It seems like you could get some really good temperature differentials between the top of the pilasters and the bottom.

The top appears to be exposed to direct sunlight; and the bottom looks like it stays shaded and nice & cool with the water.

I love the look of stucco, but it was my nemesis back in my homebuilding days. We would get warranty calls like clockwork about 2 years after closing for cracks.

 

[XR250]

Good stuff - thanks

 

[Compositepro]

The temperature cycling causing the cracking is a plausible theory. But I would say more likely due to the sun shining more on the side of the pilaster, which then gets suddenly cooled by turning on the waterfall, in the evening. The other pilaster (not cracked) appears to have a shaded side facing the waterfall. It appears that the top part that does not get wet, did not crack. Although this could also support corrosion as a cause.

I think a fiberglass/epoxy repair could work for this. Carbon fiber is often used for repairing concrete because glass can be weakened by caustic cement, but with epoxy coating I really cannot see this as an issue. Carbon is stiffer than fiberglass but I do not see this as an advantage here. Elongation is good for bridging cracks. Carbon and glass fibers have very similar tensile strength (~500 ksi). Carbon is three times stiffer.

Anodes on the rebar would only help if galvanic corrosion is the mechanism, rather than general corrosion in (probably chlorinated) water. Galvanic corrosion is unlikely.

 

[dold]

Seems like trying to repair this would just be a waste of money. It looks like this is just a purely architectural feature - non load bearing. Shoot some lath onto the face before re-stuccoing to minimize future stucco cracking and seal the joint. Epoxy injection seems overkill? Or am I missing something? But, if thats what the owner wants, by all means... Looks like it's not going to break their bank.