retrofitting column with vertical hairline crack 3

[Ca_87t]

This round column measuring 12 inches diameter (0.3 meter) has 8 pcs of 20mm rebar with 10mm spiral ties spaced 8 inches (0.20 meter) apart.

There is a vertical hairline cracks measuring about 1 meter. I'd like to know the following:

1. Usually what caused the vertical hairline crack?

2. Can the rebar inside rust if nothing is done to them?

3. Should carbon fiber be wrapped around it?

 

[oldestguy]

Suspect temperature effects, expansion and shrinkage. Appears to have differential exposure to elements.

 

[Ingenuity]

Probable that it is corrosion induced. Do some small invasive probes - remove cover concrete - and visually check the longitudinal and traverse reinforcing for corrosion.

What type of exposure is it - sub-tropical, exterior, within < 1 mile from coastal chlorides?

 

[Ca_87t]

The coastal is miles away.

It is exposed to rain. Can rain water get inside the hairline crack?

Our area is a seismic zone. Can any further seismic activity open it up so carbon fiber wrap around it is required? I think wrapping it with carbon fiber can totally prevent any spalling making it stronger than the original. But are the spiral ties in the sketch sufficient with 8 pcs of 20mm main longitudinal rebars?

 

[Agent666]

Are you sure it's not just a crack in the applied render?

 

[Ca_87t]

I don't want to chip the render or concrete as the whole column is only 1 foot diameter. Here is zoom of it. It doesn't look like just the render because the crack is discontinuous so unlikely.
Supposed the crack is up to deep inside. What kind of failure mode would occur. It's not a shear or diagonal failure.

 

[jayrod12]

If you think there needs to be a repair, then doing some small invasive chipping to determine the cause should be the least of your concerns.

 

[hokie66]

I think cracking of the finish is more likely than cracking of the concrete. But you will have to remove some to tell. Probably not a big structural issue.

 

[Ca_87t]

What if I chip 1/4 inch.. then 1/2 inch.. then 1 inch or 3 inches or more to inside.. then a lot of concrete would be lost.


To put carbon fiber to it. The surface simply has to be finished to smooth texture so the epoxy can hold.

 

[Agent666]

Carbon fibre is only generally used when you have a confinement issue not as a crack repair strategy. Like others have said, to repair and address the root cause you probably need to investigate what is going on, and if it turns out to be a durability issue establish if it is a carbonation issue, chloride ion ingress issue, some issue with the orginal workmanship, etc. If its just a crack with no underlying issue, then getting it injected is pretty easy, followed up by tidying up the render.

All concrete cracks (due to shrinkage/flexure), if the cracks are within the bounds of what is allowed considering durability provisions within your code of choice, then there is nothing to probably worry about unless you have signs of spalling that might indicate a corrosion issue.

 

[RHTPE]

The column shown is obviously not as-cast and has some sort of stucco-like coating. What is the coating? If it is a brittle cementitious or acrylic material the crack may just be in the coating material. Best you try to confirm that the crack is indeed in the underlying concrete.


Ralph
Structures Consulting
Northeast USA

 

[Ca_87t]

Ok. Which part is best to chip.. top, middle or bottom of the column for those who have tried chipping columns before?

 

[hokie66]

That would be the part which you can easily reach.

 

[NorthCivil]

A semi-educated opinion:

The column is coated in plaster. trying to diagnose a problem with the column behind is even more of a guessing game than identifying structural problems from the inside of a building via a crack in drywall. you need to clear away the plaster to really know whats happening.

My guess-timation is that the plaster coated column experiences regular wetting and drying on the external face, regular sun & associated temperature variations on the external face. The inside face is sheltered. These repeated weatherings has cause movement, which is why there is a vertical crack along the line between exposed and sheltered plaster.

I wouldnt give any opinion without tearing a good portion of the plaster off of the post.

 

[SlideRuleEra]

If the crack is determined to be in the concrete, not a coating, consider structural injection for crack repair. We did this on a structure in high seismic zone that had cracking worse than the photo.

http://www.SlideRuleEra.net

 

[bridgebuster]

I was thinking the same thing as SRE. We do this all the time on bridge rehab projects.

 

[BridgeSmith]

I'm with SRE and Bridgebuster - epoxy resin injection. That's what we do for bridge columns with cracks like that.

 

[Ca_87t]

We chipped off the surface, the crack is in the concrete and not the coating. See:

It is NOT even 1mm wide, just paper thin hairline crack.. how do you inject epoxy resin in paper thin gap? If not possible, how do you fix it?

 

[SlideRuleEra]

...NOT even 1mm wide, just paper thin hairline crack.. how do you inject epoxy resin in paper thin gap?

Sometimes I wonder why I even try to give members a complete answer...

on April 24, I made a post about your question...

in that post there is a link that opens a document...

the document outlines how this type repair is made...

Read... The... Document... All... Of... It.

http://www.SlideRuleEra.net

 

[Ingenuity]

Keep chipping...you have NOT determined the cause.

Crack injection of concrete cracks as fine as 0.005" (0.1 mm) are possible with the right plural-component pumps and low-viscosity resins.