Problem of cracks in RC columns
Problem of cracks in RC columns
(OP)
Hello,
The structure is a space frame supported on 15 RC columns (3x5). Columns height is about 12 m, their diameter is 60 cm. 5 columns, on the same axis, present vertical cracks in their mid-height in addition of a visible deflection.
A site visit will be arranged in the comming days and rebound hammer and cover meter tests will be performed. We suspect a lack of concrete resistance or cover.
Your opinions and suggestions are welcome.
Regards.







The structure is a space frame supported on 15 RC columns (3x5). Columns height is about 12 m, their diameter is 60 cm. 5 columns, on the same axis, present vertical cracks in their mid-height in addition of a visible deflection.
A site visit will be arranged in the comming days and rebound hammer and cover meter tests will be performed. We suspect a lack of concrete resistance or cover.
Your opinions and suggestions are welcome.
Regards.






RE: Problem of cracks in RC columns
Based on the condition of the space frame, I would say the environment is quite severe.
I would check for carbonation depth in the columns. Carbonation to a significant depth, leading to corrosion of the reinforcement, would be my guess.
The cover meter would be useful, but forget the rebound hammer. That won't give you any useful information.
RE: Problem of cracks in RC columns
Chip off a cracked/spalled piece of concrete, break it in two to expose a 'fresh' surface and use phenolphthalein indicator solution to check for depth of carbonation.
If the structure is in a coastal environment you may also have increased chloride content, and it is easy to take samples and get them lab tested.
If it gets more 'complicated' you could take cores samples and do petrographic analysis/testing.
RE: Problem of cracks in RC columns
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RE: Problem of cracks in RC columns
Indeed, the structure is in a coastal environment is Saudi Arabia.
We thinked about coring samples and performing resistance, carbonation and chloride and sulphate content tests , but we were afraid this could cause damage to the columns since the cores are 100mm in diameter and up to 300mm long for only 600mm of diameter fo the column.
The problem is that the cracks are located only in the mid-length, between construction joints, for only 5 aligned columns, we think the quality of the concrete mix for these parts is pour. Is there any possibilities of repairs if carbonation or chloride content is proven ?
Thank you.
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
The space frame also looks to be in bad shape. I see peeling paint in your pictures and I suspect it is corroded. Maybe it's time to price a new structure and replace.
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
Really spindally, what type of bracing? Looks to be too recent for carbonation to be an issue. Doesn't look like a rebar problem, but, if near coastal areas, you should have a couple of inches of cover and maybe HDG rebar.
Dik
RE: Problem of cracks in RC columns
Why do you need such large dia core samples?
2" dia cores for a 4" depth will usually be satisfactory for Cl- testing and petrographic analysis. 2" cores can be sometime used for compression strength testing too after you factor in H/D ratio and use adequate test capping.
RE: Problem of cracks in RC columns
None of this leads to 'why the cracks formed'; the procedure for construction has to be reviewed.
Dik
RE: Problem of cracks in RC columns
Dik
RE: Problem of cracks in RC columns
The structure was constructed in the 1980's, unfortunately, we don't have any information about its construction procedure.
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
Dik
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
One in the hand is worth two in the bush.
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
Propose to take cores of both defective areas on "bad" columns and similar locations on "good" columns. Test results will likely show no significant difference in the concrete. Explain that failure of some columns (to this date), but not others, is probably caused by either minor variations in concrete or just luck. As a former Owner, this is the type hard evidence that makes a convincing presentation.
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RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
At least in the US I'd get a friendly contractor to weigh in (someone looking to be helpful, not just looking to make more work for themselves). And make sure they know the space frame is getting replaced too so they know they don't have to shore it up before removing the columns, also that there's no foundation work (assuming there actually isn't). Here in the US it would almost certainly be faster and very likely cheaper to just take the columns down and build new than to figure out what's wrong, design for what's wrong, and then build the fix. It's also possible you go through that whole process and the 'fix' is you still have to tear them down and rebuild.
I have never known an owner to insist on fixing an old structure for more money and more time when they have the option to tear it down and build a new one for less money and less time.
RE: Problem of cracks in RC columns
I've come back to you again.
I've just finished investigation of the concrete columns. I'm waiting for laboratory results.
I've opened some cracks and noticed that concrete is fragile to a certain depth, until the rebars for some cracks, and the steel is corroded by different degrees. In one column,I've noticed a relatively advanced level of corrosion in one rebar, in the cracked zone,
and no corrosion in the next rebar, just below the cracked zone.
Similar cracks, but less wide, are noticed in some other columns in the two other axes. I've opened one of them and heve seen a relatively advanced level of corrosion with a relatively small cover comparing to others.
In the same column, at the same level, the concrete seems to be different from the north surfaces and the south ones, there is a difference in colour, look and sounds to hammer, escpecially the cracked ones, they sound very hollow from one side. It's almost the same for the 15 columns.
The problems seem to be due to carbonation or chloride attack on the concrete, accelerated by bad mix of concrete in these portions of these 5 columns and a lack of cover may be in another column.
We have taken 3 cores, 3 upv tests, some drill samples and some rebound hammer tests. We are waiting for compressive strength on the cores and chemical analysis.
What do you think ?
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
If it was up to me, I would replace them, it would be too much easier and safer, but it's more complicated, the contract scope is about replacing the roof and repairing the columns.
The final tests will be more determinant.
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
RE: Problem of cracks in RC columns
Again,