Horizontal Column Cracks During Curing 7

[YuleMsee]

What went wrong here, column ain't loaded yet, just cured. Its A 600mm DIA. column, 8D20 bars, D8 links @ 225mm spacing concrete class 25.

 

[jayrod12]

Those certainly appear to be at each link location. Perhaps too soupy of a mix, shrinkage cracking at the thinnest areas. Are we sure about how much cover was provided? How runny of mix? Based on the formwork props I'd venture to say that concrete admixtures are rare in that area, therefore if the mix was runny, that may indicate a high W/cm ratio and tehrefore increased shrinkage cracking.

 

[YuleMsee]

Cover in drawings is 30mm, problem is after inspecting reinforcement sizes and link spacing nobody is there to ensure correct placement of formwork nor check slump while concreting.

 

[jayrod12]

You could have them chip away the concrete to check cover depth.

If the concrete had water added, which would be a concern, it would show up of the compressive testing.

 

[Blackstar123]

Are the cracks all around the column or just at this particular face? Also how many columns are cracked like this?

Euphoria is when you learn something new.

 

[r13]

Maybe caused by optical illusion, I feel the column behind this one has tilted toward the left. I highly suspect the cracks are drying shrinkage caused by high W/C ratio, or excessive addition of water during concrete placement. Take samples for compressive test if concrete lab is available.

 

[YuleMsee]

Blackstar, its on two faces, and 4 columns in a total of 40, although not all were cast the same day

 

[oldestguy]

Were these columns filled one at a time with hand mixed batches such as one wheel barrow at a a time? And very wet? Or just placed one wheel barrow load at a time?

 

[Tomfh]

Looks like the cage was leaning against the formwork.

 

[BUGGAR]

Look like cold joints???? Lack of vibration.

 

[JLNJ]

Looks like the piers were placed one 5 gallon bucket at a time.

 

[hokie66]

Those are not drying shrinkage cracks. They formed while the concrete was plastic. They are called plastic settlement cracks, because the still plastic concrete is supported by the ties , but settles below. The root cause for the cracks is inadequate consolidation. Was the concrete in these columns vibrated at all?

 

[Blackstar123]

hokie66 assessment seems logical.

Euphoria is when you learn something new.

 

[Ron]

hokie66 is correct. Particularly evident in high slump mixes.

 

[YuleMsee]

@oldestguy @JLNJ, yes they were done with wheel barrows, what is the connection between how concrete is transported and the cracks?

@hokie66, yes, vibration was definitely done, no honey combing has been observed but no way to tell if it was done adequately.Your explanation makes alot of sense

 

[kipfoot]

ACI has a webinar presentation on this topic: Dealing with Plastic Settlement Cracking: Case Studies and Lessons Learned

This is new to me, so I'm grateful for the discussion. The case studies in this video are mainly flatwork, but it seems like a good overview.

 

[r13]

Good point. I recall ACI318 used to have a requirement, that for deep members, a horizontal bar should be placed directly under the top reinforcement within a certain distance to avoid occurrence of air pockets below the main reinforcement due to "plastic settlement". I don't know if this provision is still there or not.

 

[r13]

IMO, I still think excessive high W/C ratio was the main culprit, also due to rapid concreting, the water was locked in that couldn't escape. When drying stared to occur, the middle core settled more, and more rapid, as opposed to the cover that was confined by the reinforcing and the form. A drag force thus created that causing the separation.

 

[RPMG]

retired, you're describing plastic settlement cracks, except the self weight of the concrete should close those gaps. There would probably have to be unconsolidated concrete and other factors such as a high W/C ratio.

 

[r13]

RPMG,

Yes, it occurred in a stage considered the concrete is plastic like. But for very high W/C ratio, I feel the mix is more soup like than plastic. The voids occurred after losing water need to be filled by concrete above, thus the drag is larger than normal.