Column discoloration 5

[khinz]

What is this discoloration in the lower part of the column? it's not honeycomb because I tried hammering it and there is no honeycomb. Anyone has encountered this? How do you fix it?

 

[khinz]

Ron, are you saying it is still soft inside? but we tried hammering and it looks hard. Is it not you fix honeycomb by removing the soft part. The concrete supplier explained that when the concrete is poured from the concrete truck, it hits one side so the aggregates go to the outside part and the vibrator missed the outside part.

About this "potentially insufficient paste in areas of accumulated coarse aggregate".. is this not what honeycomb is all about? or is it worse than honeycomb? how? by the way, it's just the lower 1 meter of the 3 meter high column.

 

[khinz]

by the way, here's the picture of the entire column, the upper part is ok.. only the 1/3 lower part is the problem, so it couldn't be bad concrete mix from the concrete truck.. maybe just the fact the lower part is not vibrated properly? what do you think?

http://imageshack.us/f/442/honeycombentirecolumn.jpg/

 

[PUEngineer]

Maybe the picture exagerates the amount of concrete removed, but where are the longitudinal bars and ties?

 

[khinz]

The stirrups are about 2mm behind where the soft honeycomb is removed. Can anyone give a theory whether it is leaky formwork or the outer part not vibrated that cause the problem? But the 2/3 upper part of the column is good.

Discussing it with the foreman in case the lower portion of the concrete have to be removed. We don't have the technology to pump it from below. So the best we can do is remove the 1 meter portion of it.. put formworks and put concrete via the upper part by extending the formwork outwards and overfilling with concrete. Has anyone amongst you actually tried replacing a portion (say whole 1 meter part) of a portion of a column? We haven't tried it so if the honeycomb removed is sufficient. We don't wanna try something we haven't done before.

 

[msquared48]

PU:

That wa s my thought too... Longitudinal corner bars, let alone the ties, should be visible with that amount of concrete removed. This looks very suspect.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[khinz]

PU and MSsquared, during steel placement by the steel men, the concrete cover at the front is bigger than the back.. but then analyzing it, note it is a side column so bending moment is towards the center of the building, hence it is allowed to concentrate the bars to the other side in tension, the front is in compression as the column bending moments are toward the beams in the center of the building. I only noticed this when I saw the bars in the floor above it and didn't let them demolish the entire column because it may not be that bad.

 

[Ron]

khinz...you cannot adequately determine the integrity of concrete by how much "honeycomb" you can remove with a hammer. What several of us have been diligently trying to tell you is that when you have such poor placement of concrete, there are likely other quality problems as well, including the concrete mix.

In your photo, you appear to have elongated coarse aggregate particles with preferential, stratified alignment. Further, these stratifications appear to have little paste between them, indicating accumulated, segregated aggregate. This is different than "honeycomb" which is evidenced by sparse coarse aggregate and little paste.

The concrete supplier explained that when the concrete is poured from the concrete truck, it hits one side so the aggregates go to the outside part and the vibrator missed the outside part.

You stated that the concrete was pumped. The concrete in the column has little to do with how it came out of the truck, since it was pumped from there. It is likely the segregation occurred from dropping the concrete a long distance, as you can see that consolidation was better as you when up the column. Further, you stated that vibration was done from the top. This would not allow full vibration of the concrete to the bottom of the column. Each of these is a bad practice in itself.

If you review the ready mix delivery tickets, you might find that the concrete was relatively old when placed and was losing slump. Further, there's a chance that the aggregates were not in a saturated surface dry (SSD) condition with the concrete was batched, thus caused water loss by aggregate absorption.

You further indicated that the drum of the truck was rotating when delivered....well of course it was. It should have been. Your comments suggest that you know little about concrete technology and yet you are being placed in a position of accepting conditions about which you know little and have not determined some critical aspects of the concrete as it exists in place, particularly interior to the column (strength, voids, segregation, etc.). I suggest that if you have any authority whatsoever that matches the responsibility you seem to have been give, you should exercise it and get the bad concrete out of the column.

Concrete is not nearly as simple as it appears. It takes concerted effort by multiple parties to get concrete design, batching, mixing, placement and curing done correctly. Much of the time that seems to happen without such effort; however, that is with experienced actions all around.

Good luck.

 

[khinz]

Ron, you wrote : "In your photo, you appear to have elongated coarse aggregate particles with preferential, stratified alignment. Further, these stratifications appear to have little paste between them, indicating accumulated, segregated aggregate. This is different than "honeycomb" which is evidenced by sparse coarse aggregate and little paste."

so there are placement that is different from honeycomb. The following pic is in opposite side of the column we are talking about. Is the column bad portion a result of
this descriptions "elongated coarse aggregate particles with preferential, stratified alignment. Further, these stratifications appear to have little paste between them, indicating accumulated, segregated aggregate"?? I've been looking for ways to describe it. Did the above describe it accurately? if not, pls. add more so we know what went wrong and can decide how bad it is.

http://imageshack.us/f/822/columnback.jpg/

we are just small company and don't have much crews and engineers.

 

[dik]

How heavily loaded is the column? I suspect with 2.5% you may have a cluster of perimeter bars with 'cross-ties'... and also with 2.5% it could be somewhat heavily loaded...

Problem is not going away... time to quit dikkin'

 

[Ron]

kninz...I agree with dik....move on.

Anything else we can provide from photographs is purely speculation. You need to decide if you want to do further testing or just take it out and re-do the column. I think if you do testing it will lead to the same decision as you should be making now....tear out the bad concrete.

Being a small company has nothing to do with it. If your company was large enough to do the job, they are large enough to fix their mistakes. You are simply prolonging the inevitable.

 

[hokie66]

You have been given excellent advice, especially by Ron. This column should be rejected, and there is not much more we can do about it.

 

[khinz]

Dik, Ron and hokie, etc. the following picture is what the rebars look like inside (I photographed it before the column was casted with concrete). The lower portion has stirrups spaced 80mm apart and 3 sets of stirrups with 4 bars at each side of the column (total of 16 bars). Let's say we remove the concrete at the lower one meter. How are we going to put concrete and insert vibrator when the stirrups are 80mm apart in the lower part and we can't pump it up from below but have to do forms with concrete put from the top. Btw.. the building is 3-storey with metal roof, the column is in the second floor so it has one floor to support above and a metal roof above it. The column is somewhat overdesigned for safety factor.

http://img824.imageshack.us/img824/8219/columnrebars.jpg

 

[khinz]

The building main and only seismic system is concrete special moment frame so I may try to remove the concrete for peace of mind. Based on the above picture of the rebars inside and the stirrups being mere 80mm apart in the lower bottom. Can we just use chipping gun? But how can it even be inserted inside the 80mm spaced stirrups? And for a 1 meter concrete replacement, can it do without vibration at the bottom since we can't insert any vibrator thru the closely spaced stirrups?