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Column discoloration
5

Column discoloration

Column discoloration

(OP)

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?

RE: Column discoloration

Was fly ash used in the mix? If so, there may not be any way to fix the discoloration.

RE: Column discoloration

(OP)

What's fly ash? why is it in the lower part of the column? I'm thinking whether it may be cause by some water leaking out leaving the cement behind (that's why it has color of cement, is this possible)? It's not honeycomb. No one has encountered this yet?

RE: Column discoloration

What is the colour range? Can you post a photo that shows it?

Dik

RE: Column discoloration

Fly ash is an admixture used to reduce the amount of cement needed. It is a byproduct of the coal power generating process and can reduce the cost of concrete significantly without reducing the strength significantly when portioned correctly. However, fly ash can cause streaking and discoloration of the concrete.

RE: Column discoloration

(OP)
this is another column nearby with honeycomb.. note the same color pattern




the original picture has no honeycomb but has same color pattern as the honeycomb.. could it be lack of water in the concrete or in the verge of honeycomb?

About the picture above... hammering it appear it is only in the concrete cover.. is it serious enough to warrant removing the entire layer of the concrete and pouring new one? What have you experienced?

RE: Column discoloration

When looking at the first picture I thought maybe it had some patching at the base, but the second picture doesn't agree with that thought.

Are you worried about structural issues? I wouldn't worry about structural issues, however I'd suggest that any loose material be removed and then the honeycombing should be patched; if it's truely just in the cover as you've stated. If you're still worried about structural issues, not exactly conclusive, but you could have the surface tested with a swiss hammer or something of the like.

RE: Column discoloration

(OP)


How do you tell how deep it extends? I see solid concrete inside but not sure if there is micro honeycombs.. I don't want to keep hammering it because it can reach further inside.

When you use hammer on concrete.. is it supposed to be damaged significantly? how do I know if the hammer is removing honeycomb or normal concrete?

RE: Column discoloration

Depends on the hammer; sounding hammer, framing hammer, sledge hammer, jack hammer, hammer scampi, etc. In my experience with a normal framing hammer; a good solid 'drive a nail in one swing' type of 'whack' shouldn't do much damage. That depends a little on how green the concrete is, it might dent the surface a little.

RE: Column discoloration

(OP)

how long in your experience does the concrete stay green before it gets super hard? during green, it can be strike with hammer? i use a normal carpenter nail hammer

RE: Column discoloration

(OP)

by the way.. in honeycombing pictures in the net, they honeycomb is same color as concrete (whitish).. but in the columns I saw, the honeycombs have color of fresh cement grout, the first picture has the same color but no honeycomb.. any theory where the colors come from especially in the first page picture?

RE: Column discoloration

There have been questions about the use of fly ash, you haven't responded to that. What does the contractor or concrete supplier say about your concern? Was the slump high enough to cause segregation? What were the vibration techniques used?

RE: Column discoloration

My guess for the discolouration would be that an excessive amount of form release oil was used. As to the honeycombing, leaky forms and/or inadequate consolidation.

RE: Column discoloration

(OP)

The slump is 3/4 aggregates and it's 4000 psi concrete with only $2 difference to 3000 psi so admixture is probably used. The concrete supplier won't say what they use since it's company secret and they said they only supply concrete. But let's say it's ash fly, why is it at the bottom only? The contractor doesn't know either although the foreman said before concrete is pour, a liquid basin of grout cement is poured inside to seal any cement cracks in the surface of the previous lift at the floor level, could the discoloration at the bottom be from this liquid basin of grout cement? Vibrator technique is adequate as the hose is lowered all the way to the bottom and every sides and center vibrated.

Here's another picture of it at another angle. Is there no possibility it is caused by water leaking out of the cement rather than the honeycomb principle of cement leaking out of the aggregate?

RE: Column discoloration

"Liquid basin of grout cement"? That could be your answer, and could present a bigger problem than discolouration. Why are you concerned about discolouration? This certainly does not appear to be architecturally exposed concrete.

RE: Column discoloration

(OP)

but if you will note about the second picture (or again the following), the discoloration is half the height of the column in the location of the honeycombs. So it could be related to some liquid leaking. So i guess micro liquid leaking just cause the discoloration at bottom without honeycomb. More liquid leaking gives full fledge honeycomb. What do you think of this theory?

RE: Column discoloration

One of two reasons for discoloration...excessive form release or mortar "pig" from pump. Not likely fly ash as it would not segregate in that manner...too fine.

RE: Column discoloration

(OP)

mortal "pig" from pump? what's that? no, the pump crete hose wasn't directly aimed inside the formwork but the column was filled up by aiming at a board on top of the column opening.


for the separate issue of honeycombing. Has anyone ever used epoxy in treating honeycomb? a worker suggested the honeycomb need not be removed but epoxy can be pumped thru the holes at high pressure filling up all spaces inside the honeycomb. has anyone ever used this technique? or is this never used?

RE: Column discoloration

The mortar pig, as Ron called it, is the same no matter how it was placed, but the way you described will invariably lead to segregation.

Don't listen to that worker. You can't be sure of filling all honeycombing voids by injecting epoxy.

RE: Column discoloration

(OP)

this is close up of the discoloration in the vicinity of the honeycomb (the left I hammer to see how deep it is, it's not deep enough is it).. haven't any of you guys ever encountered it before? it's only in the vicinity of the honeycomb so it must be related to leak or segregation problem. any other theories?

RE: Column discoloration

(OP)

this is close up of the discoloration and honeycomb, i hammer the left side to see how deep it is, it doesn't look deep enough, is it. The discoloration must be related to the honeycomb because it only appears in the vicinity of the honeycomb (left and right side). Any other theory beside fly ask, mortal pig, etc.? note it only appears in the vicinity of the honeycomb. haven't anyone amongst you encountered this before?

RE: Column discoloration

That picture didn't come through. By the way, the mortar in the pump was probably discharged into the column just to get rid of it, not for any beneficial purpose. The reason for the mortar is to lubricate the pump line, and should be discarded.

RE: Column discoloration

(OP)
here is the direct link of the detailed close up of the honeycombs and discoloration (based from it, the honeycomb on left is not deep enough? note the discoloration in the vicinity of the honeycombs.. could the discoloration be related to leaked or segregation problem):


http://img441.imageshack.us/img441/3513/honeycombh...

RE: Column discoloration

khinz...you have some significant placement problems. The honeycomb, the discoloration, some apparent efflorescence...all indicative of mix and placement issues. Based on the size of your columns and the amount and location of the lack of consolidation (honeycomb), I would reject the placement.

RE: Column discoloration

(OP)

do you suggest demolishing the column and recasting it? but it is 4000 psi, can the concrete be safely demolished without damaging the more fragile grade 60 bars?

btw.. it's not a mortal "pig" problem because I remember that when the pump hose were connected and before concrete was put in the columns, the initial mortal was thrown away so it couldn't be mortal pig.

RE: Column discoloration

Agree with Ron. I would reject that column. There are several ways it can be removed, but you can remove the concrete without damaging the bars. The sooner the better, as it is not 4000 psi yet.

RE: Column discoloration

(OP)
but the part with the problem is only the lower one third of the column.. maybe only the lower portion should be demolished and recasted in that portion or does the entire column including the good 2/3 upper have to be demolished and casted as well? What is usually done?

RE: Column discoloration

Assuming there is nothing cast above the column yet, what would be the advantage of saving the top part? Much simpler and more economical to cast a whole column than just the bottom part.

RE: Column discoloration

(OP)

unfortunately there are already beams and slabs in next floor cast above the column. So only the lower one third column needs to be replaced. But if you will insert new concrete, concrete can settle.. how do they handle this? is this even possible at all? What have others actually use in solving this? The supports of the upper beams and slabs are still in place.. we just didn't notice the honeycombs because the formworks were taken out too late.

RE: Column discoloration

Yes, you can break out the defective concrete and cast it again. One way is to build adequate formwork so that the concrete can be pumped up from the bottom through a hole in the formwork. Would require steel forms, I think. Another way is to cast it to within say 50 mm of the joint, then grout that section with non-shrink grout.

It is always best to inspect lower elements first before casting something above...but I'm sure you know that now.

RE: Column discoloration

(OP)
Ron or others, how can efflorescence form in newly cast concrete in the column? any chemical details? If you see it in your new column, would you automatically reject it, and is it worse than honeycomb?

RE: Column discoloration

Why are there bars sticking out of the column? And what's the blue stuff in the area of honeycomb that you removed?

RE: Column discoloration

(OP)

the bar is a dowel to connect the the column to the wall at the side.. the blue i don't know...

anyway.. i found out the reason for the discoloration, it's because water was used 20 minutes before I photographed it and they stayed in the honeycomb section longer that's why the honeycomb section appeared darker. In the following picture is the same column but with no water sprayed for an hour. So it may not be as bad as the earlier picture. Although hammering indicates it is not honeycomb passed the concrete cover section. I'm worried it may be soft inside. Can anyone recognize if the column is salvageable without replacing an entire section... what equipments like x-ray can be used to inspect inside.. has anyone used one

http://img692.imageshack.us/img692/5261/honeycombw...

RE: Column discoloration

Radiography of a section this large will be expensive, time consuming, and will not likely yield anything you don't already know...you have voids. It will show the "far side" rebar, but you likely know where that is as well.

Low frequency ultrasonics or other similar scanning techniques would be less expensive and can be used to locate larger interior voids. Will be good substantiation if you reject the column.

Efflorescence is simply and indication of excessive moisture moving in and out of the concrete. It can indicate that your concrete is more permeable than desired. It has little effect on the concrete or the performance of the column structurally, but can more quickly allow carbonation of the concrete to greater depths, thus increasing the potential for rebar corrosion if exposed.

RE: Column discoloration

(OP)

after removing all the honeycomb soft concrete and creating a key like shape, can one just fill it with epoxy instead of concrete? what is the psi of epoxy.. maybe this would be better for shallower honeycomb as it would adhere better to existing concrete since it is epoxy?

RE: Column discoloration

Shallow repair depths usually require a specialized repair mortar - Epoxy alone is not used for patching. Here is a list of ones with varying additives: Sika Repair Mortars

In Russia building design you!

RE: Column discoloration

Sorry for the comment about photos... appears that our IT department's filters are at work...

The concrete does not appear to be discoloured by excessive form oil, but appears to be suffering from poor concrete placement. What is the height of the column and what percentage of reinforcing. What sort of placing procedure did you use for the concrete and what mechanical vibration? The discolouration appears to be from segregation.

Rather than spend time examining the condition of the poor concrete, it's better to remove it ASAP. This can be done with hydroblasting or carefully use some mechanical means as not to damage the reinforcing steel.

Dik

RE: Column discoloration

(OP)

The column size is 400x500mm... reinforcement percentage is 2.51%, the concrete came from a concrete truck that is rotating, placement is via pump crete and then the concrete down in a 3 meter tall column with vibrators inside. The following is the picture after we remove all the soft honeycomb, only the outer part is soft so I think the column is salvegeable since no bars exposed, all the concrete are already hard inside. Maybe the vibrator was not used on the outside. You agree it is salveable? Now my next step is what mortal to use to patch it. Do you think normal concrete in 1-2-3 combo will be sufficient?



RE: Column discoloration

No. I would not agree it can be salvaged without removal of the concrete. It appears that you have segregation and potentially insufficient paste in areas of accumulated coarse aggregate. This is a problem.

Just because the concrete seems "hard" on the inside does not by any means indicate you don't have a problem with it. Assuming that can get you into a lot of trouble.

Stop playing with it and get on with the remediation. As dik recommends, hydroblasting would work.

RE: Column discoloration

(OP)

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.

RE: Column discoloration

(OP)

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.j...

RE: Column discoloration

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

RE: Column discoloration

(OP)

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.

RE: Column discoloration

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

RE: Column discoloration

(OP)
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.

RE: Column discoloration

2
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.

Quote (khinz)

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.

RE: Column discoloration

(OP)

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.

RE: Column discoloration

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'

RE: Column discoloration

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.

RE: Column discoloration

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.

RE: Column discoloration

(OP)

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/columnreba...

RE: Column discoloration

(OP)

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?

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