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]

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?

 

[hokie66]

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.

 

[khinz]

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/honeycombhammerclear.jpg

 

[Ron]

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.

 

[khinz]

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.

 

[hokie66]

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.

 

[khinz]

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?

 

[hokie66]

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.

 

[khinz]

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.

 

[hokie66]

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.

 

[khinz]

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?

 

[PUEngineer]

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

 

[khinz]

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/honeycombwhite.jpg

 

[Ron]

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.

 

[khinz]

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?

 

[a7x1984]

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!

 

[dik]

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

 

[khinz]

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?

 

[khinz]

by the way, here's the link to the description above for those who can't view it direct
here

http://imageshack.us/photo/my-images/844/honeycombfix.jpg/

 

[Ron]

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.