Concrete repairs in "tight" quarters

[mike80]

We are preparing rehab plans for a concrete frame viaduct. At the expansion joints in the deck, double-column piers were used to allow for the thermal movement. The clearance between the faces of the double-columns is only 8". Of course, this is also where the majority of the deterioration has occured. The column widths vary from 4 feet to 6 feet, measured perpendicular to the 8" dimension.

It seems it will be very difficult for a contractor to remove and replace the concrete on the two faces which are 8" apart. Does anyone have experience or suggestions on how these repairs can be made? I would prefer not to remove one column, repair the second, then rebuild the first column.

Thanks in advance for your assistance.

 

[CottageGuy]

Mike,

I gather that the deterioration is only on the backside of the columns (ie. not right through the 8&quot

The areas could be fully shored and the columns removed entirely (together), then replaced - but this is very similar to the solution that you don't want to use.

Could you remove the concrete from the front side, repairing say 1 foot at a time?? This would remove 25%+/- of the column (design checked of course) at a time. It would take time once you wait for curing and strength gain, but I expect you have more to repair than just these two columns.

This is a good "engineering problem". The solutions will be interesting.
Cottage Guy.

 

[Ron]

mike80...this might be a good application for carbon fiber composite strengthening. This is done using a carbon fiber cloth set in an epoxy resin.

If you can scabble the concrete down to sound material, you can build it back out with polymer modified concrete repair mortar, then wrap with carbon fiber system. This works well in tight quarters.

 

[mike80]

Ron,

I had considered the use of fiber wrap, but didn't know if the deteriorated concrete had to be removed. With the width of the piers, the removal is as difficult as the replacement of the concrete.

4'-6'
_________________________
| |
| | 2'
|_________________________|
_________________________ 8"
| |
| | 2'
|_________________________|


Perhaps the above sketch will clarify my first posting for others. The worst of the deterioration is on the two faces 8" apart. Also, please consider I have 23 of these piers to address on the viaduct.

I have considered hydro-demolition for the two inside faces. Does anyone have experience with this in tight areas?

CottageGuy - Are you suggesting removing and repairing the columns in 1'x 2' sections along the 4'-6' length? That is something I hadn't consiered, but might be possible after I check the loads on the piers.

Thanks for your input gentlemen.


Mike

 

[JAE]

Hydro demolition is a viable option to remove bad concrete...but in your case the angle of attack may be too flat. To verify this, you might try to call a demolition contractor to take a look at it.

If you find a way to remove the bad stuff....replacing with new could possibly be accomplished by setting up an 8" thick form between the two piers (one that is collapsible - scissor type) and replace the concrete with a new mix -

How tall are these piers? For a tall pier, the replaced concrete will still try to shrink a bit - causing stress on the bond between the old and new....something to consider.

 

[mike80]

JAE

The piers vary in height from 15' to 30 or 40'. I don't anticipate the concrete being bad the full height, so I don't think shrinkage will be an issue. However, it probably would be worth noting on the plans that if the taller piers have continuous patching, it should be done in stages.

Thanks.

 

[CottageGuy]

Mike,

That's what I was suggesting. The two ends could likely be repaired from the sides, then you'd have a middle section to repair that is about 2' or 2'6". You'd have to chip a fair amount of good concrete to get back through to the bad stuff though.
I don't think that this would work though if the delaminations were up the full height of the column. I was thinking that you wer elooking a delams at the base of the column.

CottageGuy

 

[bridgebuster]

Mike:

i've been involved with many bridge substructure repair projects, more on the construction side than design. A few things to keep in mind and consider:

The contractor's scope of work needs to be as well defined as possible. (I was Resident Engineer on what was supposed to be a 24 month substructure repair project; well, the contractor exceeded all the concrete repair items in little more than a month). Unfortunately with concrete repairs, no one knows the extent of the repairs until the job is done. Nevertheless, you need to perform an in-depth inspection of each column in order to establish the approximate surface area to be repaired. From there, you should advise the client that cores be taken at several locations (through the 2' side) to get a "feel" for the depth of the defects. Keep in mind that there is no correlation between the area of a defect and its depth but having an idea about the depth will help with designing the repairs. Also, discuss chloride-ion content testing with the client. I've worked with various DOT's and they all have different opinions regarding the effect of chlorides. Typically for substructures lack of air-entrainment and freeze-thaw aren't as significant as they are with bridge decks.

For the most part, bid quantities should be by volume not area. Shallow repairs, ~1" deep, can be bid by area but always specify a minimum depth for each repair type.

Regarding your problem: Fiberwrap is intended for strength. For flexure, the manufacturer's require the surface to be repaired. However, this seems like a confinement issue, so a wrap could help. You need to check with a manufacturer like Sika. Again, having an inspection report would help with that determination. The surfaces perpendicular to the 8" dimension can be chipped out and sandblasted clean but it will be a slow process, which means expensive. If the defect is located near the center of a column, the only way to remove the damaged concrete is by chipping from the outeredge and working inward. If damage at certain columns is limited to the upper portion it may be cheaper and easier to shore the superstructure and remove the affected portion of the column entirely.

Another thing to consider is rebar corrosion. I've been on some projects where the specs required that we follow the rust in addition to removing all of the deteriorated concrete. That can get pretty expensive. You should discuss this with the client. There are differing opinions on the subject.Personally, if the concrete is solid, leave the rust alone. I've read some articles that consider the rust a form of cathodic protection. One other problem with extensive chipping, i.e when you remove the concrete behind the vertical bars, is the need to provide support for long lengths of rebars.

As far as a repair material for deep repairs on the surfaces perpendicular to the 8" dimension, consider a pump mix and formwork. Hand patching will only work near the outer edges. the pump mix should use a 3/8" (maximum) aggregate.

Hope this helps. Sorry if I was too wordy.