concrete beam repair 5

[BigInch]

Hi,

I've got a problem with a small concrete beam, roughly 400mm x 200 mm wide, forming part of the roof support of an underground pump house. The top of the beam is flush with grade elevation. The span is not more than 2.5 meters, with very little real load from the adjacent 1 m wide slab that can only accept foot traffic. There has been considerable water penetration from the adjacent earth and surface dripping and the bottom of the beam has deteriorated with the humidity to the point where the outer clear distance has spalled off and the bars have become exposed and rusted. It has two temporary supports holding the beam up now, but I think that those might not really be necessary; just a safety measaure. I'm not sure, so I will verify the full extent of damage. My question is, provided the exposed bars are still sound, is there a way to replace the concrete lost from the beam, perhaps using epoxy grout formed to replace the original concrete clear cover around the existing bars, or is there some other method I could be looking at? I would imagine that all depends on the present integrity of those rusted tension bars. If necessary, is it possible to replace the bars themselves and if so, how would one go about doing that?

Any advice on the matter is greatly appreciated.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO, BP
**********************
"Being [c

 

[dgkhan]

You can brush clean the rusted rebars and place new adjacent up to lap lentgh. YOu can apply epxy grout to bring back full section of beam. Make sure to wire brush to expose aggregates to 1/4" amplitude.
Alternatively there are many fibre reinforced polymer sheets/ compounds available. One is Aquawrap. you can read there manul to see how to use.
I tend to stay conventional unless the HIGH cost associated with new product is justified.

 

[Ron]

Expose the rebar with about 20mm clearance all around. Wire brush the rebar to remove all loose rust and debris. Do the same with the exposed concrete face. Form slightly larger than original beam and pour polymer concrete repair mortar in form to fill bottom of beam and up sides at least 1/2 way.

I would use SikaTop 111 Plus, extended with coarse sand or Sika MonoTop 611, also extended with coarse sand. Both can be flowable and will achieve more than 35MPa

 

[DaveAtkins]

I agree with Ron--you need to expose the rebar all the way around for a proper repair. Since this seems to be an aggressive environment, you might want to coat the rebars with spray-on or brush-on epoxy prior to completing the repair as Ron described.

DaveAtkins

 

[BigInch]

I had a little better view today and there doesn't appear to be any interior cracking of the beam; just the spalling off the bottom. I suspect the clarence was inadequate to begin with. The salt water wasn't helping.

Thanks very much Dave and Ron. I understand clearly what we should be looking to do. Thanks Ron especially for the brand and material designation. I'll have to see if that's available in Spain, or hunt up an equal product.

Another happy customer!

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.co

 

[Ron]

BigInch...here's a link to their website for Spain...

http://www.sika.es/

 

[BigInch]

Excellente!

I'll bet that makes one hellova paella.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.co

 

[Ron]

OK..it's lunchtime here...now I'm hungry

 

[BigInch]

I'll share,

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.co

 

[nuche1973]

I just finished a project similar to this: Humid environment, rusting reinforcing. The culprit was carbonation of the concrete leading to corrosion of the reinforcing. This was determined after petrographic analysis. We also recommended implementing galvanic anodes along with coating the rebar and sealing the final concrete surface.

 

[JedClampett]

I've seen this before and surmised that the cause was the reinforcing chairs. The legs are exposed to the nasty atmosphere and they communicate the galvanic action to the main bars.
By the time I got to it, the beam steel was gone and I had to resupport the slab. A couple of years later the problem had continued unseen into the slab and that was that.

 

[SkiisAndBikes]

I would like to add to the above suggestions. Ensure that all deteriorated concrete is removed to a minimum depth of 1 inch above the reinforcing bars. Ensure the jackhammers do not leave behind any bruised concrete. Sawcut the perimeter of the repair area 1/4" deep to provide a proper termination and prevent feather edging. I strongly recommend sandblasting (or alternately medium pressure water blasting) the rebar and bonding concrete surface. Application of a bonding agent and protective coating to the rebar can be tricky if you cannot get the forms installed and the repair material placed before the contact time is over. A product similar to Sika Armtec 110 is a cementitious epoxy bonding agent with a comparitively long contact time. Once the forms are installed, pour, pump or otherwise place a repair material compatible with the original concrete.

 

[BigInch]

Thanks for the additional info. Now I have another question about the bars themselves.

Can the bar be cut back if needed and new bars be field welded in somehow to good portions of the old bars (how do you weld bars together), or should the concrete be cut back enough to expose a proper development length and simply lapped together over that length?

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[BigInch]

And I did like the look of that carbon fiber reinforcing material on that same website. Might that be a good thing to try?

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[SkiisAndBikes]

BigInch,

It is considered good practice to continue the concrete removal, even if this involves the removal of sound concrete, along the bars until they are essentially free of significant corrosion. Some judgement required here.

For a beam length of 2.5m, it would not take long to remove the bottom section of the beam for it's full length. I would leave any existing bars in place as long as they were properly sand or hydro blasted, even if they had experienced loss of section. Lapping new bars is preferable if you have the required development length and enough space (for slabs this is easy, sometimes beams are too congested).

If you are going to try and weld new bars, you need to determine whether the existing rebar is a weldable grade.

 

[BigInch]

Got it.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[Ron]

BigInch...yes you can weld the rebar. In the US, that would be done by American Welding Society (AWS)standards. Not sure what your code would be.

As for the carbon fiber overlay...It works well, but you would need to do a lot of what you're doing already, so not sure its worth the cost in your case.

The SikaTop 111+ has a corrosion inhibitor in it, so no real need to do anything else....just clean the rebar well and make sure you get new material to flow all around it.

Carbonation is probably not the cause of deterioration here. You can check the depth of carbonation by breaking off a piece of the concrete and brushing phenolphthalien on the freshly broken piece. The non-carbonated areas will turn pink/purple. The carbonation will not change color, thus you can see the depth of carbonation. It is usually limited to about 3 to 6mm. There is a RILEM standard for the test.

 

[lsmfse]

This document also has reccomendations.
"Technical Guidelines No. 310.1R-2008, Guide for Surface Preparation for the Repair of Deteriorated Concrete resulting from Reinforcing Steel Corrosion"
It is published by the International Concrete Repair Institute.

 

[csd72]

I would recommend for a more thorough job that you do some testing on what distance the salt has penetrated.

You may find that after this is repaired a new area will start corroding in only a couple of years. Best to find out the root cause and address it in one go.

There are other rehab products that are available from the same companies such as sacrificial anodes that attach to the rebar or coating to protect the concrete surface against further contaminants.

Once you have the full details then you can get the rep from Sika to recommend an optimum and a minimum treatment.

I would recommend against cutting the rebar, just weld a new bar either side.

 

[BigInch]

OK. Yes some proofing of the outside surfaces and adding some slope to drain any water away faster could both be appropriate.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv