Retro-fitting of rusted reinfocement ( beam and col ) 5

[ksdphilippines]

Good day to all!

Our company ( a construction firm ) has been approached to check on a rusted reinforcements of slab, beam and rebars under the Comfort rooms of a school building.

The building is quite old ( around 30 years ). The beams and slab has already cracked mainly due to the expansion of reinforcements.

The problem may have started with the waterproofing of the CRs which were not done correctly or not placed at all.

Anyway, the second floor column has also rusted reinforcements which has been exposed already. The building is 6 storeys high.

Queries :

1.) What measures can be done for this problem?
( confined only to the CR area )

2.) We were looking into planting a new system of columns beams and slab for the area from ground floor. Are there other options?


your response will be greatly appreciated...

Bet regards.

 

[Ron]

The first step is to assess the amount of section loss you have in the reinforcement and quickly determine the safety of the structure!! Get both structural and materials engineers involved in this decision. Once that has been done there are several methods of remediation from direct replacement to carbon fiber wrapping the members.

A complete study should be undertaken and quickly as you have damaged building components under stress.

30 years is not "quite old". A properly designed, constructed and maintained reinforced concrete structure should perform many years past "30".

 

[LPPE]

I was going to suggest what Ron suggested - carbon fiber wrapping may be an option. First things first - stop the water infiltration. Also, like Ron said, a properly designed and maintained structure should last AT LEAST 30 years.

 

[dicksewerrat]

After you get the building safe enough to work in, get a plumber in to redo the piping. There are either leaks in the supply lines or waste lines. This damage may bemuch for 'sweating' supply lines.

 

[dbuzz]

Recommend installation of carbon fibre reinforced polymer strips to the underside of the concrete slab, such as Sika Carbodur (

http://www.sika.com/cmc/constr-business-01/struct-strength-01.htm),

and repair of slab to prevent future moisture ingress.

 

[ksdphilippines]

Thanks for all the replies you've given... All are very much helpful...

Anyway, just curious if there is a protective coating product for reinforcing bars. A protective covering that need not be stripped off the bars prior to concreting...

If so, any websites I can go to?

More power.

 

[dbuzz]

Two options are epoxy coating and galvanising. A galvanised coating is usually 80 to 100 microns thick, however is susceptible to damage during handling and placement. Also, the galvanised layer can react with the cement in the concrete to produce hydrogen, which may cause embrittlement of the steel. Consequently, the bars should be passivated in a sodium dichromate solution.

Also, alternative materials such as stainless steel are suitable for extremely aggressive conditions.

 

[Focht3]

Hmmm,

While all of the suggestions you have received are good, you also need to look at whether calcium chloride (CaCl) was added to the concrete to accelerate curing, or the concrete contains some other agent that is promoting rebar corrosion. This could be a significant factor in the expansion of the rebar.

Are you replacing the columns entirely, or just "rehabilitating" them? If the concrete itself is a problem, I'm not sure that simply coating the rebar will solve the problem permanently.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[ksdphilippines]

focht3,

We are evaluating which options to choose... either rehabilitate or replace....

thanks for all your answers.

If there are still other opinions... kindly post...

 

[Focht3]

Do you really know why the rebar is rusting?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[ksdphilippines]

We are designing a retaining wall near a proposed four-storey building. The retaining wall will be located on the riverside.

Our concern will be on how much surcharge to use (caused by the building)?

Any leads on how to compute surcharges in general?

 

[SperlingPE]

ACI offers a report from ACI 201 committee that deals with evaluating concrete structures.
Safety should be the first concern. Secondly, the cause of the corrosion should be stopped. Finally, repair of the structure.