Repair of Slab Soffits 1

[Meesamali512]

Hi Everybody,

We have a project of repair of concrete frame structure. We have to repair the slab soffits, slab's upper portion, beams as well as columns. For columns, beams and upper portion of slab we have standardized methodologies and techniques. The problem arises for the repair of slab soffit using ordinary M40 concrete.

It is understood that many kinds of cementitious repair mortars can be used for slab soffit repair as a patch repair but we have to use only "Ordinary OPC M40" concrete as this is the requirement of client. Also its cost is far lesser than cementitious repair mortars.

One of the suggestion is to use a pump from the bottom to push the concrete to formwork but this doesn't sound practical enough and aggregate size will greatly affect the pumpability from below. Another option is to drill a core through slab from top but that is also not allowed by client as it will compromise the integrity of structure.

Would appreciate any suitable, reasonable as well as practicable solution from anybody.

Regards

 

[dik]

Check with Sika and see what type of cementitious patch they can recommend... Matter of hydroblasting or something of that ilk to clean the existing concrete surface. Why is the soffit damaged? Rebar corrosion? You may require more than a patch...

Dik

 

[Meesamali512]

Actually we had a meeting in our office with Conmix (another supplier like Sika). He said there is no way except patch repair using patching mortars. Soffit requires repairs due to concrete spalling at certain areas as well as rebar corrosion in other. Actually its a live urea plant and they have lot of chemical stuff. What client wants is a very cheap but cost-effective solution.

 

[dik]

Have you hammer tested the entire soffit? Using a chain drag is a little trickier...

Check materials and concrete cover for suitability.

Also check the concrete for depth of urea intrusion... take cores and have some lab tests done. Determine the cause of corrosion and using other testing, the extent and severity.

There may not be a very cheap solution...

I turned down a proposal to 'repair' a parkade in Winnipeg... it had been constructed several decades ago, using relatively low strength concrete and 3/4" cover to rebar... the scope of the repair would be a 'bandaid' on a far more serious injury.

Dik

 

[TXStructural]

Frequently, the patch will trap moisture and chemicals (usually salt, but any corrosive agent)against the reinforcement. The best repair strategy is usually to clear all concrete from around bars which are exposed by spalling, allowing repair materials to fully embed the bars or wire. Treat the exposed reinforcement with a corrosion preventative and bonding agent, and install a trowel-applied repair mortar. For large areas and deep repairs, forming and pumping may be economical. Be sure to use a pumpable material, and use a compatible admixture to ensure flowability (like a polycarboxylate.)

As part of the repair, assure that the top side of the slab is not collecting deleterious materials and any cracks are sealed to prevent passage of water and corrosive agents into the repaired area. The easiest solution for this is usually a membrane coating of some type, but your application may make that very difficult.