Grillage, under slab repair. 1

[davides]

We are in a 1920's NYC building where our floor is intact but the ceiling below is starting to spall off the wire reinforcement and there is some partial corrosion to full failure of the wire. There is no rebar, the structural slab concrete is cinder concrete (I am told approx. 700 psi) and is approximately 5" thick. Then there is a non-structural cinder concrete top slab that is about another 4" thick. On top of that is modern waterproofing with a tile floor. There is no water entering the slab at this time. The spalling damage is due to historic water damage and carbonization and has been exacerbated by time and the continued corrosion of the wire.

We have to do the repair essentially 100% from below.

We want to do a grillage type repair from below, with 2-1/2" galvanized decking supported by 4" "railroad" beams that are tied to the structural steel.

The repair is somewhat complicated by the fact that the floor structural steel is laid out with diagnol bracing in each bay.

Is there a "standard procedure" for filling concrete or grout between the decking and the existing slab above?

Thanks for any answers!

 

[Ron]

A grout mix can be pumped from below to fill the void. It would be good if you could drill some holes from the top to allow air to escape and to verify that you have the void filled. If that isn't possible, you can provide the same effect and result with "J" shaped tubes set into the existing concrete with the short side of the "J" at the level of the existing concrete and the long side of the "J" extending back through the deck. Then when you fill the void and overpressure it slightly, the air will go out the upside down "J" tubes and you can also get some grout going into the "J" tubes to verify contact.

 

[Ron]

Something else to consider is a carbon fiber overlay repair. Check with Sika Corporation.

 

[davides]

Ron, Thanks for the info on the grout mix. I assume that pumps and grout mix are fairly standard stuff for the industry. I will check with contractors. The J tubes is a great idea.

As far as carbon fiber, I heard that was a fortune.

Have you done and shotcrete repairs from below?

Thanks again