Concrete or FRP Jacket for Spalled Pier

[JoshH726]

Please see attached photo. I've been asked to evaluate options to retrofit the existing piers of an exhaust silencer at a petrochemical facility. Original design was the one 3/4" anchor centered in a 12"x12" pier 4'-3" tall on a mat foundation. Original design was (4)-#5 bars at the corners with #4 ties at 18" (design was completed in 1979).

Request is for additional concrete to build out the pier to 18" or 21" square. But the piers are about 6" from the edge of a shared mat foundation. My first thought was frp jackets around the piers, but I don't have much experience with them. So I'm looking for pros/cons of FRP vs. concrete jackets. Does ACI 440 have all the necessary/relevant info? No seismic or wind concerns and I don't have any design loads on the equipment.

Not sure who/when placed the large diameter anchor so close to the edge. From the picture I don't see the top tie either. This is all the info I have.

Thanks in advance.

 

[bridgebuster]

From the picture, it looks like you may need to rebuild the entire pedestal from the ground up.

-there's a piece of concrete on the left side vertical face about to break off
-lower right side vertical face there's an incipient spall
-top right side, horizontal surface is broken
-the ties should have been 10" apart

With concrete repairs, once you start chipping you never know where it ends. Anyway, FRP won't work. It's meant for strengthening. Therefore, the surfaces need to be repaired prior to placing FRP.

You have two options: Rebuild the existing or jacket the pedestal. If you rebuild the pedestal, you'll need shoring; add more ties, refer to ACI 318. If you go with a jacket, you need to remove the deteriorated concrete, and blast clean the surfaces. Provide ties and a few vertical bars for the new placement. I wouldn't worry about the jacket being close to the edge. The new concrete is just preserving the existing pedestal.