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Removal of concrete delaminated area from bottom of post tensioned beam?

Removal of concrete delaminated area from bottom of post tensioned beam?

Removal of concrete delaminated area from bottom of post tensioned beam?

(OP)
What is the lightest weight chipping hammer that is available for removing delaminated concrete from the bottom of a post-tensioned parking structure beam that exhibits a long horizontal crack on one side of the 56 foot span beam, but not on the other side of the beam? I know that there are 7 kg hammers available that we have used in the past, but is there anything lighter, other than manual hammer and chisel? We want to remove anything that might break loose and fall on someone's head, but we do not want to chip out sound concrete that is not in danger of dropping off.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

(OP)
JAE - thank you very much.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

A mason's hammer and cold chisel (the old fashioned manual method) is an option we use as we approach areas of specific caution.

A Hilti TE 30 is our usual tool of choice for overhead or small horizontal work in sensitive areas. A Hilti TE 15 is a small tool too, replicating the manual effort of a mason hammer and chisel.

What caused the horizontal crack - incorrectly profiled PT tendon, corrosion? Obviously, the field personnel should be experienced in working with PT before they go chipping in close proximity to the tendons.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

(OP)
Thank you Ingenuity. I will look into the Hilti TE30 amd TE15.

We have done lots of PT design and repair and require that our engineer be present full time when this p.t. beam is chipped of the delamination. I don't know what caused the horizontal crack, but it is one or more of:

a) a previous repair failed at the bond line
b) rebar corrosion
c) tendon corrosion
d) tendon failure with the tendon failure exerting downward force on the top of a previous extensive soffit repair.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

(OP)
Ingenuity - how much do the TE15 and TE 30 weigh? I can't find their weight on the Internet.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

TE 30 is 8.8 lb

Go to https://www.us.hilti.com/drilling-%26-demolition/c... and click on Technical Data tab and it shows the weight etc.


Looks like TE 15 has been replaced, but it too is (was?) 8lb, but less impact energy.

A 8 lb electric hammer is pretty light-duty.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

But it is a DeWalt - HILTI eat them for breakfast smile

...and No, I don't work for HILTI, but we have a loooooot of HILTI tools.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

Maybe, but he wanted a light one...

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

At least a dozen times I have witnessed contractors successfully use 7kg jackhammers to remove concrete from the underside of post tensioned beams to expose the tendon sheathing. Success depends more on the operator of the jackhammer then the jackhammer itself and the points they are using. It greatly helps if A) the contractor understands what they are jackhammering into and B) the tendon locations are located with covermeter and marked. The good contractors will work to the side of the tendon locations and then work sideways towards the tendon location.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

(OP)
Thank you Ingenuity and hokie66 for the information on weights.

Thank you SkisAndBikes - - it is not so much the tendons that concern me, it is the 6" wide ledge on the side of the beam that supports the slab that bears onto this ledge (there is an expansion joint parallel to the beam) and I don't want to weaken this ledge when removing concrete below the horizontal cracks in the side of the ledge.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

That sounds like a bigger problem than you previously described. The crack is probably due to failure of the "expansion joint" to work. These type corbel joints are notorious for failure. I would suspect that the crack starts at the top inside of the corbel, proceeding diagonally down to where it shows on the face. So everything above the crack is loose. Have you investigated the original design of the corbel?

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

(OP)
A very good thought. That is possible for some of the cracks. There are horizontal cracks at different levels. I will look into the corbel design. The corbel is fairly deep and supporting a 13 foot span 5" thick slab of a parking structure designed for 2.4 kPa live load. It is always possible that the sliding coonection is not working right, particularly since this area of the beam has been repared at some time in the past (not by me) in which case I suspect they may not have put in a proper sliding bearing.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

If the bearing did not work as intended, and that is common, then in addition to repairing the cracked area, you may want to tie the two sections of structure together to prevent reoccurrence.

RE: Removal of concrete delaminated area from bottom of post tensioned beam?

(OP)
yes, right, hokie66.

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