Post-tension Cable feedback

So, I believe this is an exposed post-tension cable in this parking deck.

Does the exposure of this cable and visible surface rust substantially reduce the reliability of this cable? I have concerns this cable may be compromised. Any feedback helpful. Thanks.

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I don’t see how it could not affect the integrity of the cable if it is tension cable. It is not meant to be exposed and/or driven over. If nothing else it will be a potential hazard to customer’s tires in the near future.

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Yeah, it’s compromised.

You’re clearly into Structural Engineer territory here.

The owner has some options for PT cable rust including injecting grease:

See also

And my favorite basic engineering topic explainer on YouTube:

Now what evidence do you have that these are PT cables? Is there any sign of a duct or conduit that the PT cable tendons were placed into? Could this be regular rebar, not the PT tendons?


First, thank you for that information. I will read and watch it in a moment.

To answer your question, yes there was conduit. The photo is not great but there is the conduit (or a sliver of it).

Ok, that nails it. A stranded steel cable inside conduit through a concrete structure like that is a post-tension cable. The open conduit will allow water to get in, greatly accelerating rust on the cable.

As you know, failure of such a cable can be dramatic… tens of thousands of pounds of tension.

I think I will use this graphic in my report. Thanks!


The issue is NOT the rust you see. The issue is the water entering the conduit and rusting a point (probably a low spot) out of view. Thus, the process of carefully drying the cable, then injecting grease, and maybe adding zinc for anode/cathodic protection.


There were areas the re-bar did not have good cover as well. Things are adding up on this deck. This is all great information which will help elevate the issues in the narrative.

Back to the conduit and cable, I suppose mechanical wear from vehicles is not helping either. There is a reason why the cable became exposed, either lack of cover or wear or both. ( I would hate to think this was missed during install 22 years ago)

For future reference:

It’s not ‘cable’, it’s called ‘stressing steel.’
It’s not ‘conduit’, it’s called ‘sheathing.’ Also called ‘duct’ for multi-strand systems.
The complete assembly of stressing steel, sheathing, and anchorages is called a tendon.
The end pockets are called ‘stressing pockets.’
The route a tendon takes through the concrete is called a ‘tendon profile’. A tendon profile has a high spot and a low spot, although those areas aren’t called high or low spots. A profile’s shape also has elements of ‘drape’ with respect to the vertical deviation of the tendon’s path, and ‘eccentricity’ with respect to the centers of gravity of the concrete and the tendon at any point along the profile.

Your parking garage appears to be a single-strand (or mono-strand) unbonded tendon system, but that needs to be confirmed. The primary defect is insufficient concrete coverage over the tendon, resulting in mechanical failure of the sheathing, and subsequent corrosion of the stressing steel.


Thank you for the mountain of useful information.

I apologize for the poor quality photo. It is actually multi-strand which cannot be seen in this photo. Based on the exposed radius, I suspect the steel is approximately 1" diameter.

I have a question about lack of cover. Dismissing the corrosion issues or possible impact damage for a moment, does lack of cover contribute to potential mechanical failure?

Thanks for that. I rarely see PT slabs, and when I do, this will help me not to sound so stoopid in my report!


Lack of cover will lead to mechanical damage to the sheath, either from weather or rolling vehicle loads. Once the sheathing is breeched, corrosion starts on the stressing steel. It is corrosion to the stressing steel that will ultimately lead to failure of the stressing steel.


How would you get wear, on concrete, without deliberate abuse?

Where was the damage relative to car travel paths? Can U go back and get better close up and context pictures?

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They are in a parking space (see photo). At least one is in the path of travel.


The photos are, ahem, a bit hard to interpret for those of us who have never been there. I see some evidence of pitting, which would make sense if the duct was just barely covered with concrete on the day of the pour, but later did not “wear” out but tire pressure or whatever cracked the remaining thin concrete and exposed the duct.

Are you able to go back and take a progression of context, framing and macro/detail shots?

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I will not be going back. However, here is the original photo which has greater details. If you download the photo, you can zoom in an out and see things clearly.

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All good points. Without a time machine it will be difficult to determine. I have a theory.

A few other locations, rebar was also visible on the parking surface, almost all of the exposed rebar was clean…meaning it did not the typical spalling I am accustomed to seeing. The deck has patterns consistent with pressure washing. I think they blew off all the loose/cracked concrete around the exposed steel and even exposing it further. I found the spalled concrete remaining in only one location.

That is definitely a stressing steel cable, and not rebar.

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Thank you. In the subsequent photo’s in post #17 we have rebar. I am going to separate the stressing cable from the rebar in my narrative.

In the photo there are two bits of steel running parallel with a major axis of the structure. And something in the middle. Is that a bit of loose duct? Attached or lose?

I’m curious how you got this job, and how far it is from your home base.