Guardrail Pocket Failures 1

[Guastavino]

I've never been a big fan of the Guardrail embedment detail for exterior applications. This is in a normal climate (some freeze/thaw, but not excessive). It is hot-dipped galvanized railing that is about 5 or 6 years old, embedded 5" into concrete below and grouted. I don't have the specs on what grout was used, but clearly this isn't working...anyone had success on a retrofit without replacement?

I'm thinking about having them chip out the grout, clean the steel and replace with an epoxy grout that isn't as permeable, then put a rain cover type piece over that to shed water...I don't like that much either, but it could be a temporary bandaid

 

[Guastavino]

Also, I think a root cause of issue is that the grout pockets hold water as they aren't flush with the concrete above, forcing water to constantly be in contact at the connection...but I still don't like this detail!

 

[dik]

Is the bottom capped so that water can be trapped? there should be provision in the detail to prevent a void space there should also be a hole at the bottom to drain water... Even a 1/4" hole can be used to flow in flowable grout. I've heard that water expands with a force of 2000 psi...

Ron: a classic example of your post embedment type of installation.

Dik

 

[Guastavino]

The bottom does not appear to be capped. Appears open, see below from shop drawing...I don't have original design documents showing designer's intent, just shops.

 

[XR250]

Do you think it was freezing water expansion or corrosion jacking that caused it?

 

[Compositepro]

dik, there is no limit to how high the pressure can get when water freezes. It depends on the containment and how it freezes. The worst case is when water freezes in a pipe progressively from one end to the other, in which case the water keeps getting squeezed into a smaller and smaller volume. The first part of the pipe to freeze will see very little stress and will not be participating in expanding as the water freezes.

A pipe that freezes from top to bottom across its diameter will radially expand uniformly along its length. In this case you can calculate the expansion pressure due to freezing.

 

[Ron]

dik....yep....seen thousands of them. Often problematic but certainly more load resistant (until it corrodes and fails!) than typical baseplate attachment.

 

[Guastavino]

I do think it was freezing water/corrosion jacking that caused it, but more freeze thaw. I hope the pictures are helpful too as we all consider this detail moving forward.

Ron, have you seen any good ways to do this or retrofit? Again, I'm thinking they chip out the grout, go back with a less porous grout and then put some sort of rain cover to try to keep the water from getting in/around the rail. It would only be a bandaid though

 

[dik]

CompositePro... thanks

Dik

 

[EdStainless]

I would guess that that the posts are beyond safe use.
Leaving them below grade created a bad situation.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Scratch3r]

I've run into this a few times on retaining walls and on guards at slab edges.

A better practice is to use a flush plate with embeds. You can weld to it later.

A side mounted plate for retaining walls is also good.

 

[Ron]

Guastavino....even if you could chip out and replace the grout, you have section loss from corrosion in the posts. These should be fully replaced or sleeved and welded at the bottom and extend several inches above the grout line. After sleeving, corrosion protection will have to be done, but will likely not be as good as the original hot-dipped galvanizing.

 

[Guastavino]

Does anyone have a good summary of the best locations for weep holes with guardrails? I would think that condensation could get inside the rail on hot/cold cycles, drip to the bottom of the pipe, likely not dry-up, and then freeze thaw from inside the pipe. Is that crazy talk?

 

[Guastavino]

I'm also thinking that a good way to make this detail work (the embedded post detail) would be to leave a 1/4" hole at the base of the rail, fill the base full with spray foam insulation (such as Great Stuff). That would prevent water from getting in. Then, either make the grout with a slight dome shape to shed water, or make the grout flush and put sealant around the pipe edge. I'm trying to think what problems that could cause...

That's a decent amount of extra work, but those guardrails in the photos are only about 6-7 years old.

 

[Ron]

If you seal weld the post top and bottom, it will prevent moisture inside....mostly.

 

[dik]

Does anyone have a good summary of the best locations for weep holes with guardrails

You can introduce a small 1/4" dia hole about 2" above the surface and can use this hole to fill the embedded part of the pipe with a flowable or non shrink grout. This will prevent water from freezing in the lower part and expanding. Have done that numerous times... same with exterior HSS columns... even if there is no chance for water to get in.

Dik