Routing and Sealing overhead cracks

[IsaacStructural]

Just looking for general opinion. On flat plate concrete parking structures or similar, sometimes I've seen shrinkage cracks on the top and bottom of the slab. On the top surface, I generally recommend sealing the slab, and routing the cracks to 3/8" and installing an elastomeric filler over a bond breaker tape. On top of this a traffic membrane could be installed as a Cadillac solution, albeit one that may make for additional maintenance down the line.

I've seen some reference to routing and sealing cracks like this on overhead cracks, what is the logic of this, is it a purely aesthetic decision? Cracks on the upper surface tend to be exposed to moisture, de icing chemicals etc, while as best I can tell, the cracks on the bottom surface are points where moisture leaves the slab. Does it make sense to close these off, trapping the moisture inside, or forcing it to find a new exit point?

Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[IsaacStructural]

Bump.

Anyone have thoughts on this? Did I drop this in the wrong Topic?

Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[JAE]

IsaacStructural - If you have future moisture exposure above, I think your point about trapping water in the cracks is valid.

The only downside would be that - with cracks you introduce oxygen into the inside of the section. More oxygen plus water = excessive rusting of reinforcement.

But if you adequately seal off the top, perhaps you won't have moisture coming down from above.

 

[SlideRuleEra]

IsaacStructural - The potential problems you mention can be minimized by sealing cracks to full depth by injecting epoxy under pressure. This can be performed from one side of a slab, even if it is overhead. We used this procedure for structural repair of cracked cast-in-place columns several years ago. There are a range of epoxy compounds of various viscosities that can selected for differing conditions.

Here is an ACI summary of the procedure:

http://www.concrete.org/general/RAP-1.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[IsaacStructural]

Thank you both.

SlideRuleEra,

I've seen epoxy injection like you describe for columns, beams and other structural cracks, but I don't know if it is warranted in this case, the cracks I'm observing are tight shrinkage cracks, many with minimal or no signs of water penetration. Epoxy injection for all the shrinkage cracks of a parking deck seems like it might be unnecessary. This is why I'm considering routing and filling them from above and having the surface sealed and covered with a membrane to reduce any future water penetration.

Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[JAE]

You might consider a traffic bearing waterproofing system - (go here:

http://www.neogard.com/Literature/AutoGardT/AutoGardT.pdf)

There are pros and cons to this as turning wheels can wear down the coating.