Crack Leakage

[ajk1]

Is there any crack width in a parking garage floor that there will theoretically be no leakage through the crack? For example, if it were theoretically possible to limit the crack width by design to a given width, say perhaps 0.1 mm or 0.05 mm, would surface tension effects, or any other effect be sufficient to prevent leakage? I know that it is not possible to limit all crack widths, but I am asking this as a "theoretical" question, to anyone who may be versed in the science of liquids. I am also interetsed in what your observations with this are in parking garages - have you found that very narrow thru slab cracks do not leak? My opinion is that any through the slab crack, no matter how narrow, will leak, particularly when the car wheels traverse the crack and prthaps push water down into it.

 

[a2mfk]

Concrete without coatings or moisture barriers is permeable without any cracks.

 

[oldestguy]

I have a diesel fuel filter funnel that will prevent water from passing. Screen size is 149 microns, stainless and coated with Teflon. For what it is worth. Don't forget that concrete has the pore sizes such that it will act like an osmotic membrane. Put salt (almost any salt) on one side and water will migrate there. That explains why floors coated with a flooring which is glued down comes loose. Concrete, having dried some first, carrying "salts" to the surface, has an imbalance of salt concentrator then carries water from below to the top higher concentration where that flooring is broken loose. Those pressures can be many inches of water pressure. Guess that doesn't help much, does it.

 

[ajk1]

a2mk - I know about concrete permeabilty, having spent a good deal of my career on it, but that was not the question. If stainless steel reinforcement is used, concrete permeability is not much of an issue. Leakage through cracks though would still be an issue (see CSA Standard S413 Parking Structures, for discussion of the leakage issue and why it is important, as distinct form permeabilty and reinforcing corrosion).

Oldestguy - the information about the screen size is very interesting.

Thanks to all. much appreciated.

 

[racookpe1978]

I'm not going to specifically answer the original question, but want to remind you that "soak time" and "soak pressure" and "material crack thickness" will be almost as important as "crack size" in this function.

The filter above has a long soak time (time for the non-evaporating fluid to remain in contact with the surface), but a low soak depth or soak pressure. On the other hand, the filter will be very, very thin (one fabric diameter thick) and that fabric is a round diameter smooth surface that encourages flow between filter strands, not a concrete "crack" that would have substantial length with a large amount of roughness. Any "ponding" on the concrete will dramatically increase the "soak time" - but if the standing water runs off, and the remaining surface tension held water can evaporate quickly, then you'd have almost no leakage even with cracks.

If it is critical, use a primer and a flexible concrete paint. Eliminate completely ALL standing water.

 

[ajk1]

racookpe1978 (Nuclear) - Thanks for that information. Very interesting. But a paint is not going to do it because it will relatively quickly wear off. Even the 60 mil dft polyurethane traffic topping waterproofing membranes that are routinely used in parking garages wear thru in the turning car areas. Our thoughts were more along the lines of whether the surface tension would hold the water from leaking thru a narrow crack. My feeling is that the car tires traversing the crack would break the surface tension and the crack would leak, but I don't know for sure.

 

[oldestguy]

On the fuel funnel filter, the test of the filter integrity is just fill it with water. That test means the outside of the screen is air, so there is an air-water interface. Whether this screen filters out water from the fuel, then may be a question. I wonder if the fuel-water interface works the same. For cracks in floor, if the floor is wet, at the crack there is no air-water interface and thus no surface tension there.

 

[dik]

OG... the adhesion of water to teflon isn't there, and a much coarser screen size would likely keep water from passing... The surface has to be wetted, ie the force of adhesion is greater than the force of cohesion...

Dik

 

[Ron]

ajk1....ACI 350 limits crack widths for leak serviceability to 0.010" This is for environmental structures; however, water leakage is water leakage.

Check Gergely-Lutz relationship also....I think it is less conservative.

Also, make sure cover is at least 2" as crack width decreases with depth (shrinkage cracks)

 

[Compositepro]

Concrete is hydrophillic, meaning that absorbs water. It's surface energy is greater than that of water, so water will spread out rather than bead-up. Thus a crack in concrete acts as a wick. Contact angle is a quantitative measure of this effect. Hydrophobic coatings like silicones, paraffin, oil will change this. A screen that is wetted by diesel will not pass water droplets. Teflon coating is not required.

 

[ajk1]

Ron - the Code equations for crack control parameter "Z" are in fact based on Gergely-Lutz. They correspond to permissible crack widths of 0.013" and 0.016" for exterior and interior exposure respectively. Of course there can be great variation in actual in-situ crack widths, even for the same design.

I am aware of sanitary structure design crack control requirements, but I believe that they may be based on the concept that a small amount of leakage is ok. That would not be the case for a parking structure, where the lime contaminated leakage water can damage vehicle finishes, as well as resulting in unsightly stalactites hanging down, and staining of the slab soffit.

As for the other discussions, I am afraid they are getting in over my head, and in any event are difficult for me to apply to a parking gaarge, as required by CSA S413 Parking Structures".

I was hoping someone would say that they have seen narrow thru-slab cracks in parking structures, that show no sign of leakage, or vice versa. Maybe the best thing is for me to go look at a garage, but the snag is that virltually all garages in my area now have a waterproofing membrane.

Thanks everyone for the comments to-date. Much appreciated.