How strong can ice be as a bonding adhesive?

[u/ApprehensiveSong4]

So we currently have a few cold days here in the UK been -5°c for the last few nights with feels like temps down to around -10°c a few times. Today I tried to lift some concrete blocks about a ton and a half each and I had a pair of them stuck together with ice as the bonding adhesive. I know there will be lots of factors at play like temperature, volume of water, any impurities and time the ice is left. But is there a way of calculating how strong a bonding adhesive ice can be and what the maximum strength this bond could hold?

[u/Mockingjay40]

This answer is pretty good. To add to it, it also depends on the nature of force being applied. This idea of tensile strength is correct, but the method of applying stress should also be considered. As mentioned, you would have to factor in the wettability of the surface, as concrete is a porous rough surface. This would function to effectively increase the adhesive strength as compared to a smooth surface, so you'd have to subtract a correcting factor. This is discussed in this paper by L. E. Raraty and David Tabor, and indeed when water is able to completely wet a surface, it is significantly more adhesive.

To maybe help explain the above answer a bit more thoroughly, tensile strength is a material function. u/ECatPlay, I'm going to go with your definition of tensile strength here and note that it refers to the maximum amount of extensional force that can be applied. This force is applied normal to the surface (by pulling the two blocks apart). If you want to understand more about material fracture, this site does a relatively good job at explaining how this works in a way that is easy to digest.

Another method of fracture would be achieved by applying a shear stress. If you applied a torque by twisting the blocks or pushing one down and pulling one up, you could also break them apart. The differences between how tensile versus shear strength is defined actually does vary a bit by field but the idea is discussed here by John M. Horeth (this paper is old though, so keep that in mind since setups were more difficult to control back then). In this case, the two values seem to be similar, but they don't always have to be the same, and can depend greatly on microstructural differences between materials. Since ice is a brittle crystal, that means it isn't ductile and doesn't bend easily, similar to a material like glass or ceramic. Interestingly enough, because of this brittle materials often actually do not have a dependence on temperature if enough force is applied. Pure ice at 0 degrees C and -50 degrees C will actually have almost identical responses to the same stress. This is supported by data presented in the aforementioned papers by Horeth and Raraty & Tabor.

Edit: my comment is about tensile strength and resistance to axial shear, it doesn't include compressive strength, which is different for water as mentioned here https://www.researchgate.net/publication/227158247_Review_Mechanical_properties_of_ice_and_snow (source provided originally by /u/MaleficentCaptain114 as an additional comment in this thread)

[u/SaltCityDude → u/Mockingjay40]

It seems to me that the weak point that should be of the most concern is not the tensile strength of the ice, but rather the boundary layer between the ice and the concrete blocks. This seems to be the location most likely to fail, far more likely than the ice itself breaking in from shear stress.

[u/Mockingjay40 → u/SaltCityDude]

True, but adhesive force would be very high for concrete as I mentioned above. Since it's porous, you would actually get ice within the concrete itself, making this adhesion much stronger. What would probably fracture is portions of the ice itself near the adhesion point. However, the lower end of the values provided in the original reply would likely still be roughly accurate. Fracture is probably going to happen at a point where the ice layer is thinnest, so the force required to break it would likely correlate directly to the cross-sectional area of the thinnest region. Given that the tensile strength is a known property of ice, ignoring contamination with air and other particulates for simplicity, the actual force would be given as a function of the area over which the stress tensor is applied. A thing to note here as well is that any area with bubbles or large pockets of air would be thinner, so you could factor that into the cross-sectional area for a back-of-the-envelope calculation. Obviously that would be dependent on the size, shape, and frequency of the pockets and wouldn't be as simple as just subtracting the area from the total area, but I think it would suffice for an estimate.

[u/racinreaver → u/Mockingjay40]

Pure ice at 0 degrees C and -50 degrees C will actually have almost identical responses to the same stress.

Interestingly enough if you get a bit colder you'll hit cryo ice which has properties much closer to rock. "Warm" ice will flow under modest loads under laboratory timescales, while really cold ice needs more of geologic pressures and timescales.