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on the other end of the spectrum, did you know concrete can be used to demolish concrete?

dexpan is a special demolition concrete mix that, when poured into holes, expands at 18kpsi. it gets used when jackhammers and explosives cant be used, for example, in refineries and explosive atmospheres.



It's also useful if you want to do concrete demolition yourself using only hand tools. You drill holes, pour, wait for cracks, and then use a pick and hammer to remove the remaining chunks. Often sold as "expansive grout".


If you can drill holes you can use stone splitting wedges.

A lot of these high dollar modern miracles of chemical engineering are purely for use in situations where it's cheaper to just buy the $100/tube stuff than it is to try and get the approval to do something sensible. Basically you're paying to get around process tech debt.


Not in a refinery, or you have to buy weird/expensive non-sparking hammers and wedges. Aluminum bronze wedges are commercially available but the liability insurance is incredible so you're better off cutting your own (its a wedge, not a rocket engine...). It ends up being cheaper to use the expansive grout.


This is exactly what I mean by "paying to get around process tech debt"

Facility has a "no sparks" in buildings A, B and C rule. Rule obviously doesn't apply to contractors doing a ton of welding during a holiday shutdown. Non-contractors in maintenance dept want to fix some other crap at the same time. Sure they could try and get approval to use a jackhammer concurrent with the other work but in reality there's a 75% chance the safety department will intentionally stonewall until after the shutdown rather than set the precedent of a sensible exemption and the maintenance manager knows it so they buy the expensive grout.


Murphys Law implies the contractors will not be legally permitted onsite during operation so who cares what they do, but if you let the full timers play with jackhammers its guaranteed some idiot will try to use the jackhammer after operation resumes. So you'd need to do something like have the safety officer personally responsible for removing the jackhammer from the premises. Or renting it, perhaps.


Presumably dexpan has lower tensile strength so it can be disposed of easily? Or is the piece excavated and hauled away intact?


It expands in the holes you make in the to-be-destroyed concrete, cracking it. You can haul it off in chunks at that point.


The destroyed concrete, yes, but what about the dexpan? <Peregrine Took>


The dexpan is not a huge concrete structure, it's just a cylinder the size of the hole it was poured in.


Oh, I see, just a bore hole and hydraulic concrete. Sort of like the metal shims you see used in pre-industrial stoneworking.

I was picturing pouring it into a void for some reason.


The dexpan never existed as big pieces.


Won't it expand out of the holes you poured it into?


In some cases (particulary with modern, faster, formulations) it can, actually projecting (powder/smoke) out of the holes but it is not usually an issue.

When it happens is because the expansion is too fast (and consumes all the water available), making the grout itself fragile, with slower formulas, after the initial setting of the grout, you should water/keep the surface wet.

It is surprisingly difficult to find actual videos of it working (most are just a set of photos) because it is very, very slow (between 6 and 48 hours, usually), here is one from one of the many producers:

https://www.youtube.com/watch?v=CYAcHc9rP9o


Not if it hardens before it expands.


I've used that. Drill holes. Fill holes with gunk. Come back in the morning and the concrete is all cracked up. Silent and easy. Works great.




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