In this case, possibly due to watering plants near the patio.
The concrete in the photo is breaking up, so this has been going on for
quite a while. Redirect the water, improve the drainage, or find a way to
seal the underside of the concrete from water ingress
I never thought of that. You get very little water from the sky compared to
the north-east (where I live), so it would be expected that the salt
content of your soil would be high.
However, that salt can't go anywhere without water as the transport agent.
Somehow water is getting under the OP's slab and your driveway, and is
pushing the salt up and out. Or your concrete is really, really porous.
You have efflorescence and it appears have severely damaged the
Age of concrete? Was it sealed?
check these out...
It looks like something undesireable has been incorporated in the
concrete. There may be some embedded metal close to the surface.
Get a hammer and chisel and do a little digging to see if you can find
anything beneath. Eg a pipe or some such.
Dig out all the crap material, if there is nothing untoward, a repair
can be made.
It may be just a localised bad mix or something undesireable got into
the mix whilst it was being laid.
There appears to be some chemical activity more serious than simple
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