The parking pad discussion got me thinking. How do I figure out the strength of my existing slab? Thinking of putting up a hoist, but need 4,000 psi concrete. Floor was poured in the late 90's and looks good.
The parking pad discussion got me thinking. How do I figure out the strength of my existing slab? Thinking of putting up a hoist, but need 4,000 psi concrete. Floor was poured in the late 90's and looks good.
Find somebody with one of these. Search for "nondestructive testing" and inspections. Somebody should be able to help you out pretty easily.
Also interested to find out. Similar situation, considering hoist... house was built/poured around 1990. No idea on material specs.
If I'm not mistaken the code was changed to allow 2500 psi in the late nineties or early 2000's. Prior to that, at least where I'm from, minimum psi for flat work was 3500. Also keep in mind that concrete continues to harden for many years, meaning a twenty year old slab will test harder than a 30 day slab.
Core drill a non critical spot. Take core sample to geotechnical lab for destructive testing. They'll crush it and figure out the strength for you.
Generally concrete is speced to be 3,500 psi but since no supplier wants to have to replace substandard material they generally err on the side of stronger. When I tested concrete in the late '90s for a living 3,500 mix would test out around 4,000-4,300 at 28 days. YMMV
The other thing to consider is how thick is the concrete?
Is the manufacturer's spec 4000#, or someone's opinion?
I've done several, and have never seen a manufacturer spec of 4000#. Some lifts require 6" thick concrete, but most seem to allow for 4" now.
If it needs 4000# 6", you probably don't have it. Buy a different lift.
4000# is pretty rare in residential.
Also rebar, it's size, and how it was laid out before pour, will affect the strength and stability of a slab.
Sorry Duke, but Schmit Hammer's are always optimistic. That (plus the fact it is less $ than preparing specimens and performing a destructive compression test) is why contractors generally want to use it. Experienced owners specify a cylinder or core be compression tested instead.
If you'd rather go for the overkill solution you can always cut out a couple chunks of the floor, dig down and out and pour footings.
In reply to Kenny_McCormic:
In other words, doing it the right way.
In reply to RX8driver:
Yeah, I do trust the engineering behind such and such slab being good enough, but gut feeling still says there should be a lot more concrete under such a thing.
KyAllroad wrote: Core drill a non critical spot. Take core sample to geotechnical lab for destructive testing. They'll crush it and figure out the strength for you. Generally concrete is speced to be 3,500 psi but since no supplier wants to have to replace substandard material they generally err on the side of stronger. When I tested concrete in the late '90s for a living 3,500 mix would test out around 4,000-4,300 at 28 days. YMMV
This.
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