Refill under car lift

[schmakita]

Hi, I have a car lift (recessed scissor lift) where the cutouts are a bit deep. I need to fill about 70 mm, what do you suggest?
Fine concrete? Fiber concrete? Structural concrete?
It's already quite thick and well-reinforced, so it's mostly to not lose lifting height.
But I guess a reinforcement mesh is reasonable to throw on when you're pouring anyway?

 

[Matti_75]

Raise it to the correct height and underpin with exanderbetong. Otherwise, you can cast with coarse concrete. Reinforcement is not needed since it should only take tensile loads and you only get compression when you have a cast slab underneath.

 

[RoTe]

Otherwise raise the lifts with steel spacers? There are, for example, square tubes 70x70x4...

 

[Kane]

Reinforcement is not needed since it only needs to handle tensile loads

Tensile loads?

 

[schmakita]

Raise it to the correct height and underpin with expanding concrete.
Otherwise, you can cast with coarse concrete. Reinforcement is not needed since it will only take tensile loads and you only get pressure when you have a cast slab underneath.

Good idea! I've seen others use that method, not entirely comfortable but why not.. need to think a little!

Otherwise, raise the lift with steel spacers? There are e.g., square tubes 70x70x4...

I've thought along these lines, and this should work well, but I still don't feel completely comfortable doing so. It feels (perhaps overkill) more solid to cast a proper base underneath.
What I was thinking was to place "spacers," like round steel pucks, of appropriate height under the mounting points (4 per platform or something like that), but then I thought maybe there should be support underneath the whole (scissor lift where one arm is hinged and one slides). Your method solves this, but still not entirely comfortable here.

---

However, I'm thinking it really doesn't matter which mortar I use, right? The original casting was done at the same time as the slab was cast, so it's good concrete and the guys who did it were good. So regardless, as long as I mix it somewhat by the book, there shouldn't be any issues! (We're considering C30+ with low wct and vibrating it)
The reinforcement was mainly intended to prevent cracking; the bearing capacity should already be 100% clear, and as you mentioned @Matti_75, there won't be any tensile stresses in this slab. It's just height adjustment.

 

[schmakita]

Prop it up to the correct height and cast beneath with expanding concrete. Otherwise, you can cast with coarse concrete. Reinforcement is not needed since it only needs to handle tensile loads and you only get compression when you have a cast slab underneath

Btw, when is coarse concrete preferable over fine concrete? I don't really feel like I have a handle on the difference other than knowing that there's a difference in how thick you can cast with each.

 

[Matti_75]

Btw, when is coarse concrete preferable over fine concrete? I don't really feel like I understand the difference other than I know that it varies in how thick you can cast with each.

It's really just the layer thickness that determines it. They usually have the same strength.

 

[Matti_75]

Tension loads?

Yes, or tensile forces if you're particular. The sole function of the reinforcement is to hold the concrete together where tension forces or loads occur.

 

[Kane]

Yes, or tensile forces if you're being picky. The sole function of rebar is to hold together the concrete where tensile forces or loads occur

Didn't quite catch your logic when you wrote this. Perhaps you didn't either

Rebar is not needed because it is only supposed to handle tensile loads

 

[Dan_Johansson]

Couldn't understand your logic when you wrote this. Maybe you don't either

The reinforcement should only take tensile loads?
I thought it was easy to understand?