I'm building a shed.
I've got a load of concrete blocks laid flat on the floor which I have been using as a hard standing for a Land Rover.
I've moved the Land Rover so I am now going to level the surface with crushed brick ready for a concrete floor for the shed.
I may, one day, want to restore a Land Rover inside the shed, so the floor needs to be reasonably strong to take the point load of a jack or axle stands.
So, I've got 3"-4.5" of concrete blocks, 2"-4" of hardcore.
Does 3" of concrete on top of that sound about right ?
What about mesh ?
I can carry sand, gravel and cement easily, but mesh will need a bigger trailer.
How important is it ?

By the way, I've got a lot of building work to do around here.
There will be a lot more questions after this one. 🙄

Get the mesh cut into bits, then wire it together?

Personally, I'd go for a bit more than 3" of concrete if you're putting a vehicle on it, that would be OK for a footpath, but not really for anything more. Personally, I'd double that, but that may be overkill.
And yes, mesh is important:

Concrete is strong in compression, but not under tension. So, if it flexes, like a slab with a vehicle on top of will do, it cracks at the bottom whre the flexing becomes tension. Steel mesh will prevent this to a large degree and hold it all together. This is why the mesh should sit closer to the bottom.

"Get the mesh cut into bits, then wire it together"
That's what I would do. Or more likely get it delivered, with my ballast and cement.

I could go on about this adinfinitum (I've got qualifications in concrete – Yawn!) but I won't…. 😉

Very, if you want it to last with a Landy parked on it!

Mesh will help mitigate the chances of cracking of the slab due to differential settlement.

It is unlikely that your crushed brick layer will be sufficiently compacted and more importantly equally compacted across the whole area of the floor slab to prevent at least minor amounts of differential settlement.

More importantly however is the base / underlying soil that you are laying your sub-base material on to.

Personally i would dig out everything soft until you hit a reasonable competent layer, add brick / stone fill (150 – 300mm) and compact with a wacker plate and then lay 150 – 200mm of mesh reinforced concrete.

That wont go anywhere fast.

A soft or poorly compacted underlying material will be the major factor in how strong your conc. slab will be and how badly it will be affected by differential settlement.

Won't the concrete blocks need breaking up before the hardcore goes on top?

MG-

In civil engineering reinforcement is used as concrete is poor in tension, to stop cracks propagating and to stop shear (think axle stand punching through). Whether or not your plan is sufficient is a "how long is a piece of string question". The answer is entirely dependent on how much abuse the floor gets. Rebar requires minimum concrete cover to stop corrosion damaging the structure; you're not planning on having concrete deep enough to easily accommodate rebar.

It's hard to be sure how to do a garage floor. Last year I helped a farmer pal lay one, maybe 4 inches over compacted hardcore. The concrete was professionally purchased, and included mixed in fibres to help make the concrete more resilient. So my suggestion is research that next – here's the first google result I found.

As said above your sub base is the key! However you do not need to go anywhere near 200mm in thickness for the concrete. I build industrial units and 175mm suffices plenty with one layer of a193 mesh. 100 mm to 125mm of concrete should be plenty with one layer of above mesh. If your cutting the mesh don't forget to allow for lap to the joints. Again in this type of op 200 lap should be plenty ie 1 square. Think of your finish also, before you lay. Power float, tamp etc

Sad Civil Engineering hat ON

This is why the mesh should sit closer to the bottom

Steel reinforcement is used to A: structurally reinforce & B: to prevent early age thermal cracking.

Your mesh should probably go in the top to stop the cracking when the concrete sets. (or you could slow the concrete setting process down, admixture, PFA etc)

This is purely an aesthetic thing, doesn't really matter if it cracks on the underside face

Unless of course your slab isn't going to be ground bearing.

BS8110 says minimum of 0.13% steel reinforcement to prevent early age thermal cracking, this equates to using A393 mesh in both faces of a 300mm thick slab. (A393 mesh = 10mm cross section bars at 200mm centres)

Sad Civil Engineering Hat OFF

Just chuck some rubble in there and cover it in 6 inches of concrete, it'll be fine.

Take that hat and throw it away ha ha. A393 is a ballache to handle and twice the price! And never use Pfa in anything you want to get a finish on prior to the early hours of the morning. Just a strong mix c35/c40, straight opc and no additives.

Yeh, wouldn't wear that hat for a garage floor tbh… just used to designing slabs for big heavy things…

What a lot of replies to one simple question.
If only they all agreed. 🙂
I'll be mixing the concrete myself as there's no chance of getting a truck anywhere near my place, I have to fetch everything myself by Land Rover and trailer.
Thinking about this a bit more, I hand mixed the concrete for my drive, and that's proper hand mixed, on the floor with a shovel, as I didn't have a mixer then, and that's lasted OK.
From what I remember, that's about 4" thick on hardcore and it hasn't cracked.
How about if I make it 4" at the thinnest so it will then be about 6-7" in places where the blocks aren't level ?
That should be stronger than what I've already got.

Yeah it's plenty thick enough at 4 inch. I would stick a sheet of mesh in it though, just to be safe! Mix it four and one using
3/4 ballast and it'll be sound! And if you want, cut the mesh to make it easier to transport just make sure you allow for the lap. Seemples 😉

Does it "need" to be concrete?

How about a resin bonded floor?

3".. what are you? A quantity surveyor?! More like 150-200mm

I reckon what you need is advice from someone whose laid a driveway, this guy might be able to help.

You can always spread any point loads with some mild steel sheet.

I wouldn’t bother with mesh – 150mm concrete on sand blinding on 150mm of hardcore on ground cleared of topsoil down to a solid base.

1 layer mesh
150mm concrete

job done!

You think this thread is boring? you should sit through my lesson about it!

You can always rely on a spammer to drag up an old thread. I was expecting an update from the OP on his cracked concrete!