Mix your own high-strength concrete!?

[nilhe1]

I'm about to cast a concrete slab for a table, a task that doesn't have to be particularly complicated unless you're like me and enjoy experimenting.

The idea is for the slab to be 20-25mm thick, 180x80cm.
I plan to reinforce it with a rebar mesh of 6 or 8mm iron with 150mm squares, and possibly a tied-on plaster mesh.

Initially, I thought of simply buying a bunch of bags of fine concrete and getting to work.
But since I now have fine sand (0.25mm) in sufficient volume and love to try new things, I'm considering mixing it myself.

I hope for feedback on the following thoughts for the strongest and most attractive slab possible.
- Portland cement + fine sand in a 1:2 ratio
- Rebar mesh with tied-on plaster mesh
- Plasticizer to reduce the need for water
- Agent to reduce air bubbles
- It will be mixed with a hand mixer and vibrated in the mold.

Is there anything I've missed to achieve maximum strength? Anything I've thought wrong or should do differently?
All feedback is gratefully received!

 

[C.Lundin]

You don't need high-strength concrete for a countertop. It is used in larger buildings and construction work. Just buy a couple of bags of expansion concrete and don't complicate things. But I would probably reduce the size of the mesh if you're only going to cast 25 mm.

 

[nilhe1]

You don't need high-strength concrete for a countertop. It's used in larger buildings and construction works. Just buy a couple of bags of expanding concrete and don't complicate it. But I would probably go down in size on the mesh if you're only going to cast 25 mm.

Oh, but I know I don't "need" it. But as I wrote, I would like to experiment and learn new things, hence the thread. Regarding the reinforcement mesh, the smallest I find is 6mm which doesn't need to be spliced to cover the area. The alternative is that plaster mesh might be enough, even though it feels way too flimsy...

 

[C.Lundin]

Oh, but I know I don't "need" it. But as I wrote, I like to experiment and learn new things, hence the thread.
Regarding the reinforcement mesh, the smallest I find is 6mm which doesn't need to be spliced to cover the surface. The alternative is that rendering mesh might suffice even though it feels too flimsy...

What are you aiming to achieve then? C50/60? C70/85? You won't achieve that with a mix made at home in the yard.

6 mm is probably the absolute max. But there's a big risk it will be visible.

 

[nilhe1]

Darn! C50 would have been enough, but I guess there are too many additives that the average person doesn't have access to.
I'll have to think it over again regarding this...

 

[C.Lundin]

Darn! C50 would have been sufficient, but I guess it has too many additives that the average person doesn't have access to. I'll have to think this over again regarding this...

Yes, it mainly requires additives but also to some extent admixtures. But you can still mix and play; concrete is fun! However, I would still argue that for the best result on a slab, you would probably get that from ready-made expanding concrete. At least it achieves the strength you desired..

 

[witten]

High-strength concrete requires a lot of cement, which causes it to set quickly and crack significantly, something that must be controlled with extra reinforcement.

You would likely be quite disappointed with the result.

 

[C.Lundin]

High-strength concrete requires a lot of cement, which causes it to set quickly and crack significantly, which must be controlled with extra reinforcement.

You would probably be quite disappointed with the result.

The heat development can be better controlled with slag instead of fly ash, etc. But it still sets quite rapidly...

 

[falkn]

Regardless of what you use, a thickness of 20-25 mm is too little on the board. I agree that expanderbetong is preferable.

 

[witten]

The heat development can be better controlled with slag instead of fly ash, etc. But it still burns well anyway...

Yes, the challenges are probably not as significant in such a thin slab.