Stretch the concrete

[majo72]

I am planning to build a frame to place a tunnel greenhouse on. The greenhouse is 3x8 meters. I was thinking of building a mold 20x20 cm h/w around it. Would it work to fill this mold with, for example, 16/32 or 32/64 macadam (along with rebar) and vibrate down the concrete, alternatively layering concrete/macadam/vibrating to save work and money?

 

[BSOD]

20 x 20 is an extremely massive slab for a greenhouse. If you want to save money, make a smaller slab rather than mixing poor concrete.

You must mix the concrete in a mixer, you cannot vibrate down the concrete.

 

[Gabbe1]

The concrete as such already contains a large portion of macadam or ballast.

 

[Daniel 109]

Concrete already contains stone. If you want to fill the volume, you can add larger stones, but I don't believe in trying to fit it into macadam. However, if you are casting without reinforcement, you can "procenta" with stone gradually. If it is reinforced, it becomes more difficult.

 

[Taxture]

You can buy ready-made beams...
For example:
https://www.blocket.se/annons/halland/palkap_betongbalk_kabelkanaler_beg_stalbalk/99736192

 

[majo72]

20 x 20 is a really massive foundation for a greenhouse. If you want to save money, make a smaller foundation, rather than mixing poor concrete.

You must mix the concrete in a mixer, you can't vibrate the concrete down.

Yeah, the latter is obvious, but maybe you could manage with a much lighter construction as you say. I was mainly considering the size of the lecablock, but this will be stronger regardless.

 

[majo72]

You can buy ready-made beams…….
For example:
[link]

If they were a bit closer to home in northern Värmland, they would be interesting! It would have been a couple of trips with my unbraked trailer

 

[majo72]

Concrete already contains stone. If you want to fill volume, you can add larger stones, but I don't believe in trying to get it into macadam. However, if you're casting without reinforcement, you can "procenta" with stone gradually. If it's reinforced, it becomes more difficult.

By "Procenta," do you mean to alternate? Isn't that somewhat the same as I wrote? What happens if you vibrate together concrete with smaller stones, does the concrete weaken then? Larger stones would even look nice. I'll see if I can gather enough to make it sufficient.

 

[Snickarkirre]

I think you would benefit more from reducing the dimensions of the casting instead of adding stone by percentage. If you reduce the width and height to 15cm instead, you use 495 liters of concrete instead of 880 liters. That way, you save a few thousand kronor.

 

[z_bumbi]

Using stones in proportion is common in older constructions, but on such a narrow construction, including reinforcement becomes a bit of a puzzle.

When pouring a foundation/pillars for a barn or the slab in a stable, there was more space to dump in the stones that were available. Manure gutters and feed tables can make the construction in an older stable sometimes ridiculously thick, and with a meter of concrete, it matters less where the stones end up. However, the cost of cement became significant compared to the free stones.

If you want to use stones in a foundation for a greenhouse, I would, if there are piles of stones, consider building with them, but only because it could be fun to try. Concrete and Leca are much simpler.

 

[Manhunter]

War concrete contains a lot of stone.

 

[Huddingebo]

A 100-year-old rule of thumb I found in a construction manual was that you can fill up to 25% gravel stone in foundation walls and soles without losing too much strength.

But today with cheap transportation, I don't know if it would be worth it...

 

[z_bumbi]

What would be interesting is to see how old crushed concrete affects the strength, both as a replacement for crushed stone/gravel and as an extended percentage. It would be convenient and cheaper to be able to use concrete crushing.

 

[lodin92]

My experience both from mixing and breaking old concrete is that you can stretch the concrete incredibly much. When I've mixed concrete and it has spread out into a 4-5 cm thick layer on the parking lot, I haven't managed to crack it with the 6 ton backhoe loader. Despite pressing with the teeth on the bucket and with the rear wheels off the ground, there hasn't been the slightest crack, just small dents from the teeth. Had to lift it from the side, and when it's not firmly against the ground, it of course breaks easily. So if you have a good base, I would dare to cheat quite a bit.

 

[Snickarkirre]

The problem is not that they can't percent the concrete. After all, it's just a base for a greenhouse, so there won't be much load on it. But if you percent too much, the concrete might have trouble flowing everywhere, resulting in casting scars. It might be worth keeping in mind anyway.