Looking for High (relative) tensile strength very low weight cementitious material 2

[cajone5]

As the title says, I'm looking for a material with the following characteristics...

1. Cementitious material
2. Light weight (<60 pcf)
3. Low compression strength < 1000 psi
4. High relative tensile strength

I can find materials satisfying 1, 2 and 3, but unfortunately cannot find any information on tensile strength in these cases, or, at least, not promising information. Does anyone know of a cementitious material that possesses these properties? It would be used in a slab on grade application.

 

[JedClampett]

If you were to tell us the application, we might be able to help. But your description is asking for something that doesn't exist. If it did, we'd be building skyscrapers out of it.

 

[bowlingdanish]

Get some low strength cement concrete, replace the aggregate with recycled foam, and cast in a heap of Aramid fibers?

What possible application could this have?

 

[structSU10]

concrete compressive strength is tied to tensile strength - see the code for modulus of rupture.

 

[cajone5]

Thanks for the responses. I will say, I don't believe we'd be building sky scrapers out of 200psi material... but hey, to each their own.

What I'm after is a light weight topping slab. It needs to have a low compression strength for various reasons but the goal is to find something where tension is not tied to compression strength (ex; not 7.5 sqrt f'c). I think the fiber reinforced foamed concrete (cellular concrete / etc.) is probably the closest thing. To top it off I'd prefer it be brittle in tenion (but also strong) but at that point I think I'm asking to much.

In a bit more detail, the application is a thin (<2") topping slab on grade for a very lightly compacted fill material that itself has a low compression strength. The topping slab needs to resist uplift from high winds though so it needs a reasonable tension strength since it has a low mass. At the same time, it needs to be weak in compression (< 500 psi likely) so that it can still be easily penetrated if something heavy is placed on top of it. A bizarre application to be sure and why I'm seeking any advice on such a material. Cementitious materials are notorious for poor tension performance, especially light ones with low compression strength. Just seeing if something exists that is against this typical trend.

 

[racookpe1978]

Might look at a composite asembly: A weave of plastic fiber, then the foam-filled concrete as above, then a cover weave of the lightweight plastic again.

Short fibers inside a foam-filled concrete won't contribute much to tensile strength. Some certainly, but not too much.

 

[BUGGAR]

Tightly woven cable blasting mats that we used in rock quarries would work if you used aluminum cables for lightness and painted on some elastomeric coating to fill open spaces. If you need the cementitious, sprinkle on some sand. Or put the cable mat over an elastomeric sheet.

 

[bowlingdanish]

Is this some elaborate eng tips troll?

the application is a thin (<2") topping slab on grade

that's too thin

very lightly compacted fill material

compact the subgrade

The topping slab needs to resist uplift from high winds though so it needs a reasonable tension strength since it has a low mass

that just doesn't make sense

it needs to be weak in compression (< 500 psi likely) so that it can still be easily penetrated if something heavy is placed on top of it.

neither does that

I don't mind the philosophical discussion about materials though.

 

[cajone5]

It really is a bizarre application that I can't discuss in detail. Essentially the slab needs to be frangible (brittle/cimentitious) and crushable (low compression strength) for one set of demands but also has to resist some relatively high wind demands through flexure over relatively short spans (2-5 ft). The fill material needs to be lightly compacted and low strength because it also needs to be crushable for this application (fill is already sorted out). The thin cover is intended to be a monolithic (with the exception of control and expansion joints) pourable thin slab system that is sealing the fill against weather effects (along with a topping "seal coat" for moisture). If I could find a low density low strength "concrete" material where the tension strength was higher than typical concrete relative to the compressive strength that would solve my problem. The issue is I'm not sure one exists.

I'm currently looking into...

-- Foamed concrete
-- Cellular concrete
-- Low density CLSM

These all give me low density, low strength, frangible/brittle behavior and the ability to be cast as a thin slab but unfortunately they do not offer much in terms of tension strength relative to their compression strength (typically 10-15% direct tension and 25% flexural tension). Just trying to see if there's something out there that might be similar but have improved tension response.

 

[bowlingdanish]

Wind pulling up on it and weight pressing down on it will both put the slab into flexure (and shear). So you would need an anisotropic material that is strong in tension at the top face, and weak in tension at the bottom face. You would also need it to be good in shear pulling up, and weak in shear down, so it can punch through. I'd guess you'd basically need to go to a molecular level to achieve that. I bet a team of material scientists and a lot of funding could do it though. But it's not going to be cement.

 

[IDS]

Ultra High Performance concrete (such as Ductal) has very high tensile strength (for a concrete). If you added sufficient expended polystyrene to achieve your density requirements, it's possible that it might retain sufficient tensile strength for your purposes, with compressive strength also reduced to what you need.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[cajone5]

^^^ Excellent thought. That is the idea of what I'm after. I will have to research to see who (if anyone) offers such a thing.