Titanic tourist sub goes missing sparking search

[Gone for diving]

Another promising underwater material is reactive powder concrete, but it will need lots of testing and experience in unmanned applications first, before going to manned use at really high load factors.

Had to look that up.

Would it be light enough to float a sphere or something similar?

Seems like they should make boats with it first,

 

[Akimbo]

Another promising underwater material is reactive powder concrete, ...

The Naval Civil Engineering Laboratory in Port Hueneme, California did a lot of work on concrete spheres for external pressure vessels in the late 1960s. I visited there just before joining the Navy. They had a bunch of imploded hemispheres in the yard outside the pressure testing building.

Like glass, concrete has high compressive strength but like carbon fiber is not a homogenous material. Glass hemispheres have been used for deep ocean scientific instruments since the early 1960s.

It was never clear to me why a Civil Engineering Lab associated with the CBs (Construction Battalion) was doing this work but it was pretty interesting. My impression was that they wanted to use them more for long-term unmanned deep sea buoys and instrument housings.

I used to work at a company that built deep submersibles.

Which company (ignore if you prefer not to say)? There aren't that many.

 

[Blasto]

Had to look that up.
Would it be light enough to float a sphere or something similar?
Seems like they should make boats with it first,

About as dense as aluminum, but can get to steel-like compressive strength if cured under heat and pressure. Not as great in tension, so it can't compete with carbon for surface boats. But they're starting to use it for offshore structures and have designed underwater housings for 3,000-6,000m depths.

The big deal is how it's much easier to cast a thick hull out of a concrete-like material, even with extra-special handling and curing, than to bend and weld one out of metal plates, especially avoiding any weld defects. So one can use spherical curves, complex shapes, extreme thickness, and still keep the cost low.

The Naval Civil Engineering Laboratory in Port Hueneme, California did a lot of work on concrete spheres for external pressure vessels in the late 1960s. visited there just before joining the Navy. They had a bunch of imploded hemispheres in the yard outside the pressure testing building.

A lot has changed since then. In the 1960s, state of the art concrete was 6-10 ksi, and still included coarse aggregate and steel rebars. Now it's dust-sized aggregate, <10% water (not workable by hand at all), reinforced by thin glass or carbon fibers, and gets to 30-45 ksi in the field and 50-100 in the labs.

It's not going to beat titanium, but has already passed high-yield steel and aluminum. CFRP is an even stronger option, but it's even more expensive and doesn't do as well in seawater.

 

[Wibble]

Had to look up KSI:

ksi (unit), kilopound per square inch, a non-SI unit of stress or pressure

Pound per square inch - Wikipedia

en.wikipedia.org

 

[Gone for diving]

About as dense as aluminum, but can get to steel-like compressive strength if cured under heat and pressure. Not as great in tension, so it can't compete with carbon for surface boats. But they're starting to use it for offshore structures and have designed underwater housings for 3,000-6,000m depths.

The big deal is how it's much easier to cast a thick hull out of a concrete-like material, even with extra-special handling and curing, than to bend and weld one out of metal plates, especially avoiding any weld defects. So one can use spherical curves, complex shapes, extreme thickness, and still keep the cost low.


A lot has changed since then. In the 1960s, state of the art concrete was 6-10 ksi, and still included coarse aggregate and steel rebars. Now it's dust-sized aggregate, <10% water (not workable by hand at all), reinforced by thin glass or carbon fibers, and gets to 30-45 ksi in the field and 50-100 in the labs.

It's not going to beat titanium, but has already passed high-yield steel and aluminum. CFRP is an even stronger option, but it's even more expensive and doesn't do as well in seawater.

Very Cool.

Yeah concrete in tension....

Any floors we pour I use fiber in the concrete. Its amazing how much stronger it is.

 

[Akimbo]

A lot has changed since then. In the 1960s, state of the art concrete was 6-10 ksi, and still included coarse aggregate and steel rebars.

As I recall, these experimental spheres were cement and a very fine aggregate, no rebar or rock. They were about 48" in diameter with wall thickness in the 2-3" range. I think they epoxy impregnated them due to water intrusion.

 

[Blasto]

So t

As I recall, these experimental spheres were cement and a very fine aggregate, no rebar or rock. They were about 48" in diameter with wall thickness in the 2-3" range. I think they epoxy impregnated them due to water intrusion.

So they were working on the same things then, figures that lab experiments are always ahead of actual use.

One major change was the addition of superplasticizers, which allowed for ultra-dry mixes, impossible to flow into shape otherwise. New generations of UHPC/RPC contain partially-reacted cement, and when water gets into any microcracks, the cement reacts and reseals them. So it's best left unsealed, which helps for underwater environments.

 

[broncobowsher]

So t

So they were working on the same things then, figures that lab experiments are always ahead of actual use.

One major change was the addition of superplasticizers, which allowed for ultra-dry mixes, impossible to flow into shape otherwise. New generations of UHPC/RPC contain partially-reacted cement, and when water gets into any microcracks, the cement reacts and reseals them. So it's best left unsealed, which helps for underwater environments.

I'm just thinking of all sorts of new ways that things can go wrong...
Let me try and put thoughts into words. Microscopic air passage (microcrack as you refer to them). Add pressurized water. The air compresses to a dead end at the end of the passage. The water finally hits a bit of cement mix and it seals the passage. Surface, lose the outside pressure. Now there is a pocket of highly compressed air sealed inside concrete. Now the concrete around that pocket is under severe tensile stress as the air is pushing out. Concrete isn't the greatest at tensile. That's not the end of it either. Salt water now trapped in that passage. A very slow drying out as the water eventually leaves but the salt crystals stay behind.
I'm also thinking of 25 years ago when the designer concrete had specs of surface spalling, which was created by sprinkling rock salt on curing concrete. So I remember that salt is not good for making regular concrete cure well, not sure how that plays into the special mix.

 

[HalcyonDaze]

I'm just thinking of all sorts of new ways that things can go wrong...
Let me try and put thoughts into words. Microscopic air passage (microcrack as you refer to them). Add pressurized water. The air compresses to a dead end at the end of the passage. The water finally hits a bit of cement mix and it seals the passage. Surface, lose the outside pressure. Now there is a pocket of highly compressed air sealed inside concrete. Now the concrete around that pocket is under severe tensile stress as the air is pushing out. Concrete isn't the greatest at tensile. That's not the end of it either. Salt water now trapped in that passage. A very slow drying out as the water eventually leaves but the salt crystals stay behind.
I'm also thinking of 25 years ago when the designer concrete had specs of surface spalling, which was created by sprinkling rock salt on curing concrete. So I remember that salt is not good for making regular concrete cure well, not sure how that plays into the special mix.

I was more thinking that 1) concrete is not known as being a ductile material, so how it responds to repeated pressure cycles is critical, and 2) you will have penetrations for hatches, viewports, electrical connections, etc. that will require interfacing with different materials and introduce similar concerns about how those interfaces change under pressure.

 

[Russjstewart]

NYC Explorers Club Used Global Reach For Doomed Titan Rescue

By Amanda Gordon and Guillermo Molero (Bloomberg) –When word reached the Explorers Club that the Titan submersible had gone missing — with two of its members on board — the venerable...

gcaptain.com