Roman concrete secret and cement-based marine structures

[rwatson]

The sub was made by students at the TU Dresden for the 2002 german concrete canoe regatta. It's a two person human powered sub. 10mm carbon-concrete shell. Not a lot on the web but this sites have a photo each. The big yellow ugly thing is the sub.
Potsdam 2002 - Beton.org https://www.beton.org/inspiration/betonkanu-regatta/historie-sieger/archiv/potsdam-2002/
Die Kanus http://www.pjehle.de/BB/Regatta/Die_Kanus/die_kanus.html

Thanks. found it.

 

[rwatson]

Thr volcanic ash the Romans used is called pozzolana or pumice. It is used in modern Portland cements up to 3% as an inexpensive filler in areas like Greece where pumice costs less than cement clinker. The pumice is mostly mined in Giali between Nisyros and Kos as well as Santorini. Southern Italy also has readily available pozzolana.

You can also get pozzolan from other sources - ag. The FlyAsh from coal power stations. Thats the more common source for Ferrocement yachts.

The article discusses the adavantages of the two types
Natural Pumice Pozzolan Significantly Improves Concrete Performance http://www.hesspumice.com/pumice-pages/pumice-uses/pumice-pozzolan.html

 

[ScottK]

Basalt Mesh and or Re-bar is the latest and greatest. Basalt Mesh Geo-Grid reinforcement is better than steel https://basalt-mesh.com/

Basalt Rebar reinforcement is an alternative to steel and fiberglass for reinforcing concrete https://basalt-rebar.com/

 

[rwatson]

The sub was made by students at the TU Dresden for the 2002 german concrete canoe regatta. It's a two person human powered sub. 10mm carbon-concrete shell. Not a lot on the web but this sites have a photo each. The big yellow ugly thing is the sub.

Hmmm - not quite a sub. It has no provision for human life support, I presume the scuba divers sheltered behind the open cockpit, and pulled levers to empty the two flotation pods on each side to surface. Still. it was very innovative and a bit more interesting than just some sort of boat.

 

[dsigned]

Hello everyone, I'd love to hear your opinions on this recent discovery by Utah University researchers: How seawater strengthens ancient Roman concrete | UNews https://unews.utah.edu/roman-concrete/

Basically, they think they figured out the secret of Ancient Roman concrete's durability in the face of thousands of years of exposure to sea water. It turns out that the use of specific volcanic ash in the cement mix allows for a porous structure that grows interlocking tobermorite (a very unusual mineral) crystals inside of its pores, from elements present in the sea water. Basically, Ancient Roman concrete accretes more and more minerals over time simply by being exposed to (alkaline) sea water, reinforcing it over time instead of corroding it away. Though it has a lower compressive strength that might have interesting uses in ferrocement builds ?

Technically, they've had the "secret" to Roman concrete for a while. It's marketed as "reactive powder concrete", and uses a different chemistry to portland cement. It's advantages are that it can be combined with Portland cement to make a concrete that's stronger than either would be by itself. It's also capable of being impermeable to ionic penetration. In other words, seawater won't leach into it. Here's an example of some of the stuff available to purchase:

Silica Fume, White, 50lb bag - Fishstone - Concrete Countertop Supplies http://www.concretecountertopsupply.com/Item/SilicaFumeBrightWhite50lb

 

[dsigned]

I doubt there are too many good, cheap fibres to add to a concrete mix, when asbestos was banned, the best they came up with was celluose fibres, and that is no good exposed to water.

Non-reactive fiberglass and basalt are both options.