Steel and ferro-cement re-bar suffers from the same problem - salt water. It is very hard on iron based metals as the rust corrosion can be severe.
If you replace the re-bar with fiberglass re-bar, you avoid the structural rust that plagues ferro-cement. If you change the concrete mix to reduce water permeability you further extend the life. Trade off as it is a minor cost increase but significantly extends the life of the craft.
TRUE. Though “being long lasting” was NOT a huge priority, as MOST cargo ships that supplied the UK & the USSR during WWII seldom made no more than 2-3 roundtrips before being “lost at sea”, due to storms, striking obstructions, collusions with other ships of the convoy, sea conditions or U-Boats.
Fwiw, I saw a period document from 1943 some years ago that said that a ship was “considered” a SUCCESS, if it made ONE round-trip to the USSR with the cargo/crew intact.
Yours, TMN78247
The concrete mixture contained smaller particles of metal and also a polymer of some type that bound the concrete and was also supposed to keep the structure from corroding
We used three types of metal fencing (screening)to frame out the hull and interior walls. The concrete had to be pushed through the screening by hand and then troweled off for a smooth surface. Never did see the boat launched.