Xist -- Found this:
news.mit.edu: Riddle solved: Why was Roman concrete so durable?
Now I want to make something out of concrete. Importing pzzalano would be difficult but this is just changing the order of mixing the ingredients. Worth making test ingots?
The only thing I can think of that I'd want made out of concrete would be a ferrocement pontoon boat [hull]. The reason being I saw this video on
Screw-Propelled Vehicles: Surprising Advantages in Warfare
The unsurprising disadvantage is that you could sink one with small arms. So I propose that the helical screws be a ballast tank. Flooded, it would sink onto the displacement hull. But blow the ballast and it would rise up like a hydrofoil and go forward and back, tank turn and crabwalk.