Speaking of density, can concrete float?
There is a ship off of the coast of Galveston, TX on a sandbar. It is made of concrete. This is the S.S. Selma and it was launched in 1919. It was someone’s home off of the coast until the hurricanes hit a few years ago forcing the man off of the landmark.
Concrete can be made to float if it is shaped like a boat. A boat-shaped or hollow object will displace a volume of water greater than the actual volume of solid material in the object. The object is said to be “buoyant” when it floats due to low density.