Posted: Jul 16, 2017 2:37 am
by Matt_B
Roman concrete is made from tuff, a volcanic rock that is fairly common in Italy but rare in much of the world. They had to use inferior substitutes in the far flung parts of the empire though.

Modern concrete is made from Portland cement, which can be manufactured from far more abundant limestone and clay, pretty much anywhere in the world. Unlike the tuff, it's chemically active, and reinforced concrete in particular suffers from corrosion of the metal rods, limiting its lifetime.