Originally Posted By: SuperDave456
Rebar is known to rust inside concrete structures. Another reason why our infrastructure is crumbling.
The real problem is that Water stuff. H2O is just plain corrosive. They should ban it.
That would fix everything.
Check out some really old structures, versus some 30-40 year old ones.
Old concrete was milled very coarse due to prevailing technology, and just gets harder and stronger with time. The excess reactive material makes it self heal when crack develop (see old water towers and tanks with the white deposits sealing cracks).
Later, they discovered how to make cement much finer, and they achieved their 28 day structural ratings with much less active material...and that's about as strong as it ever gets.
These concretes aren't self healing to anywhere near the extent, and are more prone to carbonation, where CO2 from the air reacts with the concrete, and acidifies it...it progresses through the concrete cover, once it hits the rebar, the rebar rusts...rust takes up twice as much volume as steel, and then pops the remaining concrete off in a process of "spalling"...at which point it's often "goodnight nurse" for the structure....realkalisation involves coating the whole structure in paper towels soaked in Potassium Hydroxide, and steel mesh, then passing a current through that, the concrete and rebar to repair the concrete....often cheaper to demolish ad rebuild.
The Colluseum has been standing for thousands of years...don't expect any modern concrete structure to be there that long.
