Old vs. New: Concrete

Ed pointed out this discussion taking place on another blog regarding the durability of the concrete used in Roman times vs. what we have to work with now.  I thought it was really interesting, considering that folks building a castle with non-traditional methods might choose a concrete reinforced structure as a building option. 

The author's opinion is that reinforcing concrete ruins it, causing splitting and cracking; adding too much water to the mix is bad (Roman concrete was "zero slump"), that ancient structure's longevity is partial proof of this. 

I think he is partially correct.  Yes, steel will rust and expand, causing failure of the concrete.  Without a doubt.  But there are some major differences between then and now in construction philosophy.  I'd be willing to bet that an Roman engineer, presented with re-bar and shown its abilities, would have fired half the workforce used to build those massive structures and put it in his concrete!


So, the Romans used rubble walls with stone or brick cladding.  This allows for a lot of flexing, and essentially makes a composite structure.  Even if the concrete begins to crack, the stone or brick will prevent it from going anywhere.  The structures were also massive, many feet thick.  This also prevents shifting or collapse.  Try building a one foot thick wall using Roman methods, I bet it never makes the 500 year mark, and would probably be lucky to make 100 years. 

Also, let's consider that reinforcing concrete allows us to build structures lighter, thinner, and higher than any Ancient Roman could have.  It also can prevent us from being buried under our structure in event of an earthquake, even if some of the concrete should fail. 

So, while I agree that re-bar is bad for longevity, the alternative is massive structures needing much more time, money and material; and that's from bridges to the slab under your house.

BTW it was nice to see the pics of Rome again, we were just there a couple of months ago and saw a lot of the same places.  We ate at that very pizza roach-coach in the foreground of the Pantheon picture.