Comments by "EebstertheGreat" (@EebstertheGreat) on "Getting Buried In Concrete To Explain How It Works" video.

  1. An important fact about Roman concrete is that it was mixed extremely dry. Laborers would pound it into place rather than pouring it, which was only practical because they had a lot of cheap labor and all the concrete was unreinforced. Concrete today is reinforced, which means you need a soupier mix to be able to pour it around the steel reinforcement. Dryer concrete is always stronger (and more labor-intensive). That said, some unreinforced concrete today is still mixed pretty hard, like dams and reservoirs. These are usually made from massive amounts of roller-compacted concrete with no reinforcement, making them extremely durable. Vibratory rollers replace the old pounding and tamping tools. Most other unreinforced concrete today is probably not as strong as that used to make the Parthenon, such as curbs and sidewalks. (Curbs are relatively rich, but they still have to be liquid enough to flow through tubes in the trucks that lay them.) A further thing to consider is that ancient engineers had primitive mathematics and did not know what was required to make a lasting structure. The most important structures were extremely overengineered, using perhaps three times as much material as was actually necessary. This wasted a tremendous amount of money, but because they had no formal science, it was the only way ancient architects could be completely sure their buildings wouldn't collapse (and even then, they weren't always successful). That does mean the ruins of the most overengineered buildings will tend to last a very long time.
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