So does modern concrete.
True, but modern concrete gets pretty close to its maximum hardness in a matter of weeks, and then goes up slowly from there. Roman concrete hardened much more gradually. You wouldn’t have wanted to put a lot of weight on an ancient Roman bridge until years after it was constructed, at least.
I believe you are taking the pith.
From a wikipedia article on one of the Eddystone lighthouses
The Royal Society recommended Smeaton for the task, and he modelled the lighthouse on an oak tree. He rediscovered the use of hydraulic lime, a form of concrete used in Roman times. The technique allowed concrete to set under water, as Smeaton put granite blocks together using dovetail joints and marble dowels.
Construction started in 1756 at a site in Millbay, where Smeaton built a jetty and a workyard in the south-western corner of the harbour to unload and work on stones. Timber rails of 3 ft 6 in (107 cm) gauge were laid for four-wheeled flat trucks, which were used to move masonry around the site. A 10-ton ship named Eddystone Boat was based here, and transported worked stones out to the reef. The ship carried the 2¼-ton foundation stone out in the morning of 12 June 1756.
How old is this myth?
Do you mean the myth about us moderns not knowing how to make concrete like the Roman’s did? Or does that mean I was wrong about how long it took Roman concrete to cure?
“the ancient Romans made the best concrete” myth.
I think these little nuggets of information are passed around (perhaps by mba types originally, but now by youtubers and podcasters), and they have a life of their own outside of concrete manufacturers (who want to sell you something) and by historians (who are probably sick of the whole thing),
If you wanted longevity, rather than almost instant results, that would be a desirable quality. In environmental terms, at least, building once and building to last is preferable to building with inbuilt obsolescence.
Nope. That’s actually how to mark hardened, resists getting hit by an A-380 type buildings. It’s really neat stuff.
Even when fully cured, Roman concrete is at least four times weaker than modern concrete, too, so you need at least four times more of it, which plausibly outweighs the longevity benefit, especially since current progress in zero- and negative-carbon concrete means the environmental impact of replacement in a few decades will have much lower environmental impact than using much more concrete now. Also, I do expect us to move, at least in some cases, towards composite rebar, which will go along way towards reducing the difference in longevity anyway.
Planning for longevity is only an environmental benefit when the thing you’re building is still useful long into the future. Otherwise you either lock your descendents into suboptimal choices for future development to try and repurpose or update around it, or they have to tear it down (in whole or in part) anyway or build a new thing right next to it, wasting much of that extra investment you made. This wasn’t problem before the industrial revolution when tech advances were very slow. But today, you need to account for how different the world will be 50 or 100 years from now.
As a rather extreme example, consider hospital architecture. A hospital built 50, let along 100, years ago would had nowhere near the capabilities needed in a hospital today: power, load bearing for heavy equipment, HVAC, security, distribution of rooms in different departments, health and safety requirements, and so on. If you were charged with updating one, you’d have to just hope it was designed with easy upgrading and modification in mind. Or, you’d be building new wings and buildings and just dealing with the layout not being what you really need.
Longer build times also have a dramatic impact on how you finance projects. When stricter regulations started making nuclear power plants take longer to build, the cost of financing their construction went up very rapidly (anyone backing a project like that knows they could make 8-10% a year investing their money elsewhere with similar or less risk, and will naturally price that in), which is one of the reasons they stopped getting built at all outside of a few governments that back them directly. Whether you think that’s a good thing or not, I’d be very hesitant to do the same to roads and bridges. I wouldn’t want to make Boston’s Big Dig the default, expected level of cost and time overruns.
I did not advocate using Roman concrete – more that considering a development which improved longevity, if necessary at the expense of speed, would be more beneficial than creating structures apparently based on election cycles. If the world is going to reduce carbon dioxide emissions then it will have to change the way it builds (among other things). So designing with upgrading and modification in mind is going to be contributory to that.
Fair enough, I definitely agree with that.
this sort of thing?
Yeah. It’s really really weird, and IANAP(hysist) so I can’t tell if it’s BS or real. But I do know that some effectively blast hardened structures* engineered and built for the US government use different sized chopped up carbon fiber mixed in, treated the concrete with an electromagnetic field after pouring and have a wholly different anti-spalling layer on the inside. You can do really weird things with laid scrims / veils and include not just orthogonal reinforcement but 45° or whatever.
- a bunch of the hardened parts of the 2001 US State department such as the entire Istanbul Consulate were built this way. They still have tons and tons and tons of rebar.
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