The Harbors of the Sun (Books of the Raksura, book 5) by Martha Wells

[james_davis_nicoll]

The Harbors of the Sun (Books of the Raksura, book 5) by Martha Wells

Comments

[jamoche]

"as lost as the Roman art of making concrete"

Soo.... about 2000 years later someone will work out what the key ingredient was? http://www.pbs.org/wgbh/nova/next/ancient/mystery-of-ultrastrong-roman-concrete-solved/

[eub]

James linked to this one from 2014:
https://archaeologynewsnetwork.blogspot.ca/2014/12/secrets-of-roman-concrete-revealed.html
which likewise says "it's the volcanic ash", but they have different minerals as the important consequences. -- or maybe not so much, strätlingite and aluminum tobermorite are both calcium aluminum silicates

The newer work seems to be specifically about reaction with seawater, the older work about toughness by impeding crack propagation.

[nojay]

The "secret" of Roman concrete is survivor bias and time. The really good concrete has survived 2000 years and that's the material we're fixated on but all the not-so-good concrete is one with the snows of yesteryear, as the Canadians say.

The other factor is time -- as concrete cures it typically gets stronger given a number of environmental factors. Reinforced concrete may not survive if the steel support rusts and swells internally but undisturbed concrete is a work in progress over decades or even centuries.

There are some excellent "modern" examples of really good concrete such as the Nazi submarine pens in France and other military structures which are pretty much invulnerable to demolition today -- breaking the material up using diggers and such doesn't work and enough high explosives to do the job would level the nearby cities.

[armiphlage]

Albania is littered with little mini-bunkers, too small to even be good as a garden shed. People plough and build around them because of their indestructible nature.

Apparently the quality control method was to put the chief engineer inside the prototype and shoot at it with a tank. After a few iterations, they came up with the design.

Of course, this might just be the explanation given to shut up annoying tourists.