On Architecture

What Hacker News says

1. galfarragemNov 2021
   > Are there any foundational texts?

   The treatise on Architecture from Vitruvius, a Roman architect. This is it.

   https://en.wikipedia.org/wiki/De_architectura

   thread
2. af78Jan 2023
   Relevant thread: https://twitter.com/cleptok/status/1611622181665923075

   Ok. Let's do a short thread on Roman cement for the 3 people out there that might be interested. You often hear that the Romans had some sort of superior and arcane knowledge on superior cement mixes that has been now lost. And still today we cannot replicate it. This is complete nonsense. Modern day cement (and any other building material, really) is far, far superior than anything from the past. There is simply no comparison. Above everything we understand the chemical composition, interaction and quality control for consistent results.

   Romans were making mortars based on volcanic ashes. There was no set recipe. Every builder had their own. Volcanic ash from Pozzuoli, crushed brick, slaked like, animal fat, hair etc. Some basic rules existed (as recorded by Vitruvius on the 10 books on Architecture).

   Millions of structures were constructed these way. With the exception of a handful, most of these do not exist anymore. But why the ones that exist are still standing strong?

   Usually via a simple Darwinian process. Most of these times those builders got it wrong. But in a few cases, out of luck, they got the chemistry just right. This would result in a ok-ish material, with decent properties. Not only that. Unreinforced (without steel) concrete will not suffer any serious deterioration, with few exceptions. (Pantheon in Rome) Also the very coarse pozzolan they were using, will chemically react very very slowly producing low initial strengths Vs any modern material.

   In the long term (centuries) though, it will continue gaining strength. Totally useless for the original purpose of the builders, but quite good for the few surviving buildings.

   So what the latest MIT research told us? That lime in very small quantities will be "self-healing'. And this somehow is something that the Romans knew and used to create a superior cement.

   This is simply not true. It is well known that lime expands (the pompous "self-healing" tag), so in very small and precise quantities it will counteract the shrinkage and cracking behaviour of cement binders. But you have to be pretty lucky to get it just right.

   So not intentional. Just survivor bias in the remaining Roman cement structures. Beyond this, lime is a definite no-no for any concrete with steel in it -it corrodes it. The reason we use concrete today is precisely the embedded steel. It allows to build all modern structures.

   And steel is the reason modern concrete deteriorates. It corrodes, expands and cracks the surrounding concrete. An unreinforced concrete (like the ones Romans used) with modern materials and understanding would last forever. But you wouldn't build anything worthwhile.

   Final. Remember. Cement = the glue, the binder that holds everything together, activated by water. Concrete= the actual building material with binder, water, sand and stones. Mortar= only binder, sand and water (maybe small stones)

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