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Why was Roman concrete so durable?

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Re: Why was Roman concrete so durable?

#201

Post by bpbp-mango »

stephencanon wrote: post #197
raspberry1337 wrote: post #191

Earlier quoted context omitted.

It's a nice thought that all these depressive brutalistic/modernist builduings will all soon crumbly by the same mechanism that spawned them!

Most brutalist buildings are already 60+ ish years old and doing great (actual brutalism, rather than “concrete buildings I don’t like,” was mostly a style of the 1950s and 60s in the west, though it lasted quite a bit longer in Eastern Europe). Even the Boston government services center, everyone’s most hated brutalist building in the US is already past 50.

for many people, myself included, actual brutalism is "concrete buildings I don’t like"

Re: Why was Roman concrete so durable?

#202

Post by adgjlsfhk1 »

chrisdhoover wrote: post #187
moloch-hai wrote: post #144

Earlier quoted context omitted.

The rust is essential to bind it to the cement. Without, it adds little strength. Modern concrete isn't expected or designed to last more than a century. It could have been made to last longer, if they wanted, but that would cost a little more. Making no provision for when it will predictably fall apart is a modern failing. That major construction with concrete is about a century old should worry everyone. We have a…

So the Hoover dam will fail in 10 years?

Concrete lasts a really long time when it's under pure compression. You only run into issues when you try to build structures that need to survive in tension. That's when you start having to add rebar and lower weight and you run into issues.

Re: Why was Roman concrete so durable?

#203

Post by moloch-hai »

zoklet-enjoyer wrote: post #186
moloch-hai wrote: post #177

Earlier quoted context omitted.

They leave the rebar out to rust a bit, on purpose, before they pour. Surface rust is good, but more is bad. Like many things in life.

I read your comment as I finished eating my third slice of pie and wondering why I cut myself 3 slices.

You could have cut one big slice instead.

Re: Why was Roman concrete so durable?

#204

Post by adgjlsfhk1 »

ricardobeat wrote: post #196
dreen wrote: post #181

Earlier quoted context omitted.

I was referring to the knowledge of how to make long lasting concrete, not necessarily specifically how the Romans did it, but I guess I could've been clearer.

The answer is still no, we don't know how to make long lasting concrete with modern techniques either apparently. Hence the research. Especially steel-reinforced concrete, the lifespan is only 50-100 years. The only exceptions are massive structures like dams that will probably last a couple millennia.

Right but the thing is neither did the Romans. The only reason roman concrete lasted so long is it didn't use steel reinforcement. All of the structures we have from them are carefully designed to only use compression.

Re: Why was Roman concrete so durable?

#205

Post by moloch-hai »

jcampbell1 wrote: post #198
moloch-hai wrote: post #144

Earlier quoted context omitted.

The rust is essential to bind it to the cement. Without, it adds little strength. Modern concrete isn't expected or designed to last more than a century. It could have been made to last longer, if they wanted, but that would cost a little more. Making no provision for when it will predictably fall apart is a modern failing. That major construction with concrete is about a century old should worry everyone. We have a…

> The rust is essential to bind it to the cement What? This is total nonsense. > Modern concrete isn't expected or designed to last more than a century. It could have been made to last longer, if they wanted, but that would cost a little more. Is hacker news a conspiracy theory website now? > We have a very great deal of infrastructure that will fail on a predictable schedule Wood rots in a few years under certain co…

It is a conspiracy theory that engineering construction is optimized for cost against requirements? Maybe ask literally any civil engineer how much cost matters.

Re: Why was Roman concrete so durable?

#206

Post by hprotagonist »

moloch-hai wrote: post #146
mitthrowaway2 wrote: post #135

Earlier quoted context omitted.

Survivor bias comes up every time this topic is mentioned, but it really has less explanatory power than most people think. If you meet a man born in 1932 who is still running marathons and doesn't need glasses, it's probably luck, although he might have some valuable diet tips to share. If you meet a man born in 1732 running the same marathon, it's time to rule out luck, and start collecting blood samples because he…

Right. Romans experimented with the formula for concrete for centuries, and learned a lot about how centuries-old concrete structures deteriorated. They didn't have modern chemistry, but they had observational skills and were serious about their work. It would not be surprising to find that most structures weren't built to last any longer than ours, but that some were meant for the ages. An important difference today…

The cathedral of st. john the divine in new york city has yet to be completed.

we just don't build a lot of them.

Re: Why was Roman concrete so durable?

#207

Post by IgorPartola »

LegitShady wrote: post #157
moloch-hai wrote: post #144

Earlier quoted context omitted.

The rust is essential to bind it to the cement. Without, it adds little strength. Modern concrete isn't expected or designed to last more than a century. It could have been made to last longer, if they wanted, but that would cost a little more. Making no provision for when it will predictably fall apart is a modern failing. That major construction with concrete is about a century old should worry everyone. We have a…

> The rust is essential to bind it to the cement. Without, it adds little strength. Do you have a citation for this? As far as I know this is entirely not true. Rust is an expansionary product - when steel rusts its volume increases something like 10x, which reduces the connection between the concrete and the steel and causes issues like cracking and spalling. Minimizing rust improves the long term performance of reb…

Rust is perfect. We don’t criticize rust on HN.

Re: Why was Roman concrete so durable?

#208

Post by russellbeattie »

dang wrote: post #54

Related: Why Ancient Roman Concrete Outlasts Our Own (2017) - https://news.ycombinator.com/item?id=29366911 - Nov 2021 (67 comments) 2,050-year-old Roman tomb offers insights on ancient concrete resilience - https://news.ycombinator.com/item?id=28833525 - Oct 2021 (101 comments) Why Roman concrete is stronger than it ever was, while modern concrete decays - https://news.ycombinator.com/item?id=25690803 - Jan 2021 (7…

I was thinking as I read this, "Wait, don't we already know this?" Now I know why.

Re: Why was Roman concrete so durable?

#209

Post by BirAdam »

TheMagicHorsey wrote: post #131

Some day in the very far future, our descendants will ask, why is the code manually made in the 2020s with Rust so durable, while our modern PHP20457 code that is spit out by Tardpilot100 is so fragile? Our modern operating systems need to reboot 1000 times per hour just to function while ancient operating systems could stay on for months at a time without rebooting!

Nah. Rust evangelists of the future will still be fervently rewriting everything in Rust, and they’ll be researching why ancient code worked without being written in Rust.

Re: Why was Roman concrete so durable?

#210

Post by ComputerGuru »

ggm wrote: post #86
ogogmad wrote: post #81

For people who don't know the difference between cement, mortar and concrete: Cement is a substance used for producing mortar and concrete. It's never used on its own. It is a "binding agent". Note that the term "cement" is often not used correctly in everyday speech, with people talking about gluing bricks together with cement, when bricks are actually glued together with mortar. Mortar is the glue between bricks. Y…

Reinforced concrete in part is designed to provide structural strength under tension forces. Concrete is stable in compression but has weak resistance to tension. Pretensioned reinforced concrete permits longer unsupported spans but even vertical concrete can benefit from reinforced bars, to prevent spalling. (I believe). Not all reinforcing steel has to be tensioned to be useful, that's a technique for long spans. R…

> but even vertical concrete can benefit from reinforced bars, to prevent spalling. (I believe).

I liked your comment but this bears correcting. (Corrosion of) rebar is actually the biggest cause of spalling in vertical concrete structures.

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