Scientists replaced 40 percent of cement with rice husk cinder, limestone crushing waste, and silica sand, giving concrete a rubber-like quality, six to nine times more crack-resistant than regular concrete. It self-seals, replaces cement with plentiful waste products, and should be cheaper to use.

[u/mvea]

https://newatlas.com/materials/rubbery-crack-resistant-cement/

[u/ImFamousOnImgur]

I did a paper in undergrad about Roman concrete. Their recipe was no joke. It’s a big reason why their stuff is still standing to this day.

Coliseum? Yup. Roman concrete. Oh and you know how some of the walls collapsed after an earthquake in 1500 something? Yeah those were the sections that were built by a different architect and he didn’t use the same materials.

[u/noelcowardspeaksout → u/ImFamousOnImgur]

For the Pantheon they used different grades of concrete made with different additives depending on the qualities they required. The dome has pumice included to make it light for example. It has stood for around 2000 years without being rebuilt.

Edit: Pantheon

[u/ImFamousOnImgur → u/noelcowardspeaksout]

Yup. It’s quite amazing the amount of knowledge they had. A lot of that knowledge was lost when the empire fell.

They think the secret to the quality was the volcanic rock used, and if I recall, it was especially good at setting underwater even.

[u/Telvin3d → u/ImFamousOnImgur]

Yes and no. They had an amazing depth of institutional empirical knowledge but that shouldn’t be confused with theoretical knowledge.

So they knew that crushing up rocks from a specific quarry produced a certain result. But extremely limited understanding of why. When people say “the secret of concrete was lost after the Roman Empire fell” its not about a bunch of people suddenly forgetting the recipe. They literally lost track of the particular hole in the ground that concrete came out of.

[u/[deleted] → u/Telvin3d]

Also, a lot of the reason these ancient concrete structures stand for so long is because everything is built in compression. Modern construction uses reinforced concrete, which allows for more efficient building techniques, but the steel reinforcement can rust and decay, causing failure of the member.

[u/jacques_chester → u/[deleted]]

There's also simple survivorship bias.

We only see the remarkable structures that survived. We don't see all the crappy structures that didn't.

[u/[deleted] → u/jacques_chester]

There's also just choice, we're fully capable of building structures that would make roman concrete look like plasterboard but thats expensive and no one wants to pay for a building thats going to outlive their entire nation, nor is anyone going to want to construct a building thats going to last forever because thats bad business.

[u/Ubermidget2 → u/[deleted]]

This logic is crazy to me. Infrastructure may not be cheap, but the benefits of always using the strongest material available would always offset the cost.
We would be able to use less material. Less maintenance would be required, because structures are designed to last longer.

There are also certainly structures we do want to outlive us. The Sydney Harbour Bridge was opened 1932 and will last (hopefully) another 87 years at least.

[u/sebaska → u/Ubermidget2]

This is totally not true, on multiple levels. Strongest material is diamond, but one may argue it's not really available in large enough quantity. Many other strongest materials like composites are not the most durable. And are very expensive.

There's an old adage: Every idiot could build a bridge that stand, but it takes an engineer to build one which barely stands.

[u/[deleted] → u/sebaska]

Personally If I was building a wide squat structure like the colosseum I'd pick ceramics, it'd be expensive as all hell but with giant solid pieces of the right ceramic you could have what would be akin to a building the thing entierly out of solid steel only it'd be entierly rust and corrosion resistant.