https://www.sciencealert.com/we-finally-know-why-ancient-roman-concrete-stood-the-test-of-time

sample quote

One of the questions in mind was the nature of the lime used. The standard understanding of pozzolanic concrete is that it uses slaked lime. First, limestone is heated at high temperatures to produce a highly reactive caustic powder called quicklime, or calcium oxide.

Mixing quicklime with water produces slaked lime, or calcium hydroxide: a slightly less reactive, less caustic paste. According to theory, it was this slaked lime that ancient Romans mixed with the pozzolana.

Based on the team's analysis, the lime clasts in their samples are not consistent with this method. Rather, Roman concrete was probably made by mixing the quicklime directly with the pozzolana and water at extremely high temperatures, by itself or in addition to slaked lime, a process the team calls "hot mixing" that results in the lime clasts.

"The benefits of hot mixing are twofold," Masic said.

"First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction."

And it has another benefit: The lime clasts give the concrete remarkable self-healing abilities.

When cracks form in the concrete, they preferentially travel to the lime clasts, which have a higher surface area than other particles in the matrix. When water gets into the crack, it reacts with the lime to form a solution rich in calcium that dries and hardens as calcium carbonate, gluing the crack back together and preventing it from spreading further.

end quote

It's always impressed me how Greek & Roman ruins are still standing, when a lot of structures from the last 50 years or so aren't.

Here is an old (90's) Nova episode that is a fun watch. They talk about Roman concrete.

https://www.youtube.com/watch?v=GL5bBs4bPrE&ab_channel=AbsolutelyAnything

What procedure did they use to get it hot since all they had was a fire and a pot? Was it made in 5 gallon batches?

Freeze/thaw cycles are hard on concrete and brick mortar. Perhaps the more stable Mediterranean climate where these structures were built has something to do with why they have lasted so long as well?

Both good reads.

Same, or similar, to how they made ceramics. You know, pots and such?

In a kiln

Those old structures also don't use steel reinforcement either. Our bridges and highway overpasses fail from the inside out due to rebar corrosion beneath the surface. They did a lot with what they had available to them regardless.

I did a coupe pre rev war home restorations which involved mixing lime with the plaster and horse hair. Not the most fun.

I'm going to have to read/watch these. Sounds super interesting.

Interesting how the European societies went to he11 after roman faded.

No organization with brain dead leaders and drug sons.

A 50 to 150 year span of bad weather may have had a strong hand in causing Rome to decline.

https://www.livescience.com/attila-the-hun-raided-to-escape-drought

https://www.science.org/content/article/why-536-was-worst-year-be-alive

Hiring foreign mercenaries rather than rigorously training citizen soldiers didn’t help either.

Another learning example IMO of a flaw in the Proverbial "Common sense" mantra ie "everyone knows concrete must be mixed real well"? thinking?

Look at the Atlantic Wall from WWII. It's falling apart from exactly what you stated. Water, freezing, and corrosion.

That is not a great example in this context IMO. The Atlantic Wall was never intended to last more than a decade I suspect. AH frowned on the use of concrete for his most important structures, he wanted those to last a thousand years, which concrete at that time would hardly last 100 years, but stone was up to the task, irrespective of rebar failing/corrosion/expansion. This nation has a number of TVA dams built prewar in a hurry that are way past their design life for concrete and must be dealt with soon. Personally, I am most impressed with the imported concrete used in the Florida Keys bridge system to Key West, that has withstood countless hurricanes, extreme temps, constant saltwater exposure and decades of traffic, and is still standing with zero Maintenace for over forty after being built over 110 years ago privately.

old piers originally poured in year 1911

old photo

Nice pics btw, but those pics are of a maintained section of bridge to Pigeon Key still used today for limited traffic, there are countless miles of other concrete bridges in the Keys also still erect and maybe still useful if they had the steel structures maintained.

BUT just like all products made today, I you build it to last they will be out of the perpetual work. Ah, Dentist, lawyers, Doctors, tire companies, most anything that wants their doors stay open.

Touche!

Alternative cement made from slag leftover from steelmaking plus salty brine left over from ocean water desalanation.
One funder is former NBA player Rick Fox.

https://www.partanna.com/technology

https://meconstructionnews.com/5607...tive-the-key-to-carbon-negative-projects