Secret to durable ancient Roman concrete revealed

[Szdfan]

As it's been often pointed out, Paul was not afraid to use his Roman citizenship to his advantage and early Christianity used the Roman-built road system to help spread the faith.

[MaxPC]

As it's been often pointed out, Paul was not afraid to use his Roman citizenship to his advantage and early Christianity used the Roman-built road system to help spread the faith.

Early Christians used the opportunities at hand: they were quite versatile and resilient. If Paul had been a citizen of Tanzania or India, most certainly he would have used that advantage to spread the Gospel. There were quite a few byways that were not Roman roads, particularly in the areas north of the empire, yet Christianity found its way there. The Apostle Thomas took the Gospel to India without Roman roads.

I do not think Rome and its tech was essential to the spread of the Gospel. It merely provided a convenience in certain areas. As we have seen in our respective histories, convenience was not a requirement for the spread of the Good News.

[Heirbyadoption]

God saw fit to destroy the Roman civilisation and cultivate Christianity as its replacement. I’d say we got a very good exchange, all things considered.

But of course that isn't really what happened.
The western half of the Roman Empire descended into anarchy and the dark ages long after it had become Christian. The collapse of the western empire is usually dated to about 175 years after Constantine.
The eastern half of the Roman Empire lived for another 1000 or so years as the Byzantine Empire until it was destroyed and absorbed by the Ottoman Turks.

Ken: The direction of the dialog here is in the relevancy of destruction vs transformation. It would be good if you were to keep to that direction instead of lecturing others on that which you view as fact.

I'm confused, I guess... Was what Ken shared not actually historical fact, as opposed to Josh's generalization that "Christianity" replaced "Roman civilization" (by implication, with the fall of said Roman empire)...?

[MaxPC]

Ken: The direction of the dialog here is in the relevancy of destruction vs transformation. It would be good if you were to keep to that direction instead of lecturing others on that which you view as fact.

I'm confused, I guess... Was what Ken shared not actually historical fact, as opposed to Josh's generalization that "Christianity" replaced "Roman civilization" (by implication, with the fall of said Roman empire)...?
[/quote]

If it were to be examined closely, it was incomplete fact and one that was meant to derail Josh's points. Such behaviors that target an individual to embarrass him is unacceptable. Case in point from the "Interesting Times" thread:

… so spending $41 billion less on the IRS adds to the deficit?

How about letting hard-working Americans just keep the money they earn from their yard sales, instead of hiring IRS agents to go harass them?

I know Josh. Math is hard. Do try to keep up.

The important point here is that Josh and I were having a discussion regarding God and the destruction of worldly kingdoms. Interruptions of that exchange for selfish reasons is not acceptable.

[ohio jones]

Back to the actual subject line ...

It's aliens, isn't it?

Actually it's the absence of steel reinforcement.

https://constructionphysics.substack.co ... n-concrete

The comparatively short lifespan of modern concrete is overwhelmingly the result of corrosion-induced failure. Unchecked, reinforced concrete exposed to the elements will often start to decay in a few decades or even less.

If we have the possibility of building more durable concrete buildings, why don't we?

This doesn't seem that complicated to me. Using unreinforced concrete dramatically limits the sort of construction you can do - even if the code allows it, you’re basically limited to only using concrete in compression. Without reinforcing, modern concrete buildings and bridges would be largely impossible.

[MaxPC]

Actually it's the absence of steel reinforcement.

https://constructionphysics.substack.co ... n-concrete

The comparatively short lifespan of modern concrete is overwhelmingly the result of corrosion-induced failure. Unchecked, reinforced concrete exposed to the elements will often start to decay in a few decades or even less.

I seem to recall there is a glaring example of such a failure. A bridge crossing Tampa Bay in Florida was found to have this type of corrosion. I have to wonder if our reach has exceeded our grasp (or ability to safely build) when considering new designs.

[RZehr]

From the article:

Previously it had been noticed that Roman concrete often had calcite filled (CaCO3) cracks in it. The researchers suspected that the lime clasts might act as a sort of self-healing mechanism for the concrete - water making its way through the concrete would pull along calcium ions from the lime clasts, which would then form calcite, sealing the cracks.

To test this, the researchers first made their own mixes of concrete which included various amounts of quicklime, resulting in a concrete with lime clasts. They then split apart test samples of the concrete, put them back together with a 0.5mm crack in them, and ran water through the samples. Over a period of 1-3 weeks, the cracks filled with calcite and healed. Cracks in conventional concrete samples, on the other hand, didn’t heal, and water continued to run through them.

And:

One other key point is that self-healing isn’t a unique property of Roman concrete. Modern concrete will also self-heal small cracks, though it appears to do so with a different mechanism than lime clasts. The (apparently) notable thing about the Roman self-healing is the size of the cracks that it can heal - modern concrete can heal cracks up to 0.2-0.3mm, whereas the lime-clast mix could heal cracks up to 0.5mm. It’s possible that the ability to heal larger cracks will significantly extend the lifespan of concrete, but it just might not matter that much. After all, the self-healing ability of normal concrete doesn’t prevent it from failing.

And even if it does extend the lifespan of concrete, it’s not obvious how much a difference that would make in practice. As we’ve seen, we already have ways to make concrete last longer (including with coatings that can seal cracks up to 0.5mm), and it’s very unclear whether this would be a meaningful addition to that palette.

[RZehr]

Then this https://www.foxnews.com/science/researc ... urable.amp article says this about temperature:

But a report released Friday discovered that it is not necessarily the ingredients that attributed to the strength of the Roman’s concrete but the mixing process. Scientists in a MIT, Harvard University study found that Romans actually relied on a process called "hot mixing" to whip up their hyper durable concrete.
Scientists in a MIT, Harvard University study found that Romans actually relied on a process called "hot mixing" to whip up their hyper durable concrete.
"The benefits of hot mixing are twofold," MIT professor of civil and environmental engineering Admir Masic told MIT News. "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," he added.

Masic was first alerted to the concept after noticing millimeter-small bright white minerals in the ancient concrete.

The outlet said these deposits, described as "lime clasts" and not found in concrete today, were once chalked up to poor mixing practices.

But the MIT professor took issue with this line of thought.

"The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me," Masic told the publication. "If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product?"
Masic and his team discovered that the white specs were actually calcium carbonate that had been formed after the mixture, which include quicklime, reached an "extreme temperature."

His team then ran a series of tests using modern and ancient techniques with and without quicklime.

The team are now working to commercialize the ancient practices for modern use.

[RZehr]

Practical Engineering has this to say:

But lack of steel reinforcement isn’t the potential only reason Roman concrete structures have lasted for so long. One of the other commonly-cited suggestions for the supremacy of Roman concrete is its chemistry. Maybe they just had a better recipe for their concrete that somehow got lost over time, and now those of us in the modern era are fated to live with substandard infrastructure. In fact, in 2017, scientists found that indeed the combination of seawater and volcanic ash used in ancient roman concrete structures can create extremely durable minerals that aren’t normally found in modern concrete. But that’s not to say that we can’t make resilient concrete in this modern age. In fact, the science of concrete recipes, also known as mix design, has advanced to levels a Roman engineer could only dream of.

One of most basic, but also most important factors in concrete’s chemistry is the ratio of water to cement. I did an experiment in a previous video that showed how concrete’s strength goes down as you add more water. Extra water dilutes the cement paste in the mix and weakens the concrete as it cures. The Romans knew about the importance of this water to cement ratio. In historical manuscripts, Roman architects described their process of mixing concrete to have as little water as possible, then pounding it into place using special tamping tools. Interestingly enough, we have a modern process that closely mimics that of the ancient Romans. Roller Compacted Concrete uses similar ingredients to conventional concrete, but with much less water, creating a very dry mix. Rather than flowing into place like a liquid, RCC is handled using earth moving equipment, then compacted into place using vibratory rollers like pavement. RCC mixes also usually include ash, another similarity to Roman concrete. It’s a very common construction material for large gravity and arch dams because of its high strength and low cost. Again, these are usually unreinforced structures that rely on their weight and geometry for strength.

The miracle of modern chemistry has given us a wide variety of admixtures like superplasticizers to improve the characteristics of concrete beyond a Roman engineer’s wildest dreams. So why does it seem that our concrete doesn’t last nearly as long as it should. It’s a complicated question, but one answer is economics. There’s a famous quote that says “Anyone can design a bridge that stands. It takes an engineer to build one that barely stands.” Just like the sculptors job is to chip away all the parts of the marble that don’t look like the subject, a structural engineer’s job is to take away all the extraneous parts of a structure that aren’t necessary to meet the design requirements. And, lifespan is just one of the many criteria engineers must consider when designing concrete structures. Most infrastructure is paid for by taxes, and the cost of building to Roman standards is rarely impossible, but often beyond what the public would consider reasonable. But, as we discussed, the technology of concrete continues to advance.

https://practical.engineering/blog/2019 ... ete-better

[barnhart]

Maybe this is obvious, but Roman concrete was employed only in compression, never (as far as I know) in tension. The use of concrete in tension generally (always?) required reinforcement, usually steel, which is the failure point.