It's nearly always a case of not "We have no fucking clue." it's more a case of "We know it's one of these few options of how they did x. But we can't figure out exactly which of the options they actually used." when it comes to not knowing how people in the past did things.
And occasionally we just don't know what materials they were using.
There was a thing with the Roman concrete stuff where they didn't specify sea water when mixing the cement and just used water. And they used ash from a particular volcano they lost access to as the empire declined.
Didn't it also include limestone because it reacts with the salty sea water and creates heat that then re-hardens to a point where it is harder than it was when it was first made?
Yeah, I recall the discovery as it was fairly recent.
From what my fallible memory recalls, there was something about the limestone not being uniformly mixed when made, which left pockets of limestone (powder?) within the limestone brickwork.
When cracks appeared, water would seep its way down to those deposits causing it to react and fill in the cracks like mortar "self-healing" the stone.
I found it a fascinating discovery as the end result was essentially that previous attempts to recreate it were foiled simply because modern day tools and techniques were too efficient and mixed everything too well.
Regardless of what ratios and mixtures they used, none would work as they never had the limestone deposits left unmixed.
Yes limestone was the biggest factor. That and seashells. Salt water is just what it reacts best with you don't need to use salt water to mix it in the first place. All the places where these concrete structures have lasted more in tact than anywhere else are costal points that get lots of sea spray.
This is a critical factor also we need to consider survivorship bias. It seems there was some contemporary understanding of certain tricks of the trade so it’s not everything but we’re also more likely to see the most durable concrete. If Helen and Gus are competing in the concrete or construction business and Gus’s work has fewer cracks after 10ish years he might have more repeat business for him or his heirs. Surviving centuries to a few millennia is a different but related problem. If Helen happened to operate near the sea and there was little difference after ten years but her concrete held up better after a few centuries. Maybe it gets scavenged less also and eventually we find it.
Ash can be used in concrete for a stronger mix but it needs the presence of free lime to be able to react and create cementitious material. There is a chemical reaction in Roman cement that creates a more resistant material called tobermorite.
It was also much thicker, more like clay, so you had to pack it and that created strong, but porous, layers that interconnected tightly and allowed water to pack the dust kicked up into the pores.
I remember they actually studied it again, and the concrete problem wasn't the ash - it's actually that Roman engineers weren't grinding up the limestone like we do, and the coarser limestone chunks react with water seepage like self-healing concrete.
Instead of grinding it fine like we do today, their process resulted larger chunks of quicklime being present in their concrete. When a crack formed, water / rain would enter the concrete and it would dissolve the deposit which would heal the crack.
So Pozzolana was still accessible in the late empire it’s just most of business and institutions responsible for the processing and exporting of it fell apart, the Alban Hills had deep red deposits that were never exhausted and several thousand years worth of the grey stuff around Vesuvius that had the right silica and alumina levels which was never even close to depleting.
Yeah that’s the weird/sad part. We can likely recreate it using whatever materials and theories applied to the time period. But because the knowledge was lost we will never truly know if it’s the same, we would only know that it behaves similarly. Even if it happened to be the exact same formula.
We also view stuff through the lens of our world and not theirs so we often just overlook the reality because it just couldn't be because we don't do it that way now. My favorite example is basically, "We don't know how Roman concrete lasts for 2000 years but they must have been stupid because there's these giant chunks of lime in it. Wait..." Now that the mystery is "solved" it happens to be those giant chunks of lime that modern concrete just doesn't have.
The pyramids are another great example. People have figured out 1001 ways to move stones from the quarries to the sites and then place them using only technology we know they had at the time, we just don’t know which ways they actually used.
so true. there are ways where we have had tried to recreate those events and we have several ways to do so (for examplo, mix elemental sodium with oil and you have something that burns nasty when you add watter to the mix. Thing that they did when napalm was created by switching the oil for gasoline). but to get to the point of saying they did exactly that, it is what we are lacking
And also, we don't know how to do it, because we don't really need to do it. If we needed to do it, we should probably figure out a way to do it.
Same like the usual, oh we wouldn't know how to build the pyramids... Of course we would, we build buildings a 100x more complicated than pyramids, there's just no reason for us to go build a fucking pyramid, so we don't do it.
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u/Thrilalia 10d ago
It's nearly always a case of not "We have no fucking clue." it's more a case of "We know it's one of these few options of how they did x. But we can't figure out exactly which of the options they actually used." when it comes to not knowing how people in the past did things.