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Why Roman concrete is still stronger than RAAC (and other modern concretes)
(www.chemistryworld.com)
this post was submitted on 11 Sep 2023
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Is it that we don't know how to make concrete of equal/greater resilience? Or that modern concrete optimizes for something else (I'm guessing cost)? I didn't RTFA.
They are comparing roman concrete to portland cement, the most common formula. The kind of strength being emphasized is durability, because roman concrete has unique chemistry that allows small cracks to fill themselves. Modern special-purpose concrete blends can outperform roman concrete in other measures of strength, however.
Thats right. I remember the engineering dept. of my university would hold "concrete boat" competitions to highlight this point exactly. Concrete is a mixture, and different mistures are used for different purposes. Im not a civil engineer, but I wonder how well would roman concrete perform in 100+ floor buildings or expansive multi-floor complexes. Even if it performs "well", is it cost effective? I doubt it will be better than a min-maxed mix determined by project/area/budget/etc
That's interesting!
Cool! Thanks!
The article suggests that the roman concrete gets it's properties due to using a certain kind of volcanic ash found around Naples, but not common everywhere else, so using their recipe wouldn't be sustainable with the amount of concrete we use these days.
On the other hand, these days it wouldn't be about that specific ash. You could take a look at it, say "oh, yeah, that's just florgium whateverthefuxide" and then there'd probably be readily available sources of it.
Got it.
I have heard too there are differences in available raw materials. Even our newer concrete is not as good as older.
Notice also they said common cement too. I suspect supply and demand meaning cost and obsolecense are what we design for. For that matter too cheap patio blocks are not as good as expensive ones. Sad but we do not build for even decades let alone centuries.
Keep in mind too that technology does not automatically improve. For tech to even continue at the same level we have to continually practice it.
Our newer concrete is better for the goals we are setting in construction, which does not tend to include permanence. Our goals are mostly about strength to weight ratios and other properties that allow for massive numbers of floors with and as little mass as possible with reliability measured in decades. Basically guaranteed to last reliably with minimal upkeep.
We are continuously practicing new ways to build with concrete, wtf are you talking about?
We mostly know how they made theirs, and could make our own version of it, but we optimize for different things.
The Romans optimized for "that's cement and it works well", because they didn't have anything close to the level of chemical understanding we do now.
We optimize for strength and predictability. Ours can hold a higher load and will likely need repairing about when we predict.
Roman concrete can sometimes, in certain circumstances and with variable effectiveness, repair certain types of damage by chemically interacting with the environment. So maybe it crumbles in a decade or maybe it lasts a millennium.
Article basically points at some researchers who are looking to see if they can bring that healing capability to modern concrete in a predictable and more versatile fashion.
It's basically the self healing properties of Roman concrete that I find fascinating.
Oh, it's definitely interesting.
I think people here just got rubbed the wrong way because these articles often make it seem like Roman concrete is better than ours, rather than "look what they accidentally did occasionally".
We can make self healing concrete today, we just usually opt not to, because the downsides or unpredictable nature makes it unsuitable for the significant cost increase.
The phrase "the bridge is infested with bacterial spore colonies" isn't one that makes engineers happy.
Yeah, I think people got rubbed the wrong way only from the title. I don't think they bothered to read it. I don't think the article in any way emphasised that Roman concrete is better than modern; rather it talked about findings of certain researchers. It was the chemistry which I found interesting.
Agreed. The article doesn't really make Roman concrete sound great, it even mentions how limited in availability the volcanic ash they used was.
If we wanted to build to last longer, I imagine not using iron-based reinforcement would get us most of the way there, especially where ice isn't a concern.
Cool! Thanks for the info.