Some day in the very far future, our descendants will ask, why is the code manually made in the 2020s with Rust so durable, while our modern PHP20457 code that is spit out by Tardpilot100 is so fragile? Our modern operating systems need to reboot 1000 times per hour just to function while ancient operating systems could stay on for months at a time without rebooting!
Why was Roman concrete so durable?
131–140 of 299 posts
Re: Why was Roman concrete so durable?
#132Isn't the particularly short lifespan of modern concrete construction mostly a combination of its use in areas with regular freeze-thaw cycles and using a reinforcement material that rusts (and in doing so expands, damaging more concrete and hastening further water inclusion)?
The rusting and getting wet is cyclical in nature and part of what accelerates that is the formation of cracks in the first place. Part of the maintenance of concrete is to fill any cracks that you can find to prevent it from getting worse. The cracks typically start small, and they might form in places that are hard to get to as well as being too small to see, so if the concrete is self-healing it will prevent some of these small cracks from getting worse on their own which should reduce the effect of expanding water (ice) as well as expanding rust.
The reinforcement material (rebar) already has a very close thermal coefficient of expansion to concrete and this can be thought of as kind of a lucky coincidence.
Re: Why was Roman concrete so durable?
#133> following all of the detailed recipes that had been optimized over the course of many centuries i wonder how all those detailed recipes were passed around for many centuries and now all is gone. Was it all passed down verbally?
Some of it was "stone from this volcano" and then it was mined out. They didn't know how to choose a substitute.
Re: Why was Roman concrete so durable?
#134Isn't the particularly short lifespan of modern concrete construction mostly a combination of its use in areas with regular freeze-thaw cycles and using a reinforcement material that rusts (and in doing so expands, damaging more concrete and hastening further water inclusion)?
The rusting and getting wet is cyclical in nature and part of what accelerates that is the formation of cracks in the first place. Part of the maintenance of concrete is to fill any cracks that you can find to prevent it from getting worse. The cracks typically start small, and they might form in places that are hard to get to as well as being too small to see, so if the concrete is self-healing it will prevent some…
> as well as expanding rust.
Ideally they’d seal before the rebar is exposed and can rust. As long as the rebar is encased, unless you fucked up dramatically it should be safe.
Re: Why was Roman concrete so durable?
#135The research paper: https://www.science.org/doi/10.1126/sciadv.add1602
One method to reduce cement’s carbon footprint (which accounts for up to 8% of total global greenhouse gas emissions), is to improve the longevity of concrete through the incorporation of self-healing functionalities. The resulting extended use life, combined with a reduction in the need for extensive repair, could thus reduce the environmental impact and improve the economic life cycle of modern cementitious constru…
Survivor bias comes up every time this topic is mentioned, but it really has less explanatory power than most people think. If you meet a man born in 1932 who is still running marathons and doesn't need glasses, it's probably luck, although he might have some valuable diet tips to share. If you meet a man born in 1732 running the same marathon, it's time to rule out luck, and start collecting blood samples because he might actually be some kind of vampire.
Furthermore, the "survivor bias" idea, as an attempt to explain the longevity of Roman concrete as a building material, implies that the buildings that survived were stronger than the ones that did not, so we're just seeing the upper end of structural strength. But that's not even necessarily the case. Many more were lost because they were deliberately demolished for other reasons (honoring the wrong gods, etc). And it's not like these buildings only survived in ideal environments for preservation; as the article mentions, they have survived in many different climates across a vast empire, standing in seawater, through earthquakes, and so on.
Re: Why was Roman concrete so durable?
#136Earlier quoted context omitted.
Then multiple that by 20 (the lifetime of the road surface) and factor in that the resurfacing is significantly cheaper than the initial build and you quickly find roads are easily subsidized by property taxes.
There are two sides to this coin. The roads need repair continually and resurfacing eventually, yes. What happens when property values and the local economy begin to deteriorate instead of prosper? All those utilities and public rights of way still need those repairs, but there's no appetite to raise property taxes, and the tax base is dwindling, and there's little reason to keep paying the mortgage on a depreciating…
NotJustBikes covered this too:
https://www.youtube.com/watch?v=7IsMeKl-Sv0
Re: Why was Roman concrete so durable?
#137Isn't the particularly short lifespan of modern concrete construction mostly a combination of its use in areas with regular freeze-thaw cycles and using a reinforcement material that rusts (and in doing so expands, damaging more concrete and hastening further water inclusion)?
And being driven over by semi trucks full of heavy cargo 24/7.
Re: Why was Roman concrete so durable?
#138Chemistry might be important, but we don't necessarily need that deep of an analysis. Romans didn't mind over-engineering with massive, inefficient structures. They didn't worry about complex/thin shapes, or any tensile elements. No rebar, no "piping" cement, etc. And they could put up with extremely long cure times. The end result is very, very dense concrete. We could probably recreate the durability of their concr…
Yeah, I can't imagine a municipality letting their concrete roads cure for a couple years before letting cars on them.
Re: Why was Roman concrete so durable?
#139on the other end of the spectrum, did you know concrete can be used to demolish concrete? dexpan is a special demolition concrete mix that, when poured into holes, expands at 18kpsi. it gets used when jackhammers and explosives cant be used, for example, in refineries and explosive atmospheres.
It's also useful if you want to do concrete demolition yourself using only hand tools. You drill holes, pour, wait for cracks, and then use a pick and hammer to remove the remaining chunks. Often sold as "expansive grout".
If you can drill holes you can use stone splitting wedges.
A lot of these high dollar modern miracles of chemical engineering are purely for use in situations where it's cheaper to just buy the $100/tube stuff than it is to try and get the approval to do something sensible. Basically you're paying to get around process tech debt.
Re: Why was Roman concrete so durable?
#140Earlier quoted context omitted.
Interestingly, the article founds out that their concrete cured quickly. Anyway, no, our usual concrete completely breaks down in a few centuries. No matter how it's structured, it does not match the durability of that concrete without ongoing maintenance.
>> A few centuries Sounds good to me? Although, many centuries old sound structures also sounds better to me...
Like the Pantheon[1]? It's still got the world's largest unreinforced concrete dome and it's in active use as a church not to mention major tourist attraction.