They didn't reinforce it with iron.
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Why was Roman concrete so durable?
171–180 of 299 posts
Re: Why was Roman concrete so durable?
#172Isn'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)?
I'm just going to throw it out there to spread the word; GFRP Rebar (Glass Fiber Reinforced Polymer) is a thing, and you can buy it today at your local hardware store. I really wish I would have known about it on my last project, probably the last time I will buy steel rebar to put in concrete. I'm not an ME, but my understanding is that it is a comp in terms of structural reinforcement. I'd be really interested to d…
I recommend Tyler Ley's youtube channel[0] entirely devoted to concrete. He has an episode[1] addressing GFRP that might interest you.
Re: Why was Roman concrete so durable?
#173I think the bigger question for me, and it comes up about half the time when the topic of Roman concrete comes up, is to what extent Roman concrete has a lower or higher lifetime carbon footprint than modern concrete.
Stronger concrete means either less concrete or a slower replacement schedule, and the Roman formula absorbs a certain amount of CO2 out of the air as it ages.
The second to last paragraph of this article talks about it:
> Through the extended functional lifespan and the development of lighter-weight concrete forms, he hopes that these efforts could help reduce the environmental impact of cement production, which currently accounts for about 8 percent of global greenhouse gas emissions. Along with other new formulations, such as concrete that can actually absorb carbon dioxide from the air, another current research focus of the Masic lab, these improvements could help to reduce concrete’s global climate impact.
As we reach the end of the petroleum economy we are going to have a problem with making asphalt, as it is essentially diverting a waste stream from oil refining. When we only use petroleum for materials instead of setting it on fire, that's not going to be a 'free' stream of materials anymore.
Re: Why was Roman concrete so durable?
#174Isn'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)?
I'm just going to throw it out there to spread the word; GFRP Rebar (Glass Fiber Reinforced Polymer) is a thing, and you can buy it today at your local hardware store. I really wish I would have known about it on my last project, probably the last time I will buy steel rebar to put in concrete. I'm not an ME, but my understanding is that it is a comp in terms of structural reinforcement. I'd be really interested to d…
Mike Holmes, a home reno personality in Canada, had been touting its benefits in about the mid-2000s for home foundation re-pours.
Re: Why was Roman concrete so durable?
#175Chemistry 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…
"Chemistry might be important" Conc is nearly all about chemistry. You mention curing rather than drying so you surely have some idea about what is going on. The Romans did not have electron microscopes so could not watch the way the matrix develops around the aggregate etc etc from the get go. To be fair, I fried my first sample in the beam at college by over focussing. They didn't use rebar because they generally b…
> Roman engineers managed to invent an ancient wonder of chemistry and physics that was concrete.
Technically, the ancient Egyptians used concrete in construction long before the Roman engineers were a thing. The difference is they used it for mundane things like wine cellars while the Romans integrated it into their whole architecture system.
Once in a while that art history degree comes in handy…
Re: Why was Roman concrete so durable?
#176Earlier quoted context omitted.
Sounds like a good way to make people slow down.
The problem with making people slow down is that it slows people down.
Sometimes that's what's needed.
Re: Why was Roman concrete so durable?
#177Earlier quoted context omitted.
The rust is essential to bind it to the cement. Without, it adds little strength. Modern concrete isn't expected or designed to last more than a century. It could have been made to last longer, if they wanted, but that would cost a little more. Making no provision for when it will predictably fall apart is a modern failing. That major construction with concrete is about a century old should worry everyone. We have a…
> The rust is essential to bind it to the cement. Without, it adds little strength. Do you have a citation for this? As far as I know this is entirely not true. Rust is an expansionary product - when steel rusts its volume increases something like 10x, which reduces the connection between the concrete and the steel and causes issues like cracking and spalling. Minimizing rust improves the long term performance of reb…
They leave the rebar out to rust a bit, on purpose, before they pour. Surface rust is good, but more is bad. Like many things in life.
Re: Why was Roman concrete so durable?
#178It is a testament to the ingenuity and expertise of the ancient Roman engineers. It will be interesting to see what other insights this research may lead to and how it could potentially be applied to modern construction techniques.
The subject is complicated. For example see this paper[0]. The setting of concrete goes on for a long time and the Romans were probably not aware of how long their concrete(s) was/were going to last. There is a type of 'survivorship bias' going on here. But still, I guess, they knew something important. Adding reinforcement to concrete may well be a source of shortevity - or what ever the complement to longevity is.…
It’s not like the Romans started out in a place where there weren’t thousands of years old structures nearly everywhere they went.
Assuming they didn’t want their structures to last as long as the ancient ones (at their time) is just laughable.
Re: Why was Roman concrete so durable?
#179Isn'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…
Another method is to connect all the rebar and add a https://en.wikipedia.org/wiki/Galvanic_anode
Re: Why was Roman concrete so durable?
#180Earlier quoted context omitted.
this isn't really possible. For the rebar to take up meaningful tensile stresses, the concrete nearby must have cracked. Reinforced concrete ALWAYS cracks. If you want better corrosion resistance, you do other things - lower water ratios, increased concrete cover, sulfate resistant concrete with lower permeability, different reinforcing or epoxy coated reinforcing, etc.
Not always, if rebars are pre-tensioned before concrete solidifies. So the rebar is always under tension. Pretty common in prefab parts, like bridge bars.
pre-stressed concrete is great, and has many advantages over regular reinforced concrete and is more efficient in terms of cross section so cracks less. It still cracks, though, and in different locations like on the ends horizontally instead of at high moment/deflection areas vertically. Pre-stressed does experience fewer shrinkage cracks, which is nice. It's more expensive to build and repair.
And while you absolutely have pretensioned girders on bridges commonly, the bridge decks generally aren't, although they're almost always completely in compression and the steel is there for shrinkage cracks etc.