Knowledge of "Roman cement" roughly speaking was never really lost.
How do you think the quay walls in medieval Dutch and Flemish harbours were built? The mortar was made with Trass [0], a natural puzzolanic from the Eifel, transported along the Rhine.
"Roman cement", also known as hydraulic lime [1] mortar, was in widespread active mainstream use in many places in Europe until the 1920's, and in some the 1930's. In Latvia for example, large scale Roman cement production only came to an end with the second world war flooding specific quarries.
The main problem with these hydraulic cements is they cure/set much more slowly. That's very much guaranteed to limit their use in speed focused modern construction.
There's still a market for hydraulic lime mortars. There's even a euro norm for it, EN-459. These products have excellent breathability and moisture resistance properties. The entire field is seeing a revival in monument restauration and ecological construction. Most straw bale construction in Europe for example is plastered using hydraulic lime plasters.
Some interesting products:
- natural hydraulic limes (NHL), like Saint-Astier from France
- formulated/artifical hydraulic limes (HL), often using blast furnace fly ash
- natural puzzolanic additives, like trass from the volcanic Eifel, has been used continuously since the Roman era!
I think it's worth pointing out that whilst hydraulic limes have good breathability compared to cement, they are still inferior to "air" lime based mortars (e.g. hot mixed or made with lime putty).
Although these have a slower set than hydraulic limes they are still in widespread use and a lot of straw bale construction will be using air lime as a superior alternative to hydraulic lime.
In what way are they inferior? There are a lot of properties of building materials, and correct selection is about the compromise based on what each has. Cure time is one consideration, cured strength is another, R value, mass/volume ratio - and those are what I as a lay person can come up with: I suspect someone with more knowledge as a longer list.
I guess the parent commenter meant to say hydraulic limes are inferior in terms of breathability compared to hydrated lime. Which is entirely correct.
As always, it's a trade-off. Anecdotally, we did the base plaster layer on our straw bale house using hydrated lime for better breathability. We'll probably make the top coat slightly hydraulic using trass.
I've been looking into straw bale construction just out of curiosity recently, do you have some good resources to learn more about construction and regulation?
One book I like is "Building with straw bales" [0], by Barbara Jones. It's mostly very practical. Reassuring also when it comes to using a less usual building technique. A tad bit to the eco hippie side for my taste, but only in minor details. All the important bits are very much grounded in sound practice.
If you want to gather practical experience, come help me fiddle with our straw bale house next spring or summer :-)
Regulation is going to be particular to your municipal or county government. Unless you’re in a major city, the permits desk will probably be approachable and will take the time to explain what you can and can’t do. They will probably entertain a variance unless you seem like you’re really out of your depth. They may be able to tell you about other bale construction in your area.
The primary tldw; is the fact modern concrete uses steel rebar for tensile strength, whereas the Romans relied on architectural techniques to minimize tensile forces on their structures.
Steel rebar is the primary route through which concrete deteriorates.
Architectural design isn’t everything, it appears that their concrete “recipe” was in fact different:
“University of Utah geologist Marie Jackson… and her colleagues have found that seawater filtering through the concrete leads to the growth of interlocking minerals that lend the concrete added cohesion.” http://unews.utah.edu/roman-concrete/
I did a quick check, and it looks like rebar concrete has a lifespan of about 50 years, and I had to check the lifespan of post-tensioned concrete because I suspected it has a shorter lifespan. Most sources are saying 15-20 years for post-tensioned. Any structural engineers able to report in? If that is the case, it's a bit surprising, given how expensive buildings are, although technically I believe post-tensioning can be replaced, but I also imagine that replacement cost would also be high.
Edit: Thanks, civeng, this is a good warning to be aware of validation bias when googling. Here is a paper that cites comparisons of post-tensioned concrete bridges. From the paper:
"As an example, two optimal post-tensioned concrete box-girder road bridges located in an eastern coastal region of Spain were assessed... In addition, maintenance was optimized to ensure that the bridge complied with all the performance requirements during its life-span of 150 years."
>Most sources are saying 15-20 years for post-tensioned.
Which sources?
Not a structural engineer (but I have been site manager for quite a few post-tensioned bridges building sites), you may be confusing pre-tensioned with post-tensioned.
In pre-tensioned there is no difference with "normal" rebar, the steel is in direct contact with the concrete.
In post tensioned you cast the concrete embedding pipes where you later insert the cables, then you tension the cables and inject in the pipes (and around the cables) some sort of corrosion preventing mixture, this used to be a mix of cement + additives (very, very fine, no sand nor other aggregates), but depending on the project it can nowadays be also some mix of grease/wax (in this latter case cables can be de-tensioned, removed, replaced and re-tensioned).
So, unlike the pre-tensioned structures and common rebars the cables in post-tensioned structures the cables are better protected and less likely to suffer corrosion deriving from infiltration of rain or water, so that part of the structure is - in theory - less prone to aging.
Still, the cables only represent a part of the structure, the rest is "kept together" by "common" re-bar steel, and these are - generally speaking - nearer to the surface of the structure, so I would expect properly built post-tensioned structure to have the same life-span of normal reinforced concrete.
IMHO 50 years is a very low threshold for the lifespan of any reinforced concrete structure, including pre-tensioned structures, while post-tensioned should have - at least for the cables - a longer lifespan.
Anecdotally, the first bridges I contributed to build are now around 40 years old and show no particular signs of decay.
>I did a quick check, and it looks like rebar concrete has a lifespan of about 50 years,
The variability based on type of rebar and the environment it is installed in is too high to make statements like that.
Galvanized rebar in concrete in non-marine environment will last hundreds of years. The concrete will probably crumble around it before the rebar corrodes if there's any appreciable moisture and freezing temps. Epoxied rebar will last less, bare rebar less still and improperly installed epoxy rebar will last less than that.
There are tons of 100yo buildings in fairly moist temperate climates with (poorly, by modern standards) reinforced concrete foundation that used bare rebar and are doing just fine.
Gossip from a prominent building technologist is 40-80 years for mass produced concrete condos. 80+ years is expected lifespan, if all goes right. 40 is serious structural issues from corner cutting. This is in Canada with bad weather cycles. Usually civil infra has better oversight. It was... a lot less than I expected. But long enough to flip condos for a few more cycles until crazy contingency fees + insurance, which I guess is enough.
If that is true; how could I refinance my 30 year loan on a 20 year old post tension pedistal slab condo? And why isn’t replacing the slab in our reserves budget?
- according to two recent independent structural model calculations based on the original plans, the building that collapsed was deliberately designed to meet only 100% to 115% of the original static loads to save money, but not the dynamic loads of rolling vehicles or interior upgrades like granite counter tops and marble wall displays.
Also, there were a few 12" columns, no column caps, and not enough shear wall areas or elevator core tie-in to resist twisting from wind loads or prevent domino column failures.
- any number of events could have started the collapse because there was no safety margin, including water intrusion and previous hurricane wind loads, but it was probably vehicles rolling around the lobby level near the pool.
To answer your question, it would cost more than the building was worth to replace the columns and slabs. The 40-year review for that building really meant a teardown had they redone the structural model. The owners were already looking at a $100,000 to $200,000 bill each for cosmetic repairs. Because of absentee owners (lessors and airbnb), that level of investment for a rebuild doesn't fly.
It's believed that the former building inspector gave a positive building review speech so that cronies could continue selling units, as negative news would have to be reported to potential buyers, killing any sales.
Note that builders who looked at the post-collapse photos even one day afterwards all wrote, "Nothing looks right in those fotos." What bothered them the most were the columns that punched through with no debris stuck to the top (pejoratively called "those toothpicks"), and yards of rebar bundles that also looked too clean.
So as usual the chain of failures is a lot longer and more complex than the "cheapskates ignoring maintenance to save a few pennies" narrative you get on the internet.
Post tension should not decrease the lifespan, if anything in some applications it could increase the lifespan since there can be smaller or less cracks, which is easier to maintain. Maintenance is the main requirement to get 100+ years in a normal environment.
If you can get an economical, efficient route from co2 to graphene, using graphene flakes in composite materials might be an excellent method of carbon sequestration.
Steel and concrete have similar thermo coefficient of expansion factors, while fiberglass does not. Thus fiberglass rebar works in temperature stable environments, but if the temperature changes a lot it is prone to failure.
The above is a generalization. See a proper engineer if you are actually building something to get the correct details for your application.
Roman concrete and general architectural prowess should be a hint that technology is not always improving over time.
It baffles me that people studying the longevity of Roman concrete tends to attribute it merely to luck… Since when astonishing technology performance is found by luck? I think it is was more likely found with a lot of experiments and progressive improvements over centuries.
The world doesn't reward long term, unfortunately.
Today, if someone wanted a building or house built, and one person who knows a special formula and method gives a higher number than someone with rebar and concrete, they lose the contract.
I'd imagine in all industries, brilliance has been defeated by cheaper adequacy to some extent. I can think of a few examples offhand, all related to metal and tooling.
It's sadly been a race to the bottom, rather than sharing enlightening secrets.
Do you think that the common people of Rome, when given the choice between a house that'll last for 50 years, and a house that'll last for 2000 years but costs a multiple, would have chosen the latter? How many houses from ancient Rome are still standing today?
Taking this into consideration, do you still think that optimizing for the foreseeable future – as opposed to hundreds/thousands of years into the future – is a modern phenomenon? Do you think that the Romans, had they had ready access to today's technology (steel rebar, Portland cement, and the knowledge necessary to use it), would have built the Colosseum the way they did? Or did they build it that way out of necessity, because they lacked alternatives?
"do you still think that optimizing for the foreseeable future – as opposed to hundreds/thousands of years into the future – is a modern phenomenon?"
We literally he have proof written in stone. The wealthy men of olde were generational land-owners. They had dynasties and build generational assets. Their manshions and castles are still standing today unless they were destroyed by war. That was their wealth.
I have a friend who offers climate change risk assesments on infrastructure and industry. Once he told the investor his asset will be gone in 15 years, you know what he replied?
"Why do I care, i will sell it in 3 "
You couldn't do that kind of shit before. Today's wealth is held in invisible, imaginary assets, that you can flip and swap at the click of a button. This short-termism will be our undoing
No, we don't. Only a tiny fraction of ancient Rome's buildings are still standing ("standing" is relative, most of those are ruins). And they didn't overbuild them because of their virtuous character, but because they lacked more efficient construction techniques and materials.
> mansions, castles
Castles have been useless for hundreds of years now (except as tourist attractions), and a mansion that was built 300 years ago doesn't satisfy today's requirements (like built-in running water, indoor plumbing, electricity, insulation, accessibility). It seems that building something for eternity isn't actually a good use of our resources.
(Please note that I'm not defending the extreme short-sightedness demonstrated by that investor you quoted)
Survivor bias is calling. I can show you literally hundreds of old mansions and castles in my region that weren't destroyed but simply deteriorated over the centuries because their owners couldn't afford the upkeep anymore.
It's a myth that all old buildings were magically built to last for centuries. Most buildings simply decayed and only very few survived over the centuries and most of them due to constant rebuilding and maintenance.
> I think that Architecture is the most visible beacon of civilization, and I don't like what it tells us about ours.
This is a very one-sided view. The same argument can be used with other items as well, say shoes for example. Sure 200 years ago shoes were much more durable, but they were also so expensive that not everyone could afford them.
Same goes for housing. Sure, you can build beautiful long lasting houses today, but they'd be even less affordable than the modern "ugly boxes". Then there's changing requirements as well. I live in a 100+ year old house and while it's medium to smallish by today's standards, it used to be a twin house back when it was built...
In the original layout, rooms were tiny by today's standards not to mention insulation (or lack thereof), heating (wood and coal ovens in every room instead of central heating etc.), fire protection and plumbing.
It's much more expensive to modernise an old house and bring it up to code than it is to build a new one that's designed to meet all current requirements from the start.
Tiny houses were built for the poor.
Have you visited Regency style first-floor apartment? They are far from tiny, with up to 4 meters heigh ceilings, very large rooms...
I could just as well state that US McMansions are built for the poor because $100 million 25000ft² estates exist.
Yes, the super rich had big houses. But I'm not talking about the top 1% here. The average citizen throughout the centuries didn't reside in large houses or apartments. By your standards 99.x% of the people have been and still are poor.
Another example is their mastery of acoustics.
I remember visiting ruins of Roman amphitheaters when I younger, and getting surprised at how they had managed to design them so that the audience would clearly hear what was happening on stage, even from great distance.
I was told it was not entirely clear to us what key principles they were following to get the acoustics working so well and that a lot of their wisdom had been lost to us.
It was like 25 years ago, so I hope we've made progress in rediscovering some of these techniques. But still...
We've lost wisdom from ~200 years ago, never mind 2,000 years ago.
If you look around architectural preservation forums and publications you'll find lots of examples of people trying to preserve historic buildings and doing more harm than good by using modern materials. We forget why things rot, we forget why certain paint formulations are better than others, we forget why certain mortars are for certain bricks (that's a big one, lots of old buildings are rendered worthless by a tuck pointing job with modern concrete that breaks all of the bricks in the first couple of years), the list goes on and on.
Oh, no, we actually know these techniques really well.
Even a quick Google search for "theatre acoustics design" shows a lot of cool stuff.
Often, modern buildings are just lazily designed. Kind of like houses that forego hundreds/thousands of years of ventilation knowledge because you can just slap A/C everywhere.
I think it's attributed to "luck" because the Romans didn't have the theory or the tools necessary to do a systematic search of the problem space and didn't understand why one way of doing it is better than another. It's similar to ancient metallurgy, where we know that some quite impressive results were produced sometimes, but the artificers themselves didn't know exactly why their product was better than the product two countries over.
> Keep in mind though that the well-built structures are also going to be the ones which survive the best.
This is of course true, but the amount of buildings still standing is large, not small. And there are plenty more that were purposefully destroyed, or that collapsed during huge earthquakes.
It's not like we're fawning over one temple or palace. There are aqueducts, temples, houses, bridges, fortifications - so many.
Not to mention things like the Hagia Sophia, the largest church in the world for about 1500 years, built in 5 years.
"Hagia Sophia, the largest church in the world for about 1500 years, built in 5 years."
Today it would take 25 and be 250% overbudget, and then require repairs because subcontractor of a subcontractor of a subcontractor fucked up somewhere. And then the IT system in charge of doors wouldn't work.
I honestly don't believe that any country on Earth today could make a massive habitable structure that stands for >1000 years in an earthquake area in 5 years.
I have to completely disagree with this. We absolutely can make better concrete. In fact, we can make cars super fast, super reliable, and bulletproof too. The question is - why would we.
Things cost money. The hoover dam is made of concrete, is a hundred years old, and is doing just fine. For most concrete applications we are comparing the roman construction to, we use a balance of cost and utility. And here's the fun thing: when we need much better structural integrity, we don't even use concrete, we use other things.
So this question then becomes "the puritans had better horse carriages than we build now, why?" Well, it's not because we can't build a better horse carriage. It's because when we need to move a lot of heavy things, we use a truck.
There is no demand for expensive long-lasting concrete, except in rare cases like a big dam - where we do use long-lasting concrete.
And yes, Roman concrete was luck, not science. Because they have very little understanding of material sciences compared to what we know now. In fact, if I remember correctly they built a bunch of stuff out of sandstone, which burns, and burned down Jerusalem. But I may be misremembering something the tour guide said.
The fact is, without material sciences, you simply cannot run a bunch of experiments using trial and error to test things for over a century. Because while they improved over centuries, they could only test a couple of things to last those centuries (because you have to wait a hundred years for the results).
Lots of cultures tried concrete. One got it randomly right. There are people that go to a hundred palm readers, who all say random things. They find one that correctly predicts an event. Their takeaway is "that palm reader is real." That's called survivorship bias.
Old stuff is fun and mythical. They discovered some very basic facts about the universe. Extremely basic by modern standards. Their top scientists did what kids in 9th grade now know. Saying otherwise - that's just romanticizing the past.
I guess limestone is what I mean, not sandstone. Giving it a quick google, they used lime, and their brick/concrete structures did burn down because of that. My tour was a long time ago.
>so by your logic we are even dumber
I never said the romans were dumb, but the logic of putting dumb words in someone's mouth then sarcastically making fun of those (your) words, is quite dumb indeed.
by my logic, we are not dumber, and I already explained that. When we need things like fire retardants, we use many materials that are better than lime. It took burning jet fuel to bring down things we don't want to burn. We learned that lesson from the Chicago Fire. For residential homes, in communities with fire departments, it is not cost effective to have more than basic fire proofing.
It would indeed be dumb to build a fireproof single family home for double the cost, when the new owner is going to knock it down and build something else 50 years later. This is why we don't build skyscrapers out of wood though.
The first hit on Google for that string disagrees with you so perhaps you did misremember:
"Sandstone is non-combustible and thus resistant to fire, making it a preferred option for building and construction. Due to its natural density, fire takes longer to burn through sandstone blocks, meaning any homes experiencing a fire will have added time."
I think that most of our top engineers would not be able to do what Eratosthenes did with a wooden stick and some calculations (calculating the earth circumference and tilt).
Of course we collectively have much better Science today, but at the individual level I don't think we are smarter in any way.
And we tend to underestimate the wisdom that is lost after each generation.
Why do you think the USA was able to send people on the moon in 1969 but is struggling to do it again now?
And if fish had bear fur, they'd have bear lice. The conversation or claim is not about how smart someone is, while artificially limiting the resources they are allowed to use to come up with a solution. We can model chemical reactions on server farms at a subatomic level. We have learned knowledge and reference materials. An engineer would use all of those things. Whether they'd be able to use a stick and an abacus to calculate circumference and tilt is irrelevant. What is relevant, is we now are able to do it much faster and more precise, using our tools and knowledge, than they did back then with a wooden stick. When materials scientists come up with construction materials, they would use all that is currently at their disposal, and would and do achieve much better results than Roman concrete.
>but is struggling to do it again now
because no one is struggling. we have a much lower budget now because there is no cold war race to the moon, and the problem now is not "get to the moon at all cost" but is "get to the moon under this specific costs." The reason it's been a long work in progress, is because it's not urgent, and we want it cheap. Different problem, different solution. It's not because we don't know how to use a wooden stick.
> I think that most of our top engineers would not be able to do what Eratosthenes did with a wooden stick and some calculations (calculating the earth circumference and tilt).
Sure they would if you gave them time. Eratosthennes didn't just go do it, he spent some (how much we don't know) thinking about the problem. Engineers today have all the math background needed - they are a little rusty but if you give them a few days they can reconstruct the needed math.
Note that I gave them dedicated time to focus. I couldn't do it before lunch (in about an hour as I write this), but give me a few days to run some false starts and I think I could figure it out.
It's unlikely the Romans fully understood the chemistry behind the concrete they created and instead relied upon centuries of trial and error to perfect their mixes. Beginning with their insistence on using pozzolanas found near and around Mt. Vesuvius.
Those pozzolans were so important they were transported by ship from Naples to Caesarea and preferred over local materials to make the concrete studied there today.
Marie Jackson's research over the past twenty-thirty years has been stunning and quite simply, is a gift to the world.
I was pleased to see her mentioned, quoted, and continuing to perform her understated yet very valuable research into Roman Concrete.
>It's unlikely the Romans fully understood the chemistry behind the concrete they created and instead relied upon centuries of trial and error to perfect their mixes.
Some of the greatest achievements were perfected by trial and error. It is a valid way to build things.
People think things get invented by white coat wearing "scientists" in a lab. The reality is it was always tinkerers and inventors, the scientific models and explanations came after.
Why is it that we have given up on building beautiful buildings and cities? I suspect one factor is that we moved from a culture based in craftsmanship to university-educated architects.
Well, growing up I remember my grandparents describing how they used to get milk, soda, beer and household chemicals in glass containers instead of plastic. I grew up long after that was common, but as a kid it was still profitable to collect the glass soda bottles I found and return them for the meager deposit fees to buy stuff. Now everything is in single use disposable plastic containers and there are microplastics in everything.
It was more common to repair rather than replace things like vacuum cleaners, TVs and small appliances in my youth, now everything is disposable and tossed in the landfill as soon as it breaks.
I remember reusing paper sacks when we went to the grocery store instead of single-use plastic bags, and even if they weren't reused they could be used to collect compostable
waste in the house and just tossed in the compost pile for the garden to break down with all the other organics if they weren't used in some other way - but even just tossing them away was arguably more sustainable than the plastic bags we used today.
Professionally, I've worked on efforts to automate warehouse work and the business continuity strategy is always "they can use the manual process from before" except that within a less than a year many don't remember the manual process, no new staff was trained on the manual process and even if someone was still on staff that knew the manual process chances are it's no longer even possible due to other system changes. Then something happens that takes out the automation for a day or two. You even see echos of that in the current Just in Time supply chain issues many companies are experiencing. The automation is good because it enables improved pick rates but the skills to work without the automation are lost quickly, my point to the business has always been you need to practice without the automation though unless you want to accept shutting down all warehouse activity when systems go down.
"It's unlikely the Romans fully understood the chemistry behind the concrete they created and instead relied upon centuries of trial and error to perfect their mixes."
We don't fully unserstand quantum mechsnics, but have working CPUs.
I see that we have known for more than a decade how the Egyptians could have used a form of concrete to make the blocks the pyramids were made out of, to mold them at the point of use. (It involves crushed limestone and clay.) But no one talks about that. Presumably, the (precursors to the) Incas could have done the same, explaining how they fit their odd-shaped stone blocks together so tightly.
Is there any reason not to use the same method for modern concrete, instead of the enormously polluting method used today?
Egyptian pyramids might be more controversial, even though it makes a lot of sense that the clocks would have been molded in place from concrete. The large granite blocks inside the pyramid don't seem to be concrete based.
The South America sites with extremely precisely fitting, non-rectangular shaped blocks seem to have been very highly likely formed by using concrete and carved later. Cusco walls, Sacsayhuamán or bottom layers of Maccu-Picchu walls.
The site of Baalbek on the other hand suggests that ancients had the ability to lift up 1000 tons stone blocks. The nearby quarry with unfinished stone blocks shows that these were not formed using cement.
Perhaps the Eyptian pyramids were a mixture of methods. Perhaps some of the blocks were lifted up to position using an elevator like mechanism (the long pyramid side shafts without stairs), but then the regular blocks made with the concrete method. The "elevator" shafts don't go beyond half of the pyramid, so the idea of transporting large blocks all the way up is less compelling than using concrete.
It is clear that various ancient peoples also moved large rock objects wholesale. Egyptians and Ethiopians cut, lifted out, and transported 500-ton obelisks. If you can move the obelisks, 70-ton granite blocks for the king's chamber, or the 100-ton empty boxes in Saqqara, are smaller projects.
Whoever placed the 1000-ton trilithon blocks (before the Romans built temples on top) cut and moved them whole. The Baalbek temple entablature are, to my knowledge, the only example in the whole Roman Empire of handling rocks of more than 300 tons. Even when Rome looted Egyptian obelisks, they had to bust off the bottom third and leave it behind. So, I guess they had local help for Baalbek.
The pre-dynastic Egyptians were cutting rock as hard as corundum (ruby/sapphire aggregate) like butter to make dishware, tens of thousands of which ended up in graves. The method was apparently lost before the pharaohs. It's not hard to understand technology being lost; but how it came to be invented first is a mystery. And, what exactly it was they invented, because we don't know. Archaeologists seem to lack any interest in finding out.
It's amusing to look into. Checking is not so easy - the concrete looks just like natural material. Finding an object embedded in the stone would prove it.
It's easy to prove that ancients were unable to produce concrete. You just need to prove that they had no access to stone, fire, and water — the key ingredients required to make concrete.
One building that always gets mentioned when it comes to Roman concrete (not in this article though, so I felt compelled to add it) is the Pantheon (https://en.wikipedia.org/wiki/Pantheon,_Rome), which is only ~100 years younger than the tomb of Caecilia Metella and features the world's largest unreinforced concrete dome (43 m / 142 ft diameter).
Before we start comparing Roman concrete structures to modern ones, we have to consider that there's a heavy survival bias here. We're only looking at Roman concrete structures that happened to survive for 2000 years while most Roman concrete structures probably didn't survive.
What I found interesting about Roman cement is that it was ironically softer than modern cement and had an almost self repairing property, think of ancient docks that had constant waves wearing it down yet lasted hundreds of years.
How do you think the quay walls in medieval Dutch and Flemish harbours were built? The mortar was made with Trass [0], a natural puzzolanic from the Eifel, transported along the Rhine.
"Roman cement", also known as hydraulic lime [1] mortar, was in widespread active mainstream use in many places in Europe until the 1920's, and in some the 1930's. In Latvia for example, large scale Roman cement production only came to an end with the second world war flooding specific quarries.
The main problem with these hydraulic cements is they cure/set much more slowly. That's very much guaranteed to limit their use in speed focused modern construction.
There's still a market for hydraulic lime mortars. There's even a euro norm for it, EN-459. These products have excellent breathability and moisture resistance properties. The entire field is seeing a revival in monument restauration and ecological construction. Most straw bale construction in Europe for example is plastered using hydraulic lime plasters.
Some interesting products:
- natural hydraulic limes (NHL), like Saint-Astier from France
- formulated/artifical hydraulic limes (HL), often using blast furnace fly ash
- natural puzzolanic additives, like trass from the volcanic Eifel, has been used continuously since the Roman era!
[0] https://en.wikipedia.org/wiki/Trass
[1] https://en.wikipedia.org/wiki/Hydraulic_lime