Nice article, and this is certainly a topic that everyone should know a little about seeing how fundamental cement is to our civilization. But it left out something very important at the end there... steel reinforced concrete is fantastic stuff of course, but it also comes with a drawback that is about to cost us very dearly; it doesn't last very long. All of our magnificent bridges and fantastic architecture come with a built-in expiration date because the steel inside them is rusting. That expiration date is somewhere between 50 and 150 years, and for a lot of our infrastructure it's coming due.
Concrete made from portland cement is waterproof but it isn't moisture proof, nor airtight. It breathes just enough that the oxidation of steel isn't completely stopped. And when the rebar rusts it expands, which causes the concrete to crack, letting more moisture and air in, causting the rebar to rust faster.
There are solutions to this problem, such as using rebars made from materials less susceptible to rust (stainless steel or even carbon fiber), but for the most part they are either a lot more expensive or nowhere nearly as strong. And there is susprisingly little research into this considering how important it seems... our civilization isn't very good at committing resources to things that have payoffs longer than 50 years, so everyone continues to use plain old steel as rebar in their constructions.
Meanwhile, the Roman pantheon remains standing, perhaps another couple of thousand years?
Basalt fibre reinforced concrete looks promising. The tensile strength is greater than steel rebar, and inexpensive when compared to carbon fibre. The environmental impact is much lower, as it's a melting process similar to fibreglass production, rather than smelting.
I get the impression that the continued use of steel rebar is less because there aren't superior technical solutions, but because there are significant regulatory, training and qualification hurdles. Use of non-steel rebars seems to complicate projects, and is only justifiable in special situations. Steel is usually adequate when appropriate anti-corrosion measures are taken (such as coating the rebar in epoxy).
Actually epoxy coated rebar has pretty major debonding issues in practice. If the epoxy coating was continuous then sure, but realistically during bending, cutting, tying, etc you're basically guaranteed to introduce scratches through that thin epoxy layer and once that steel starts rusting it'll tend to spread under the surface causing more cracks in the epoxy and allowing more corrosion.
>Adhesion loss of the epoxy coating to the steel surface was detected in all but one deck
that was 4 years old and older. The epoxy coatings were debonding from the reinforcing bars.
Whereas a bonded coating can be expected to protect the steel, a debonded coating allows
chlorides, moisture, and oxygen to reach the steel and initiate a rapid corrosion mechanism.
Reinforcing bars in various stages of adhesion loss showed visible signs of a corrosion process
underneath the coating, suggesting that ECR will provide little or no additional service life for
concrete bridge decks in comparison to bare steel. Other systems that will provide longer
protection against chloride-induced corrosion of the reinforcing steel with a higher degree of
reliability should be considered.
Counterpoint: Why do we need or even want anything to last a thousand years? In a hundred years we'll probably have much better technologies than today, and hopefully we'll be much richer. Why not rebuild stuff?
(I don't 100% buy this myself, just challenging the premise)
I actually think this is a good question and there are arguments on both sides:
pro-lasting: there are plenty of places with buildings that are hundreds of years old that are perfectly fine and useful buildings and there's no really compelling reason to tear them down and rebuild them.
Another argument is that the longer stuff lasts the less you may need to maintain it. Given that maintenance costs are hard to figure out and it's hard to get dedicated budget to keep things going (the present problem in the U.S. w/r to infrastructure for example), it's unlikely that things will be well maintained throughout their potentially useful life. If the stuff just lasts better, it's more likely to have a longer useful life...which is simply cheaper.
pro-replacing: An awful lot of national GDP in many countries comes from construction projects. Keeping a constant turnover in infrastructure and housing keeps huge populations employed with decent paying jobs.
Cities don't always have an infinite utility. The U.S. Rust Belt is an example of many cities that may have outlived their intended utility. This means that populations will migrate to cities with more current utility and the need to rearrange those areas to suit the change in population is important. A fixed or stagnate inner core, that could be replaced with higher density housing, is preferable than simply sprawling out elsewhere.
The follow up from this year (2019) https://rootsofprogress.org/cement-redux is even more interesting. It also mentions the DARPA effort to re-discover the formula for Roman maritime cement which gets stronger in sea water rather than erodes in sea water.
If we can figure that one out we could make concrete hulls for ocean going ships that would last many lifetimes.
There are concrete ships. Often these are barges, though traditional sail and powerboat designs are found (news to me as I wrote this comment, see Wikipedia link below).
I don't know how well the Roman formula would hold up, but traditional concrete tends to spall badly in constant exposure to salt water. Reinforced concrete suffers from rusting of the steel rebar segments.
Under dynamic stress, I doubt you'd get lifetimes of wear. Though several decades should be reasonably viable.
I thought I read recently that the 'secret' to Roman Cement - was that they were using volcanic ash, which changed the composition and resulted in a better ingredient.
Yes and no. The linked article explains that the 'secret' was ash from Mt Vesuvius which added silicates. But the Romans had another cement called "Maritime Cement" which is mentioned in the second article (the follow up article that I linked) which says,
"There does seem to be one particular application in which the Romans had a formula we would like to rediscover: maritime concrete, exposed to seawater. Normally, concrete in a pier or harbor erodes over time, both due to the salts and other minerals in the seawater, and due to the abrasion of sand and silt. However, some Roman marine structures have survived for 2,000 years. Geologists studying Roman concrete have recently discovered (2017) that the particular concrete formula used in those structures has a beneficial interaction with seawater, creating new crystals within the cementing matrix that actually increase strength. DARPA just announced that “Unlocking the Secrets of Roman Concrete” is one of many topics for exploration under a research awards program."
Is it substantially better than modern concrete with seawater-proof reinforcement? Stainless steel rebar, fiberglass rebar, and basalt rebar all exist. The latter sounds quite promising if you believe its manufacturers’ claims.
(A major cause of failure of concrete near or in the sea is that the rebar corrodes and expands, cause the concrete to break.)
Yes it is substantially better because it grows in sea water. Which is to say that it is self healing with respect to erosion. They give examples of roman maritime concrete that is over 2000 years old and still functional. No existing concrete does this (hence the DARPA call for research topics).
It is also why a concrete hulled boat using this stuff would not suffer hull erosion like the existing cement fleet did during world war II and afterwards.
It isn't clear to me (but I've not found a good paper on Roman "maritime" concrete either :-)) how it interacts with barnacles and other marine life.
It won’t crack like cement. It doesn’t require any special chemicals like cement. Doesn’t need to be shipped anywhere...
At least not... as much of it. If you built a rammed earth structure you will use a little cement actually. So everything that’s in cement, there will be a little of it in your rammed earth home.
But mostly you’ll just use readily available local-ish materials. Now for the benefits:
- Will last 1000 years
- Perfectly finished on the inside and outside with no fussy carpentry, mudding, or painting
- Thermal mass for free
- Load bearing
- Sheds water
- Breathable
- Insects won’t bother
- Basically as strong as stone
- Stunningly beautiful
- Largely free of odd vapors and perfumes
I am a fan.
There are downsides. It’s not right for every application. It is labor intensive. And it’s skilled labor bordering on artistry. But from my research, it’s the ultimate wall there is.
You aren't exactly correct. Cement is a binder. Cement can be used to bind rammed earth. I think you mean to say "Concrete." There is a difference.
Rammed earth will crack in a flat application just like concrete, which also will not crack as bad in a wall formation as it will in a flat foundation type application. This is due to rammed earth and concrete having excellent resistance to compression, as gravity does to a wall, but they are both weak in tension.
Sometimes rammed earth does require binders like I said before depending on locally available materials. There is fussy carpentry involved because you need to make forms for the walls within which you ram the earth.
It's not as strong as stone, unless you use the appropriate binders and you should get your finished product tested for strength before using it in a load bearing capacity.
It's still a good building material, I do agree with that, but it is not just as good as concrete and it only approaches the strength of concrete when cement is used as a binder. No readily available natural materials come close to the strength of cement bound aggregates.
Not totally weather resistant. And you likely need to stand it up on stone, or waterproof foundation. Walls need good capping. Good eaves help, but once you are at this kind of structure, tmberframe or concrete column, with any old in fill may do.
Many modern concretes are blends, papercrete, hempcrete, timbercrete, benefit from breathability.
Rammed earth at least benefits from reusable form work. And I reckon could easily be automated.
Clay and straw is a classic too.
A mix of materials a good idea, especially given building sand scarcity and environmental destruction.
Primarily, I agree that concrete is easier if you are looking for a “no brainer”, just pay someone and forget about it type project.
But if you are willing to do some more leg work to find good people and can afford to pay them, rammed earth will be a better result for most small (<10,000 sqft) “sub-urban” applications.
I am in the planning stages of building a 25 foot obelisk on my property. I was planning to use concrete and hadn't heard of rammed earth. Is rammed earth an appropriate material for my project?
(Everything thinks I am joking about this but I am 100% serious)
> Interest in rammed earth declined after World War II when the cost of modern construction materials decreased.[citation needed] Rammed earth was considered substandard, and still is opposed by many contractors, engineers, and tradesmen who are unfamiliar with earthen construction techniques.[7] The prevailing perception that such materials and techniques perform poorly in regions prone to earthquakes has prevented their use in much of the world.[citation needed] In Chile, for example, rammed earth edifices normally cannot be conventionally insured against damage or even be approved by the government.[citation needed]
Lots of missing citations, but seems reasonable. I for one had never heard of this construction technique until today.
I never realized that "quick" means "alive" in quicklime, quicksilver.
It's interesting because I now see the same pattern is used in old italian (mercury is "mercurio" but also "argento vivo", living silver, and calcium oxide is "ossido di calcio" but also "calce viva", living lime).
As far as I understand, in hungarian ("fürge ezüst" -> "lively silver") and german ("quecksilber" -> quicksilver) the same pattern exists for mercury, though I didn't find the calcium carbonate equivalent.
I imagine there is some shared (alchemic?) tradition there, and I wonder what other "alive" things exist.
> [...] german ("quecksilber" -> quicksilver) [...]
In German, there's also quicklebendig – meaning "lively", "very active" – compared to lebendig, which means "alive", "living". It's slowly becoming outdated, though.
It may be obvious to those of us with an interest in etymology, but when the phrase came up in my tabletop gaming group (ages 18-50), they were unanimous (save for myself) that the meaning was "the fast and the dead". I had to resort to a web search to convince them otherwise.
One reason that steel and concrete work so well together, with concrete handling the compression loads and steel handling the traction loads, is that they have a very similar thermal expansion coefficient. Thus, when the temperature changes both components expand or contract at the same rate. Just think of what would happen if they didn't.
Nice article. Cement’s climate footprint is really big though, so we should be using it in construction much less than we’re doing now. Glulam is the future.
I was surprised to see that the lime cycle itself is carbon-neutral, if I am reading it correctly. Is cement's footprint due to the energy required to make it? Or is the chemistry of portland cement not carbon-neutral?
Maybe, but that's not how it's done today, and it's not the sort of thing you change overnight.
Complicating matters is the fly ash component of modern concrete. Fly ash can replace 50% or more of the portland cement in concrete. Fly ash is a byproduct of burning coal. So when you replace the coal plants with solar arrays, you need to create even more portland cement than you would need to if you were burning coal (and using the subsequent fly ash in your concrete.)
The latter; slaked lime will reabsorb the same amount of CO₂ that was released in its calcination, but portland cement absorbs much less. Moreover, the amount of CO₂ released in the calcination process itself is much larger than the amount released to produce the energy for it, even if you use fossil fuels.
Plantation grown timber is a very different proposition compared to logging an old-growth forest.
Frankly you don't have as many trees around you as you think you do (and you're probably a lot more dependent on them then you realize since local forests are usually performing an important ground support function in preventing hillsides washing away in the rain).
No environmentalist is opposing sustainable plantation timber operations, and there's plenty of those going on everywhere.
If they live in the US they probably don't live near much old growth forest.
For instance, nearly all of Michigan was logged. Someone driving through the state might not think so, but most of the trees here grew back after that.
Frankly, you shouldn't assume you know how many trees are around me.
Plantation grown and old growth are very different. Just because it is a forest doesn't mean it is old growth.
I have a lot of trees and the State land next to me has even more that need thinned. I've thinned out my land for better forest health, better wildlife habitat and to reduce fire danger. The State would do well to do the same, but I is very hard to log anything but private land around here.
What happened to my logs? They went to a mill and some for pulp. They weren't old growth, that was gone long ago, but new products like CLT can make use of smaller trees.
Plantations are great, but this whole county grows trees like crazy. It isn't hard to look around and find something that can be logged in a response way, but getting approval is near impossible.
An industrial logging operation fells and transports about 4 trees an hour. Let's assume about 5 productive hours in a day which is on the conservative side. So 20 trees per day. 100 per week. 1200 every 3 months.
So a single commercial logging operation is going to be able to clear cut 2 acres of dense forest every 3 months - which will then be just gone and not coming back with any type of biodiversity or wild life for at least 10 years probably longer if ever since we're not talking plantation growth here.
It is out out of touch arguments like this that prevent good management of many of our forests. We can have healthy forests, jobs and resources to build with, but when people too far away sit around with a calculator and make a decision, we don't get any of them.
All your math doesn't change the fact that there are too many* trees in my area.
1 square mile is 640 acres. At 8 acres per year, this is 80 years to get back to the beginning! I would have expected that commercial logging is much faster because 8 acres is not much!
They go much faster than 1 tree every 15 minutes. It will of course vary based on the terrain and size of the trees, but watch how modern operations work:
I think trees are a fantastic building material. If left to rot in nature, much of the carbon will slowly be released back to the atmosphere. The carbon sequestering abilities of trees also slow down after a certain age.
Now this doesn't mean we should clear-cut old forests, or only have short-lived commercial forests. I think we should aim to have mostly natural forests with trees of different ages, up to hundreds of years, and use selective logging instead of clear cutting.
Timber buildings can last hundreds of years. In such buildings, using timber is a great carbon sink. Interestingly, it's the glue that will deteriorate before timber does.
I do love the theory, and the elevator pitch makes a lot of sense. Unfortuantely I don't have the bandwidth to really dive into it like I'd like to, but I did find what seems to be a paper disputing his claims[0]. Below is the abstract (emphasis my own):
> Since 1974 Joseph Davidovits, a French concrete chemist, has been proposing that the pyramids and temples of Old Kingdom Egypt were built of geopolymer “concrete” poured into molds, rather than quarried blocks of limestone. We use geological evidence and engineering principles to demonstrate the flaws in this daring hypothesis. Pyramid and temple blocks show sedimentary bedding, burrows, and optical and SEM-scale properties characteristic of normal microporous limestones, and they are cut by tectonic fractures. Block dimensions and shapes are not likely to be the product of pouring into wooden molds, and some blocks show quarrying marks. It is not easy to give a geological education to a brilliant and determined chemist.
"Since 1974 Joseph Davidovits, a French concrete chemist, has been proposing that the pyramids and temples of Old Kingdom Egypt were built of geopolymer “concrete” poured into molds, rather than quarried blocks of limestone. We use geological evidence and engineering principles to demonstrate the flaws in this daring hypothesis. Pyramid and temple blocks show sedimentary bedding, burrows, and optical and SEM-scale properties characteristic of normal microporous limestones, and they are cut by tectonic fractures. Block dimensions and shapes are not likely to be the product of pouring into wooden molds, and some blocks show quarrying marks. It is not easy to give a geological education to a brilliant and determined chemist."
Of interest are speculations regarding how cement was discovered in the first place.
That is, why would one make a kiln to heat the rock? (A mere campfire won't cut it... doesn't get hot enough.) Some speculate it could have been a lightening strike on a slab of rock, investigated by an early human who discovered the resulting crumbly powder re-solidified with water. But, this seems very unlikely. Big mystery.
Calcite calcines to quicklime at 850°, which is red-orange. Mere campfires commonly reach yellow heat, which is over 1000°, and have often been used to cook shellfish, whose shells are made of calcite and can calcine to quicklime. So I suspect that the discovery of quicklime probably happened numerous times in mere campfires during the first three million years of human history called the Paleolithic. (There might have even been several independent nutcases who decided to experiment with the stuff even after they saw what it did to water.) Lime kilns, though not the same thing as campfires, were commonly wood-fired, even into the 20th century.
In the Neolithic, the humans were firing pottery, which often requires temperatures over 850°, depending on the clay body you're using. It isn't clear whether lime kilns predate the Neolithic, but if they don't, pottery kilns would have occasionally produced quicklime by accident until you figured out that you can't temper your pots with shellfish (or calcite-containing sand) if you're going to fire them over about 800°, which is not particularly difficult. (Modern earthenware is usually fired over 1000°.) That would have made the discovery of quicklime unavoidable, if it didn't happen earlier, and of course potters must spend a great deal of time investigating the properties of their materials and how they respond to firing.
I don't remember all of them, but one was that the dude left out the part of the alcohol-distillation procedure where you dump the liquid that comes over first, which contains most of the methanol. A lot of blues singers went blind from someone skipping that step, and people have died from it, too.
In general, he doesn't provide adequate information about safety precautions. The book is like an Anarchist's Cookbook for bootstrapping—anybody who tries its recipes without further information is likely to end up dead. It should be called The Misinformation.
The thing that got me was that when I told him that there were potentially fatal errata and where to look to see if they were already known problems, he said there was no public list; I should just take the time to write up the problems without knowing whether he already knew about them or not, and there was no way for readers to find out what errors had already been reported in the version of the book they already had. I think that says more about his attitude about accuracy than any particular error in any particular version of the book.
Concrete made from portland cement is waterproof but it isn't moisture proof, nor airtight. It breathes just enough that the oxidation of steel isn't completely stopped. And when the rebar rusts it expands, which causes the concrete to crack, letting more moisture and air in, causting the rebar to rust faster.
There are solutions to this problem, such as using rebars made from materials less susceptible to rust (stainless steel or even carbon fiber), but for the most part they are either a lot more expensive or nowhere nearly as strong. And there is susprisingly little research into this considering how important it seems... our civilization isn't very good at committing resources to things that have payoffs longer than 50 years, so everyone continues to use plain old steel as rebar in their constructions. Meanwhile, the Roman pantheon remains standing, perhaps another couple of thousand years?