6 ms·

About Roman cement, maybe we know how it was made, BUT for a number of reasons we decided to use other types of cement that not necessarily are "better" than th

by jaclaz 4y ago

About Roman cement, maybe we know how it was made, BUT for a number of reasons we decided to use other types of cement that not necessarily are "better" than the Roman one, particularly when it comes to durability. The ubiquitous modern Portland cement and concrete made with it hardens faster and has initially a higher resistance. Modern Pozzolanic cements, more similar to the Roman ones, are in practice very rarely used, even if they have most of the properties of the old Roman ones (longer time to harden, hardness/resistance increasing over the years, generally much better resistance to water).

oblio 4y ago
Concrete made from Portland cement lasts at least 100 years and generally we don't need more. If anything, we want the flexibility of stuff that "only" lasts around 100 years, because you know, due to new tech and changing economies, we want to be able to model our cities periodically. And Portland cement is cheaper and can be made in much larger quantities. This is kind of a recurring story with these topics: we know how to make it "better", but we don't really need that "better", we do need "cheaper" and "higher availability" instead.
- trashtester 4y ago
  > Concrete made from Portland cement lasts at least 100 years and generally we don't need more. "We" may not need more (as en "we" that are alive today). But future generations would thank us if we would make structures that would last for 500+ years instead of 100 years. Much better for the very long term economy AND the climate.
  - jefftk 4y ago
    We don't have a very good idea what sort of structures people will want in 500+ years, and there are lots of better ways we can turn money into improving life for people centuries in the future (primarily in trying to reduce the risk humanity goes extinct before then).
  - hannasanarion 4y ago
    Would they really? Sure, having an old Colosseum or Aqueduct to look at is nice, but do you really want to live in a place where every single square inch of useful ground in the whole country is occupied by an ultra-resilient building that somebody thought would be useful 2000 years ago? We have all of these examples of nice long-lasting roman architecture because those are the examples that survived. Romans didn't live in the Colosseum and the aqueducts. The Romans built hundreds of thousands of other buildings that fell down on their own or were demolished for any number of reasons over the millennia.
    - oldgradstudent 4y ago
      You can always demolish unneeded structures. The Golden Gate bridge was opened 85 years ago. Is there any sane reason to demolish it in 15 years?
    - tinsmith 4y ago
      In support of this, we can even see the rapid changes in structural demands over half a century in a culture like the US. Suburban sprawl eats up spaces with any viable flexibility in a matter of years, and things like shopping malls fade out of fashion just as quickly as they entered it. In a relatively short time, we are left with brick & concrete hellscapes that are largely being abandoned because developers find it easier (and probably cheaper) to work with fresh land. This Disposable Mentality gets us into obviously environmental and economic messes so often that I am still flabbergasted that the US at large has not adopted a more Reusable Mentality, and incorporated some long-term thinking into their suburban planning.
    - trashtester 4y ago
      I said 500+, not 2000. If, 500 years from now, the best 25% of structures built by us remain standing, I think that's a good thing.
  - Denvercoder9 4y ago
    > But future generations would thank us if we would make structures that would last for 500+ years instead of 100 years. Would they? 100 year old houses are already dinosaurs in terms of energy use, and often it's a lot easier and cheaper to demolish and rebuild instead of isolating and installing modern heating. I can't imagine how outdated a 500 year old house would be.
    - jaclaz 4y ago
      It depends on what elements you take into account. Demolishing a building and re-building it in terms of total energy (and/or emissions) is not free of costs, maybe you don't pay them directly, unlike heating or air conditioning, but they do exist. Right now 100 years old houses (the brick or stone ones, not the wooden ones, nor the reinforced concrete ones that are usually more recent) already exist and can be restored/upgraded (though of course with some limitations) with a minimal amount of work (in terms of energy and emissions). More or less the "if ain't broken don't fix it approach". Now, if we had some building material lasting only 100 years that could be manufactured with little expense of energy and low or no emissions, that would be another thing. If we imagine that (hypothetical) there is a form of (say) square section bamboo that we can grow at little or no cost and that we can assemble with (still say) some vegetal cement or similar, so that the results of the periodical demolitions can be reused or recycled or that is however biodegradable, then a short lived building would make much more sense.
      - Denvercoder9 4y ago
        > Right now 100 years old houses already exist and can be restored/upgraded with a minimal amount of work (in terms of energy and emissions). Having lived in one, I can assure you that upgrading such a house to modern energy standards isn't a minimal amount of work. Lots of these houses just have a single brick wall directly facing the outdoors. Insulating that means you have to basically completely strip the house down to the brick, and even then it won't be as good as new construction. Of course demolishing and rebuilding also takes energy; but if you amortize it over 50 years or so, I bet in the end you come out ahead. Building technology has improved a lot in energy efficiency over the last century.
- paganel 4y ago
  My grandma’s mountain village is located just below some big hydro dam (the second biggest in my country, Romania), built in the early 1960s. So that gives the authorities (or whoever will actually own that dam at that point) another 40 years to either tear it down completely for safety reasons (I don’t see that happening, the incoming money is too good) or to tear it down and build a similar one in its place (I also don’t see that happening, to be honest). And this is, comparatively speaking, a happy case, I’m sure there are lots of big dams built back in the 1930s in places like the US or the former USSR that are only 10 or so years from that “this concrete-structure is only guaranteed to last 100 years” time-point.
- jaclaz 4y ago
  Only for the record, the 100 (hopefully more) years life is expected in houses/buildings, more like 50-60 years if used in reinforced concrete structures open to the weather (like bridges and viaducts), then some maintenance/cortical rebuilding/consolidation is usually needed. This is not only due to the kind of cement, there are a number of other factors that have an influence on the (scarce) durability of modern reinforced concrete structures. Portland cement may be cheaper than pozzolanic in some markets/countries and the contrary may be true in some other ones, but you cannot anyway make a direct comparison, as they are normally used in different kinds of structures. The "let's build things that have a set expiry date" approach could be a very good one IF we actually knew how long a construction lasts (or should last) and matters would have been organized so that this continuous demolishing/rebuilding could be planned and carried on, but this is not what AFAIK happens anywhere, exception maybe for a few (BTW wooden) temples in Japan.
  - sbierwagen 4y ago
    >50-60 years if used in reinforced concrete Structures which need a longer design life than that have switched to stainless steel rebar, which currently has an unknown life span. Check back in a century or two.
kragen 4y ago
You say, "Modern Pozzolanic cements, more similar to the Roman ones, are in practice very rarely used". Wikipedia says, "Over the course of the 20th century the use of pozzolans as additions (the technical term is "supplementary cementitious material", usually abbreviated "SCM") to Portland cement concrete mixtures has become common practice. Combinations of economic and technical aspects and, increasingly, environmental concerns have made so-called blended cements, i.e., cements that contain considerable amounts of supplementary cementitious materials (mostly around 20 wt.%,[clarification needed] but over 80 wt.% in Portland blast-furnace slag cement), the most widely produced and used cement type by the beginning of the 21st century.[5]". https://en.wikipedia.org/wiki/Pozzolan https://en.wikipedia.org/wiki/Pozzolan Who's right? Are pozzolanic cements "the most widely produced and used cement type" or "in practice very rarely used"? I'm guessing it's the writer who doesn't think "pozzolan" is a proper noun in English.
- jaclaz 4y ago
  Portland is the most used. However nowadays it is rare that a Portland based cement is "pure" any Portland based cement may have pozzolanic components, i.e be a "blended" cement but the use of pozolanic components even in relatively large percentages does not make them "real pozzolanic cement" (but they are, when there are large amounts of pozzolanic components what I called "modern pozzolanic cement", the "base" is usually anyway Portland). "Real pozzolanic cements" are fabricated/created with a different process and from different base materials, they are not really used anymore, exception made for particular restoration works.

by jaclaz 4y ago

oblio 4y ago

Concrete made from Portland cement lasts at least 100 years and generally we don't need more. If anything, we want the flexibility of stuff that "only" lasts around 100 years, because you know, due to new tech and changing economies, we want to be able to model our cities periodically. And Portland cement is cheaper and can be made in much larger quantities. This is kind of a recurring story with these topics: we know how to make it "better", but we don't really need that "better", we do need "cheaper" and "higher availability" instead.

trashtester 4y ago
> Concrete made from Portland cement lasts at least 100 years and generally we don't need more. "We" may not need more (as en "we" that are alive today). But future generations would thank us if we would make structures that would last for 500+ years instead of 100 years. Much better for the very long term economy AND the climate.
- jefftk 4y ago
  We don't have a very good idea what sort of structures people will want in 500+ years, and there are lots of better ways we can turn money into improving life for people centuries in the future (primarily in trying to reduce the risk humanity goes extinct before then).
- hannasanarion 4y ago
  Would they really? Sure, having an old Colosseum or Aqueduct to look at is nice, but do you really want to live in a place where every single square inch of useful ground in the whole country is occupied by an ultra-resilient building that somebody thought would be useful 2000 years ago? We have all of these examples of nice long-lasting roman architecture because those are the examples that survived. Romans didn't live in the Colosseum and the aqueducts. The Romans built hundreds of thousands of other buildings that fell down on their own or were demolished for any number of reasons over the millennia.
  - oldgradstudent 4y ago
    You can always demolish unneeded structures. The Golden Gate bridge was opened 85 years ago. Is there any sane reason to demolish it in 15 years?
  - tinsmith 4y ago
    In support of this, we can even see the rapid changes in structural demands over half a century in a culture like the US. Suburban sprawl eats up spaces with any viable flexibility in a matter of years, and things like shopping malls fade out of fashion just as quickly as they entered it. In a relatively short time, we are left with brick & concrete hellscapes that are largely being abandoned because developers find it easier (and probably cheaper) to work with fresh land. This Disposable Mentality gets us into obviously environmental and economic messes so often that I am still flabbergasted that the US at large has not adopted a more Reusable Mentality, and incorporated some long-term thinking into their suburban planning.
  - trashtester 4y ago
    I said 500+, not 2000. If, 500 years from now, the best 25% of structures built by us remain standing, I think that's a good thing.
- Denvercoder9 4y ago
  > But future generations would thank us if we would make structures that would last for 500+ years instead of 100 years. Would they? 100 year old houses are already dinosaurs in terms of energy use, and often it's a lot easier and cheaper to demolish and rebuild instead of isolating and installing modern heating. I can't imagine how outdated a 500 year old house would be.
  - jaclaz 4y ago
    It depends on what elements you take into account. Demolishing a building and re-building it in terms of total energy (and/or emissions) is not free of costs, maybe you don't pay them directly, unlike heating or air conditioning, but they do exist. Right now 100 years old houses (the brick or stone ones, not the wooden ones, nor the reinforced concrete ones that are usually more recent) already exist and can be restored/upgraded (though of course with some limitations) with a minimal amount of work (in terms of energy and emissions). More or less the "if ain't broken don't fix it approach". Now, if we had some building material lasting only 100 years that could be manufactured with little expense of energy and low or no emissions, that would be another thing. If we imagine that (hypothetical) there is a form of (say) square section bamboo that we can grow at little or no cost and that we can assemble with (still say) some vegetal cement or similar, so that the results of the periodical demolitions can be reused or recycled or that is however biodegradable, then a short lived building would make much more sense.
    - Denvercoder9 4y ago
      > Right now 100 years old houses already exist and can be restored/upgraded with a minimal amount of work (in terms of energy and emissions). Having lived in one, I can assure you that upgrading such a house to modern energy standards isn't a minimal amount of work. Lots of these houses just have a single brick wall directly facing the outdoors. Insulating that means you have to basically completely strip the house down to the brick, and even then it won't be as good as new construction. Of course demolishing and rebuilding also takes energy; but if you amortize it over 50 years or so, I bet in the end you come out ahead. Building technology has improved a lot in energy efficiency over the last century.
paganel 4y ago
My grandma’s mountain village is located just below some big hydro dam (the second biggest in my country, Romania), built in the early 1960s. So that gives the authorities (or whoever will actually own that dam at that point) another 40 years to either tear it down completely for safety reasons (I don’t see that happening, the incoming money is too good) or to tear it down and build a similar one in its place (I also don’t see that happening, to be honest). And this is, comparatively speaking, a happy case, I’m sure there are lots of big dams built back in the 1930s in places like the US or the former USSR that are only 10 or so years from that “this concrete-structure is only guaranteed to last 100 years” time-point.
jaclaz 4y ago
Only for the record, the 100 (hopefully more) years life is expected in houses/buildings, more like 50-60 years if used in reinforced concrete structures open to the weather (like bridges and viaducts), then some maintenance/cortical rebuilding/consolidation is usually needed. This is not only due to the kind of cement, there are a number of other factors that have an influence on the (scarce) durability of modern reinforced concrete structures. Portland cement may be cheaper than pozzolanic in some markets/countries and the contrary may be true in some other ones, but you cannot anyway make a direct comparison, as they are normally used in different kinds of structures. The "let's build things that have a set expiry date" approach could be a very good one IF we actually knew how long a construction lasts (or should last) and matters would have been organized so that this continuous demolishing/rebuilding could be planned and carried on, but this is not what AFAIK happens anywhere, exception maybe for a few (BTW wooden) temples in Japan.
- sbierwagen 4y ago
  >50-60 years if used in reinforced concrete Structures which need a longer design life than that have switched to stainless steel rebar, which currently has an unknown life span. Check back in a century or two.

kragen 4y ago

You say, "Modern Pozzolanic cements, more similar to the Roman ones, are in practice very rarely used". Wikipedia says, "Over the course of the 20th century the use of pozzolans as additions (the technical term is "supplementary cementitious material", usually abbreviated "SCM") to Portland cement concrete mixtures has become common practice. Combinations of economic and technical aspects and, increasingly, environmental concerns have made so-called blended cements, i.e., cements that contain considerable amounts of supplementary cementitious materials (mostly around 20 wt.%,[clarification needed] but over 80 wt.% in Portland blast-furnace slag cement), the most widely produced and used cement type by the beginning of the 21st century.[5]". https://en.wikipedia.org/wiki/Pozzolan https://en.wikipedia.org/wiki/Pozzolan Who's right? Are pozzolanic cements "the most widely produced and used cement type" or "in practice very rarely used"? I'm guessing it's the writer who doesn't think "pozzolan" is a proper noun in English.

jaclaz 4y ago
Portland is the most used. However nowadays it is rare that a Portland based cement is "pure" any Portland based cement may have pozzolanic components, i.e be a "blended" cement but the use of pozolanic components even in relatively large percentages does not make them "real pozzolanic cement" (but they are, when there are large amounts of pozzolanic components what I called "modern pozzolanic cement", the "base" is usually anyway Portland). "Real pozzolanic cements" are fabricated/created with a different process and from different base materials, they are not really used anymore, exception made for particular restoration works.