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).
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.
"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.
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.
The Golden Gate bridge was opened 85 years ago. Is there any sane reason to demolish it in 15 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 I can't imagine how outdated a 500 year old house would be.
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.
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.
No, insulating that means that you add an extra set of layers to the outside of that brick wall, which can done without impacting the interior while the people are living in that building during the renovation.
You’ve never actually done this I assume? I have lived in a 1920s house during renovation. I wouldn’t wish it on my worst enemy. Should have torn it down; would have been better for the environment and my pocketbook.
I have, and there was a lot of drilling into concrete filled with tiny stones, that caused enough noise to cause pain in the ears. Only during working hours, though.
> would have been better for the environment and my pocketbook.
If you don't want to live in a building as it is being renovated, you can always rent something else for the time it takes. If the renovation takes less time than rebuilding, you also pay less rent.
The beautiful hand-carved crown moulding and stairs are nice, but not worth outrageous heating bills.
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.
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.
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.
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
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.
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.
Is this a myth I have fallen for?