Alternative materials could shrink concrete’s giant carbon footprint | Hacker News Reader

Alternative materials could shrink concrete’s giant carbon footprint

cen.acs.org

128 pointsarunbahl17 comments

I don’t get this article. There is a “CO2 is bad mm’kay” problem statement, then a recommendation of fly ash, which is already a common additive to mixes, then a recommendation for mill slag, which is already a common additive where it’s available, then a recommendation to look at geopolymers, which I’ve never seen specified for any job anywhere and which are also useless for cast-in-place applications, and finally a time-will-tell conclusion. Is this content for content’s sake? Anything remotely practical mentioned has been in use for years.

The problem with use of flyash in the West is mostly legislative.

The problem is that there are no two similar sources of flyash, as there are no chemically identical sources of coal from which it came from.

Current code only lets a very narrow selection of flyash to be blended into OPC, despite most of it being suitable, and not influencing the resulting characteristics.

For the geopolymers, the issue of natural variability is even worse.

Another problem with fly ash in Europe is that a number of countries have no coal fired power stations to produce it or are closing down what they do have. So it is a declining resource anyway.

As written in the article, the amount already there will last humanity at least a century.

Nice to see geopolymers mentioned. Geopolymers are becoming more common around the world. They can be formulated from local materials and in many cases have superior material properties to Portland cements. Joseph Davidovits of the Geoplymer Institute has been instrumental in the spread of his lifes work, geopolymers.

Davidovits also claims that many ancient megalitic constructions were made using geopolymers which fits with stories of technologies that soften rocks.

Geopolymer Institute is an amazing resource on the subject. https://geopolymer.org

Pyramids of geopolymer, https://youtu.be/znQk_yBHre4

I've only ever heard it being called geocrete but looking further now that seems to be a portmanteau.

> Geopolymer Institute is an amazing resource on the subject. https://geopolymer.org

I find it odd that so much of their front page and entire site is dedicated to defending the theory that the pyramids were made of man-made or re-agglometared stone. The hypothesis is mentioned in the Wikipedia article "Egyptian pyramid construction techniques"[0] under the hypothesis subsection but mostly dismissed:

    Dipayan Jana, a petrographer, made a presentation to the ICMA (International Cement Microscopy Association) in 2007[46] and gave a paper[47] in which he discusses Davidovits's and Barsoum's work and concludes "we are far from accepting even as a remote possibility a 'man-made' origin of pyramid stones."

Apart from that, the only other references to the theory or institute are in the Pyramidology article subsection Ancient astronauts [1] which references an article by Joseph Davidovits of the Geopolymer Institute:

    Several proponents of ancient astronauts claim that the Great Pyramid of Giza was constructed by extraterrestrials, or influenced by them.

Reading through all of this it comes off as fanciful and reminds me of reading those books about Ghosts, Bigfoot or Monsters in elementary school.

[0] https://en.wikipedia.org/wiki/Egyptian_pyramid_construction_...

[1] https://en.wikipedia.org/wiki/Pyramidology#Ancient_astronaut...

I would like to see independent corroborating analysis before accepting the hypothesis as fact. But re-agglomerated stone is a much simpler explanation than anything that has been posited so far. A little different but if you consider that geopolymers were known to the ancients the schist disk is less mysterious as well. One of the applications Davidovits sells is high temperature geopolymer composite parts. The parts are stone in shapes that would be impossible to carve or make in any other way.

https://www.materialstoday.com/polymers-soft-materials/featu...

I'm not discounting geopolymers as a viable technology, I just think dedicating the majority of your site to defending a hypothesis instead of promoting your technology is odd.

Also it seems like it would be pretty simple to prove or disprove the hypothesis scientifically but no one seems to care enough to try, which doesn't speak to it's credibility. Instead they argue about the provenance of samples analyzed 40 years ago and subsequently destroyed.

C.f. BBC article today reporting on British engineers urging the construction industry to stop knocking down houses because of the carbon emissions of new builds:

https://www.bbc.co.uk/news/science-environment-58667328

The 8% stat is surprising.

For housing, hempcrete [0] had shown a lot of promise with its insulating, anti-mold and moist repellent properties. Plus its CO2 binding and quite cheap.

[0] https://en.m.wikipedia.org/wiki/Hempcrete

It is not a replacement for any sane use of concrete. It could substitute for wall panels and insulation.

Mmmkay, but concrete could also shrink the global carbon footprint. Mixing CO2 to concrete makes it hardening much faster and the result gets more durable.

https://www.globalconstructionreview.com/researchers-find-wa...

Something that helps but is little-practiced is just making structures hollow. For instance instead of pouring 300 cubic meters of concrete for one of SFMTA's absurd high-floor boarding platforms[1], some agencies are building similar structures that begin by placing hollow, prefabricated, fiberglass boxes and pouring concrete around them, reducing the total concrete in the project by an order of magnitude.

A little bit of engineering goes a long way.

1: https://www.google.com/maps/@37.7801361,-122.3895982,39a,49....

The other very common approach (that has been used for millennia) is use gravel or similar fill.

Making the whole thing out of monolithic concrete would be really absurd - both from cost and from shrink cracking and similar issues.

Cracking is just a profit center for Tutor-Perini. If the structure lasts for more than a few years how are they going to get paid?

This article takes"pushing out content" to heart. I don't anybody familiar with the topic learned anything here

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