Riddle of cement’s structure is finally solved | Hacker News Reader

Riddle of cement’s structure is finally solved

news.mit.edu

123 points_isus17 comments

I love these base-level, practical advances where even a slight improvement in a formula (provided it is not closely guarded) can, say, improve the strength of a material by 5-10%, meaning that much less of it must be used, which at a scale like concrete's can make for huge changes in usage, markets, processes etc.

Concrete is a HUGE greenhouse gas source, so this is also a great boon for the environment. It's estimated that concrete is responsible for 5% of all anthropogenic CO2.

https://en.wikipedia.org/wiki/Environmental_impact_of_concre...

I hate to break it, but it could actually have the opposite effect by disproportionately increasing our consumption of concrete.

https://en.wikipedia.org/wiki/Jevons_paradox

At least we get more concrete out of it..

But that's not concrete.

There are more riddles to be discovered

https://en.wikipedia.org/wiki/Egyptian_pyramid_construction_...

Utilizing scanning electron microscopy, they discovered mineral compounds and air bubbles in samples of the limestone pyramid blocks that do not occur in natural limestone.

This may be a stupid question, but given the apparent interest and knowledge of concrete in the comments here, it seems like an appropriate time and place to ask:

Why can't they make coloured concrete?

Painting it doesn't seem to last/work. It is grey, always grey. Is there no way to apply colour to the mixture and retain its strength?

Seems it's possible - http://www.concretenetwork.com/concrete-color/charts.html - presumably it's either expensive or difficult to work with so it's not used often.

It's absolutely done, people just don't think of using concrete as a decorative finish as much.

I've seen red and blue and other colors. You can also stain and acid etch concrete for other texture treatments.

> It is grey, always grey.

Check out Decorative Concrete:

https://en.wikipedia.org/wiki/Decorative_concrete

https://www.pinterest.com/explore/decorative-concrete/

Bonus 1) Translucent Concrete:

https://en.wikipedia.org/wiki/Translucent_concrete

http://google.com/search?tbm=isch&gws_rd=cr&q=translucent+co...

Bonus 2) White Concrete, using Titanium Dioxide admixture, also cleans itself and its environment:

http://google.com/search?tbm=isch&gws_rd=cr&q=concrete+tio2

Bonus 3) Nanomaterials add a lot of new potential for strength, possibly color, as well as completely new applications. For instance, carbon nanotubes make concrete slightly electrically conductive, which makes it possible to do easy integrity testing, visible from low voltage current fluctuations near stresses, strains, cracks, etc. I wish I had more info on a prospective range of applications here.

Aside A) Clays (of possibly many colors) can also provide an even cheaper, more readily available, and similarly strong building material. Sindhi researchers pre-stressed and baked some test beams, and they were just about as strong as comparable concrete. See Emergence of New Era for Reinforced Baked Clay Construction (Memon, Bhatti, & Ansari): http://www.quest.edu.pk/rjournals/julydec2013/julydec2013_1.... I sincerely wonder how this ongoing wealth of research on concrete plus many generations old, likely undocumented, skill we have with clay construction could come together.

Here's the PNAS article that they don't link to in the article for some reason: http://www.pnas.org/content/early/2016/02/04/1520487113.abst...

Thanks for the link, but it is in the article. On news.mit.edu articles, when they do include links to papers, the links are presented in the "RELATED" list on the right side. They don't always remember to give links to papers, but they are better about it than the press/news sites of most universities.

This is great! Basically cement is a fractal substance. Are there other known fractal substances?

http://www.ncbi.nlm.nih.gov/pubmed/2577851 from 1988 starts:

> In recent years it has been shown that the structures of a wide variety of colloidal aggregates can be described in terms of the concepts of fractal geometry. The purpose of this review is to discuss some of the evidence for fractal geometry in experimental systems and indicate how fractal geometry can be used to develop a better understanding of their aggregation kinetics and physical properties.

so I think the answer is "many". Try https://scholar.google.com/scholar?q=fractal+material for some pointers.

Thank you so much for the pointers. So fascinating!

Google Scholar is a great resource for these sorts of research-oriented questions. I hope you continue to find it useful.

In case you are not already excited by discoveries in concrete, this should help: https://gimletmedia.com/episode/3-concrete/

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