Roman concrete threads may not be made of Roman concrete, but they do ok:<p><a href="https://hn.algolia.com/?dateRange=all&page=0&prefix=true&query=roman%20concrete&sort=byDate&type=story" rel="nofollow">https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...</a><p>Last year: <a href="https://news.ycombinator.com/item?id=20482050" rel="nofollow">https://news.ycombinator.com/item?id=20482050</a><p>2017: <a href="https://news.ycombinator.com/item?id=14690329" rel="nofollow">https://news.ycombinator.com/item?id=14690329</a><p>2013: <a href="https://news.ycombinator.com/item?id=5883443" rel="nofollow">https://news.ycombinator.com/item?id=5883443</a><p>2010: <a href="https://news.ycombinator.com/item?id=1852000" rel="nofollow">https://news.ycombinator.com/item?id=1852000</a>
It is always a bit annoying to read an article based on the work of someone specialized in one area that talks down specialists in another area.<p>Is is definitely interesting to read about some unexpected properties that ancient concrete with volcanic ash as one of its ingredients has. For modern cement there is a different set of choices for binding materials, were you can choose the ingredients that are locally good available.<p>Also there are definitely mistakes that get made in modern construction.
- Maybe the structure has enough rebar to handle the forces that act on the structure, but not enough to prevent the small cracks that hurt durability (although that is something that should be checked).
- Maybe the detailing of the rebar is not correct. Lapping lengths are too short. Often I see that the workers who put in the rebar come up with creative solutions but understanding why it now doesn't work well is outside their expertise.
- Maybe the concrete layer that protects the rebar (covering) from rusting is to thin or to porous. The amount of covering required depends on the exposure classification. And the concrete mixture influrences how porous the concrete becomes over the years.<p>For modern engineering you specify the exposure classes that a structure falls in. Carbonatation (<a href="https://en.wikipedia.org/wiki/Carbonatation" rel="nofollow">https://en.wikipedia.org/wiki/Carbonatation</a>), a reaction where calcium in the concrete with CO2 in the air, which changes the acidity in the concrete. Chlorids, from sources such as seawater or de-icing salts, also impact the acidity of the concrete. Chemical acids, basically everything biological such as milk, beer, manure, and other acids dissolve the calcium. And frost can cause parts of the concrete to flak off. All those effects can get worse if the concrete gets porous. But all are well understood problems that inform the necessary mixture.
A material science professor at TU Delft [1] and this material is commercially available [2].<p>From the abstract of `Bacteria-Based Self-Healing Cementitious Composite for Application in Low-Temperature Marine Environments` [3]: "The composite displayed an excellent crack-healing capacity, reducing the permeability of cracks 0.4 mm wide by 95%, and cracks 0.6 mm wide by 93% following 56 days of submersion in artificial seawater at 8 ◦C. Healing of the cracks was attributed to autogenous precipitation, autonomous bead swelling, magnesium-based mineral precipitation, and bacteria-induced calcium-based mineral precipitation in and on the surface of the bacteria-based beads. "<p>[1] <a href="https://www.tudelft.nl/citg/over-faculteit/afdelingen/materials-mechanics-management-design-3md/sections-labs/materials-environment/staff/dr-hm-henk-jonkers/" rel="nofollow">https://www.tudelft.nl/citg/over-faculteit/afdelingen/materi...</a><p>[2] <a href="https://www.basiliskconcrete.com/hoe-werkt-het/?lang=en" rel="nofollow">https://www.basiliskconcrete.com/hoe-werkt-het/?lang=en</a><p>[3] doi:10.3390/biomimetics2030013
> <i>We may think we're at the height of human knowledge, but the ancients did possess precious knowledge that has been lost to time.</i><p>I would love to hear why a chemical analysis doesn't solve the riddle here. Scientists were able to isolate a strain of the coronavirus and publish the entire genetic sequence in a matter of days, but we can't analyze a sample of concrete?
Is this subject to survivorship bias? Will future generations wonder at the inexplicable durability of a few modern structures still available to wonder at, for accidental reasons?
Some prior discussion on this at <a href="https://news.ycombinator.com/item?id=20482050" rel="nofollow">https://news.ycombinator.com/item?id=20482050</a><p>The top comment there links to two other discussions.
This is amazing - I wonder if some luck was involved. I’m sure they were deliberately trying to make strong/lasting concrete but they couldn’t have tested it over hundreds of years, let alone 1000s. Is there a degree of chance to it being this effective?
All concrete gets stronger over time!
<a href="https://www.concrete.org/tools/frequentlyaskedquestions.aspx?faqid=13" rel="nofollow">https://www.concrete.org/tools/frequentlyaskedquestions.aspx...</a>
edit: [adding more detail, removing all caps]
Contracts will often specify a 7day or 28day strength because the concrete will keep getting stronger over time. Separate cylinders are poured for independent testing of the strength<p>Here’s a good textbook on concrete:
Concrete: Microstructure, Properties, and Materials
Textbook by Paulo J. M. Monteiro and Povindar Kumar Mehta
Another interesting piece of lost ancient knowledge:<p><a href="https://en.wikipedia.org/wiki/Greek_fire" rel="nofollow">https://en.wikipedia.org/wiki/Greek_fire</a>
Our modern building practices and materials are not optimized for longevity. What incentive in modern times does a contractor have in building homes that last hundreds of years?<p>The average person is too ignorant to know or care anyway.