DailyDirt: Long-Lasting Concrete Ideas

from the urls-we-dig-up dept

Wed, Jul 16th 2014 5:00pm — Michael Ho

Every year, people pour billions of tons of concrete to build the stuff we live in and drive on. Concrete is everywhere, so it'd be nice to find better ways to make it and to make it more durable and to last longer. (FYI: Concrete is usually made up of 10-15% cement, and the cement is used to bind together sand and/or crushed rocks in concrete.) Here are just a few links on making better concrete.

Superhydrophobic Engineered Cementitious Composite (SECC) is a mouthful of a name for a flexible, super-strong and long-lasting building material that could enable bridges and roadways to last over a century with minimal maintenance. Roads made with conventional reinforced concrete generally need to be replaced or significantly repaired within a few decades. [url]
Certain bacteria can produce limestone, and adding these bugs to concrete makes a living building material that can repair itself. The trick is keeping the bacteria dormant (and not dead) until they're needed to help fill in small cracks in the concrete. [url]
Roman concrete has lasted for thousands of years and is far superior to Portland cement in places like marine harbors. The lost recipe for Roman concrete probably contains lime and volcanic rock or volcanic ash, and modern concrete/cement could benefit from examining ancient samples of durable Roman building materials. [url]

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Filed Under: cement, concrete, materials, portland cement, roman concrete, secc, self-healing, superhydrophobic engineered cementitious composite

9 Comments

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Mason Wheeler (profile), 16 Jul 2014 @ 5:06pm

Superhydrophobic concrete would very likely make a horrible material for roadways, because hydrophobic materials tend to have one other thing in common: low friction. Which doesn't sound so bad until you realize that in the context of vehicles and roads, friction is more commonly known as traction, and surfaces that don't have much of it are called "slippery" in layman's terms.
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Anonymous Coward, 16 Jul 2014 @ 5:10pm

Re:
The idea is to use it for structural elements, not necessarily the traction surface.
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Anonymous Coward, 16 Jul 2014 @ 5:16pm

I recall hearing about Roman cement using animal fat and blood as surfactants. It ended up getting abandoned later on as pagan nonsense, which is pretty understandable actually. Since it does sound like superstitious sacrifices.
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Anonymous Coward, 16 Jul 2014 @ 5:18pm

Properly cured concrete will last a long long time. However, these days, due to cost constraints, etc, curing your concrete is the first thing to go out the window.
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alternatives(), 16 Jul 2014 @ 6:22pm

roman concrete
"lost"? Posted the link to this more than once here on techdirt.

http://www.romanconcrete.com/orderbook.htm

And then you have the idea the grand Egyptian pyramids are just poured rock.

http://www.geopolymer.org/archaeology/pyramids/pyramids-3-the-formula-the-invention-of-stone
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art guerrilla (profile), 17 Jul 2014 @ 5:25am

Re:
w-e-l-l, the actual chemical process (called hydration), theoretically goes on forever (albeit in an asymptotic curve), as long as it has some water to do the reaction...
but what you say is true: depending on the environment, concrete can be strengthened by proper 'curing' (so to speak), as far as keeping it moist over the first week or so...
the other major problem, is that ignorant mud pushers mix in *way* too much water because it makes it easier to "pour" (concrete should always be "placed", not "poured", says my old concrete structures prof) and slop around the concrete, but causes weaker concrete in several ways: tends to segregate the aggregate, and makes the cement itself weaker...
been all kinds of admixtures for a long time for specialized mixes: retardants to slow the reaction, accelerants (stop flagging real words, you useless spel czech) for quick-setting, fiberglass threads for strength and to increase its resistance to cracking, etc...
oh, concrete WILL crack, just a matter of controlling it where you want it to crack...
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Michael Ho (profile), 17 Jul 2014 @ 11:31am

Re: roman concrete
I saw one of your previous comments:
https://www.techdirt.com/articles/20100418/2354599066/dailydirt-egyptian-pyramid-construction-techni ques.shtml#c10

Is there ancient scroll that actually describes how Roman concrete is made? I know there are some descriptions of some of the ingredients, but the whole process...?
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Robert, 17 Jul 2014 @ 11:37am

Re: Re:
" not "poured", says my old concrete structures prof"

Very true. Also the time between mix and pour, temp, humidity....

I happened to go to a high school that had all sorts of testing equipment for my "Strength of Materials" course. Believe me when I say proper curing is extremely important to the strength and longevity of concrete. My concrete biscuits proved the point.

Romans used fly ash which created a stronger, less porous cement.
http://www2.buildinggreen.com/article/using-fly-ash-concrete-0
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Anonymous Coward, 17 Jul 2014 @ 11:57am

Re: Re: roman concrete
I saw something on the History Channel the other night (coincidentally, I was reading this page as it happened :D) that compared the strength of ancient vs. modern concrete and visited the likeliest source of their volcanic material in Italy. It also suggested an ancient text from a library still available today revealed the process, but I can't recall whether it went into detail on that matter or not (bad selective memory, bad!).
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