Concrete isn't thought of as a plastic, but plasticity at small scales boosts concrete's utility as the world's most-used material by letting it constantly adjust to stress, decades and sometimes even centuries after hardening. Rice University researchers are a step closer to understanding why.
The Rice lab of materials scientist Rouzbeh Shahsavari performed an atom-level computer analysis of tobermorite, a naturally occurring crystalline analog to the calcium-silicate-hydrate (C-S-H) that makes up cement, which in turn holds concrete together. By understanding the internal structure of tobermorite, they hope to make concrete stronger, tougher and better able to deform without cracking under stress.
Their results appear this week in the American Chemical Society journal ACS Applied Materials and Interfaces .
Tobermorite, a key element in the superior concrete Romans used in ancient times, forms in layers, like paper stacks that solidify into particles. These particles often have screw dislocations, shear defects that help relieve stress by allowing the layers to slide past each other. Alternately, they can allow the layers to slip only a little before the jagged defects lock them into place.
The researchers built the first computer models of tobermorite "super cells" with dislocations either perpendicular to or in parallel with layers in the material, and then applied shear force. They found that defect-free tobermorite deformed easily as water molecules caught between layers helped them glide past each other.
But in particles with screw defects, the layers only glided so far before being locked into place by the tooth-like core dislocations. That effectively passed the buck to the next layer, which glided until caught, and so on, relieving the stress without cracking.
-- submitted from IRC
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Rice University scientists have developed micron-sized calcium silicate spheres that could lead to stronger and greener concrete, the world's most-used synthetic material.
To Rice materials scientist Rouzbeh Shahsavari and graduate student Sung Hoon Hwang, the spheres represent building blocks that can be made at low cost and promise to mitigate the energy-intensive techniques now used to make cement, the most common binder in concrete.
The researchers formed the spheres in a solution around nanoscale seeds of a common detergent-like surfactant. The spheres can be prompted to self-assemble into solids that are stronger, harder, more elastic and more durable than ubiquitous Portland cement.
[...] The work builds on a 2017 project [DOI: 10.1021/acsami.7b12532] [DX] by Shahsavari and Hwang to develop self-healing materials with porous, microscopic calcium silicate spheres. The new material is not porous, as a solid calcium silicate shell surrounds the surfactant seed.
Size- and Shape-Controlled Synthesis of Calcium Silicate Particles Enables Self-Assembly and Enhanced Mechanical and Durability Properties (DOI: 10.1021/acs.langmuir.8b00917) (DX)
Related: Biologists Create Self-Healing Concrete
Probing Ways to Turn Cement's Weakness to Strength
Roman Concrete Explained
The Rock Solid History of Concrete
Fungi Can Help Concrete Heal Its Own Cracks
(Score: 3, Interesting) by Runaway1956 on Thursday January 05 2017, @01:55AM
The Romans poured concrete that still exists today. What's more, they poured concred sea breaks that are still in place today. Concrete, in sea water. That's just about the harshest environment on earth, and their concrete still exists.
And, we have fly-by-night companies in the US whose concrete doesn't last twenty years.
We need to figure out how to pour Roman concrete, and use it on our highways. If these guys can figure out how to do it, I'm all for them. Imagine - pour any of our interstates of concrete, and there is only very minor patching to be done for the next fifty, or even hundred years. As things stand, very little of our highway system lasts 20 years without major rework.
That is a HUGE energy expenditure, not to mention economic cost.
(Score: 1, Interesting) by Anonymous Coward on Thursday January 05 2017, @02:26AM
We can and do make the same stuff today. It is just a mater of cost. It has more to do with the 'cement' part.
https://en.wikipedia.org/wiki/Portland_cement [wikipedia.org]
https://en.wikipedia.org/wiki/Roman_concrete [wikipedia.org]
As the usage of coal changes you may see a shift back to the other type. Again due to cost.
(Score: 3, Insightful) by driverless on Thursday January 05 2017, @02:33AM
Beat me to it. You can make near-indestructible concrete if you don't care what it costs. Near where I live there are long-buried Victorian seawalls that are an absolute bastard to remove because they didn't know the correct ratios to use in the mix at the time they were built and so overdid things a wee bit, with the result that you can't just go in with a jackhammer and break it up, it requires a ridiculous amount of effort. Modern concretes, now that we know the chemistry and physics, are a fine balancing act, the minimum amount of expensive components needed to still have it hold together and up to spec. That's why you get crap concrete, the contractors saved money by reducing the quantity of the more expensive components in the mix.
(Score: 2) by fishybell on Thursday January 05 2017, @03:12AM
A major source of concrete problems today are also a result of the iron reinforcement. The rebar expands as it rusts/corrodes, breaking the concrete from the inside.
(Score: 2) by Runaway1956 on Thursday January 05 2017, @03:23AM
Interesting. Do you have citations for that? In my experience, it seems that rebar doesn't rust or corrode until/unless the concrete is first damaged, allowing moisture and oxygen to get to the rebar. I don't recall ever removing undamaged concrete, to find rusted rebar inside. Then again, maybe I wasn't really watching for rusted rebar. In cases where the concrete is badly cracked, flaked, and chipped, I've often seen rusted rebar extending down into the undamaged concrete. Are there studies on this, or are you, like me, basing your conclusion on personal experience?
I will note, in support of your claim, that the state of Texas often specifies vinyl clad reinforcement bar in their structures. The first time I used vinyl clad was in the New Boston bridge over the Red River. There is no naked iron in that structure, everything is heavily coated, most of it in vinyl.
(Score: 4, Interesting) by JoeMerchant on Thursday January 05 2017, @04:05AM
https://en.wikipedia.org/wiki/Spall [wikipedia.org]
http://www.hdb.gov.sg/cs/infoweb/residential/living-in-an-hdb-flat/home-maintenance/spalling-concrete [hdb.gov.sg]
https://failures.wikispaces.com/Concrete+Bridge+Failures+-+Deterioration+and+Spalling [wikispaces.com]
https://www.concretenetwork.com/fix-spalled-concrete/ [concretenetwork.com]
http://www.truesdellcorp.com/index.php/services/articles/41-general/429-corrosion-protection-and-repair-of-reinforced-concrete [truesdellcorp.com]
it's a big enough problem to have extensive study, publication, and service providers who specialize in maintenance to prevent it, and repair work after it starts.
🌻🌻 [google.com]
(Score: 2) by Runaway1956 on Thursday January 05 2017, @10:40PM
Thank you, Joe, great job!
(Score: 0) by Anonymous Coward on Thursday January 05 2017, @04:49AM
Two words: Road salt
(Score: 3, Touché) by JoeMerchant on Thursday January 05 2017, @04:01AM
The Romans hadn't perfected free market economics: contract awarding to the lowest bidder, planned obsolescence, limited warranties and bankruptcy protection.
Many of the problems in modern "things" are short-path traceable to the economic system that builds them.
🌻🌻 [google.com]
(Score: 2, Touché) by khallow on Thursday January 05 2017, @04:54AM
(Score: 3, Funny) by driverless on Thursday January 05 2017, @02:27AM
The Rice lab of materials scientist Rouzbeh Shahsavari performed an atom-level computer analysis of tobermorite
Future research will focus on orinocite, tomskite, aldernite, and greatunclebulgarite.
(Score: 0) by Anonymous Coward on Thursday January 05 2017, @09:28AM
amirite?