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Researchers Make Bendable Concrete
karvind writes "PhysOrg is reporting that scientists from University of Michigan have developed a new type of fiber-reinforced bendable concrete. The new concrete looks like regular concrete, but is 500 times more resistant to cracking and 40 percent lighter in weight. Tiny fibers that comprise about 2 percent of the mixture's volume partly account for its performance. Also, the materials in the concrete itself are designed for maximum flexibility. Because of its long life, the Engineered Cement Composites (ECC) are expected to cost less in the long run, as well." Michigan roads must make the perfect test cases for this stuff, and I look forward to their improvement.
Why not link to the source at the U of M News Service:
U-M researchers make bendable concrete
Technocrat.net had this article earlier today, and without the extra advertising.
interesting stuff!
There is also translucent concrete which works by having optical fibers mixed in.
No, the only reason asbestos is damaging to lungs is that it
tends to form particles 0.5 to 1.4 microns in diameter, which is the range in which any paticulate matter is lung damaging and carcinogenic in nature. Asbestos is not mutagenic; any particles that form mainly in that size will cause lung cancer. It is a strange twist of fate that asbestos fibers disintigrate to particles that size, but it has nothing to do with fibers in general or their chemistry.
There's an alternative they're trying out in certain areas of Wisconsin. It's basically asphalt, but with a very high rubber content. They grind old tires into the asphalt. The net result is that it costs about the same to lay, and it can "heal" itself to some degree. The main concern is how safe it is when completely frozen, which is why it's only being tested in certain sections of freeway.
If it does prove to be a viable material to replace basic asphalt, it'll be great for Wisconsin drivers... we deal with slippery roads all winter then road construction in the spring, summer, and fall. If this can at least eliminate pothole patching, it'll pay for itself many times over.
You have enemies? Good. That means you've stood up for something, sometime in your life. --Winston Churchill
"Tiny fibers that comprise about 2 percent of the mixture's volume partly account for its performance."
The fibers are only one part of the improvement. The article also mentions replacing other major components in the concrete, including the bulk aggregate. Presumably the new components are also lighter and would account for the 40% reduction.
The increased strength makes it possible to use less of it to build structures of similar strength. You need 40% less of the fiber concrete to get the same strength as the traditional concrete.
You're misinterpreting the Popular Mechanics article. These are not deep submersibles. The advantage of a concrete submarine, like the advantage of a WWII Liberty ship, is that it is cheap. That's it. Cheap. It doesn't perform better, it doesn't last longer, and if you're a civil engineer, you'd probably laugh at the idea of crawling into one and diving into the deeper depths of the ocean.
_ HOV/new_hov_brochure.pdf (PDF link).
The WWII Liberty ship had a design life of 5 years and a "positive" ROI if it managed to survive its first (outbound) trip to deliver cargo to Europe. The entire vessel could be completed in an average of roughly 60 days. You could build them quickly using forms, you could build a lot of them using cheap materials, and they couldn't be sunk quickly enough to cut off the British from the American industrial complex. Now imagine the concrete submarine. Same principle, different wartime purpose.
Now the nerdly part. From a materials perspective, you're dead wrong.
To start with, the nit: Concrete has practically no tensile strength in comparison to steel - reinforced concrete design assumes that all tensile strength is provided by the embedded steel rebar.
Next, the myth: Concrete has good compressive strength - high strength varieties can have crush pressures exceeding 140 megapascals. Steel has much better compressive strength - high strength varieties can have crush pressures exceeding 2500 megapascals. Steel is stronger, but vastly more expensive. Concrete is weaker, but, literally, dirt cheap. Reinforced concrete is a practical compromise that optimizes economy versus loads for a particular design envelope (notice that modern skyscrapers do not have loads of reinforced concrete incorporated into their design).
Next, the mechanical nit: unless you've designed a perfect sphere, your concrete submarine will not only have to resist compression. Various parts of the structure will experience "tension" in response to bending moments and shear forces that resist the spreading tendency that will occur in a non-spherical, hollow form subjected to a pressure differential (tension is in quotes because I'm referring to subelements that are being pulled apart, not to the entire cross section as is normally the case). You can mitigate this problem by using pre-stressed concrete, so that the entire structure is under compression, but you will have spent a portion of your compression resistance to eliminate that problem. Steel makes your life much, much easier.
Finally, the materials problem: Concrete is porous and breaks down in marine environments as the salts attack the calcium hydroxide matrix, dissolving the cohesive minerals, depositing non-cohesive minerals, and splitting the crystalline structure like ice and the Old Man of the Mountain. Concrete is used in marine environments, but it deteriorates comparatively quickly. Now cycle your concrete though tens or hundreds of atmospheres of pressure in a marine environment. Your concrete will deteriorate even more quickly. Coatings will help, but they will have to be inspected frequently because of the frequent depressurization.
In conclusion, it would be a bad idea. The depth limitations of current deep submersibles are not caused by the pressure hull, but instead by more practical considerations like transport and life support. See http://www.unols.org/committees/dessc/replacement