self healing concrete

Self-healing Concrete for Safer, More Durable Infrastructure Science Daily (04/24/09)

University of Michigan researchers have developed a new self-healing concrete that can repair its own cracks without human intervention, using only naturally occurring water and carbon dioxide. A few rainy days could mend a damaged bridge using this kind of concrete, called Engineered Cement Composite (ECC), which is made to bend and crack in narrow hairlines. "We've created a material with such tiny crack widths that it takes care of the healing by itself. Even if you overload it, the cracks stay small," said Victor Li, the E. Benjamin Wylie Collegiate Professor of Civil Engineering and a professor of Materials Science and Engineering. Li's researchers found that self-healed specimens were able to get back most or all of their original strength after being subjected to a 3 percent tensile strain, enough to cause catastrophic breakage in traditional concrete. "We found, to our happy surprise, that when we load it again after it heals, it behaves just like new, with practically the same stiffness and strength," Li said. The research team has been working for 15 years to develop ECC, which is flexible and studded with reinforcing fibers that make it behave more like a metal than a traditional concrete. The research has been published online in the journal Cement and Concrete Research and will also appear in a forthcoming print edition.

(http://www.sciencedaily.com/releases/2009/04/090422175336.htm)

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Supe said:

I can't even imagine all the manhours that stuff would have saved us. 21.6% of ALL NCR's issued on our sites for 2008 were concrete related, and almost all of them were from foundation cracks.

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MA_PE said:

I'm not sure I understand what this is doing. Concrete strength is in compression not tension. healing of cracks is to prevent detrimental loss of proctective concrete coating over the tensile reinforcement. How can it "get its strength back?"
You don't design unreinforced concrete for a tensile application.

How does this differ from typical autogenous healing?

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MA_PE said:

foundation cracks from loading or shrinkage?

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TXengrChickPE said:

If you read the whole article, it sounds like it's not intended to be used the same way traditional concrete is used. It sounds like it's concrete that acts like steel... so reinforcing would not be needed... in traditional concrete, cracks lead to corrosion of the reinforcement... with this stuff, the cracks heal themselves, AND it has it's own tensile strength, so the steel isn't even needed.
Pretty cool if it's cost effective.

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More flexible than traditional concrete, ECC acts more like metal than glass. Traditional concrete is considered a ceramic. Brittle and rigid, it can suffer catastrophic failure when strained in an earthquake or by routine overuse, Li said. But flexible ECC bends without breaking. It is studded with specially-coated reinforcing fibers that hold it together. ECC remains intact and safe to use at tensile strains up to 5 percent. Traditional concrete fractures and can’t carry a load at .01 percent tensile strain.

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Today, builders reinforce concrete structures with steel bars to keep cracks as small as possible. But they’re not small enough to heal, so water and deicing salts can penetrate to the steel, causing corrosion that further weakens the structure. Li’s self-healing concrete needs no steel reinforcement to keep crack width tight, so it eliminates corrosion.

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