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Grad student may have discovered economically feasable smart concrete

Most people think of driveways and sidewalks when concrete is mentioned. Concrete is also used as a structural building material in many large buildings around the country. The problem with concrete as a building material is that as it develops cracks, the material becomes weaker.

Researchers are currently investigating ways to make smart materials that can heal themselves from cracks and other minor imperfections as a way to prolong the life of the material and increase its strength. A grad student named Michelle Pelletier from the University of Rhode island has made a discovery that may one day lead to smart materials that are cost effective to produce and easy to use.

Pelletier is a master's degree candidate and has developed a method of embedding microencapsulated sodium silicate healing agents directly into concrete. The idea is that the tiny microcapsules, which hold the sodium silicate agent that reacts with calcium hydroxide naturally in concrete, will rupture when cracks form and release the repairing agent.

When the sodium silicate inside the microcapsules reacts with the calcium hydroxide in the concrete a chemical reaction causes a gel-like material to form that can fill cracks and pores in the area of the crack and hardens in about a week.

"Smart materials usually have an environmental trigger that causes the healing to occur," explained Pelletier, who is collaborating on the project with URI Chemical Engineering Professor Arijit Bose. "What's special about our material is that it can have a localized and targeted release of the healing agent only in the areas that really need it."

Tests of the self-healing concrete have shown that when stressed to near breaking the concrete with the microencapsulated sodium silicate is able to regain up to 26% of its original strength. Standard concrete when stressed to similar levels only regains 10% of its strength. Improvements in the

Another potential benefit of the new self-healing concrete being studied is if by immediately filling cracks in the concrete, water can be prevented from reaching the steel reinforcement bars that are used to add strength to concrete. Water getting to the steel reinforcement bars causes the bars to rust leading to reduced strength.

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RE: thoughts...
By MozeeToby on 5/25/2010 1:54:45 PM , Rating: 2
I don't think anyone is saying that this would replace concrete everywhere and for everything but there are some situations where the extra time and expense might be worth it. In Milwaukee Wisconsin for instance, they have to go around a couple times a year and knock all the loose concrete off the overpasses and bridges (so it doesn't fall and kill someone). Once enough concrete is gone or damaged salt water (from snow melt in the winter) gets to the rebar and rusts it out very quickly.

The end result is unsafe bridges that need to be replaced more often than the engineers would have ever expected. Even if all it does is keep water away from the rebar, you've got a winner right there for some applications (although, why don't they just coat the rebar in plastic?).

RE: thoughts...
By michael67 on 5/26/2010 3:24:15 AM , Rating: 3
(although, why don't they just coat the rebar in plastic?).

That would take away the hole purpose of the rebar, as it has to be one whit concrete.

Do galvanized rebars are used in places ware the outside environment could reach's the rebars, but at almost $0.5~1 per kg steel, it costing a lot, and a little less strong then whit out

You will also see that they never use real new rebars, but always rusted ones, for two reasons, 1 to remove the carbon skin from the steel, 2 make the surface more rough, for a better bond whit the concrete.

RE: thoughts...
By pattycake0147 on 5/29/2010 7:41:20 PM , Rating: 2
Some re-bar is coated in epoxy. It is very common to see this put in safety conscious applications such as bridges.

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