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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 Bruneauinfo on 5/25/2010 4:51:33 PM , Rating: 3
i disagree with point 2 and 3. concrete is overdesigned to deal with the fact it cracks and tends to fail over time. having this additive that repairs it as it fails could mean longer design life with lower initial strength requirements - a less expensive mix design due to a lower cement requirement.

to the third point, at least two major considerations are taken when designing concrete - the cost of the concrete and the life of the concrete. a mix design may cost more up front, but if it lasts longer due to the fact it heals itself the product has a longer lifespan and longer periods between repairs.

and as for the issues of reinforcing steel and cracks - especially in concrete exposed to the elements - water getting in cracked concrete causes at least two types of deterioration - the water and air getting through the crack causes the steel to rust faster (rusting steel expands so figure out what happens to the crack), and in freezing temperatures in the winter the water freezes and causes freeze thaw deterioration. so even if the self-healing attribute of this additive gave a minimal return on strength, keeping the water out of the cracked concrete would mean longer life for the product.

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