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New Coating Helps Concrete Self-Heal

Monday, February 25, 2013

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The world’s first self-healing protective coating for cracks in concrete is the promise of new research and development by a team of Korean scientists.

“Sunlight-Induced Self-Healing of a Microcapsule-Type Protective Coating,” published Feb. 1 in ACS Applied Materials & Interfaces, describes the groundbreaking work by Chan-Moon Chung and colleagues at Yonsei University and Korea Conformity Laboratory in Korea.

Keeping Tiny Cracks Tiny

Researchers say the material is inexpensive, environmentally friendly, and holds the ability to self-repair damage to the world’s most widely used building material.

WSDOT

Washington State DOT says these cracks in the Aurora Bridge were cosmetic. The new coating aims to repair superficial cracks before they become more serious.

The idea is to prevent the spread of tiny cracks in concrete roads, bridges and other structures—an elusive goal that the scientists say “has been a major technological challenge.”

“Cracks allow water, salt used for deicing, and air to enter the concrete,” the American Chemical Society reports in a release about the project. “During winter weather, water in the cracks freezes, expands and the cracks get bigger, with road salt speeding concrete’s deterioration.”

A First for Concrete

A number of self-healing anticorrosive coatings for metal substrates are in development; NEI Corp. and a group of Dutch researchers have both unveiled such research over the last year.

However, “there have been no reports on self-healing protective coating for concrete,” says the Korean team.

The research was supported by Korean government science agencies and the National Research Foundation of Korea.

How it Works

The spray-applied, hydrophobic coating contains microcapsules loaded with a urea-formaldehyde polymer material that seals cracks. The act of cracking actually ruptures the microcapsules, releasing the healing agent, the journal says.

ACS

The coating is spray-applied to concrete surfaces. When a crack occurs in the substrate, the event ruptures the coatings's microcapsules, which release a healing agent that is solidified by sunlight.

Sunlight shining on the concrete activates and solidifies the sealant. Optical microscopy and scanning electron microscopy (SEM) confirmed the release and the filling response of the healing agent when applied to the surface of cellulose fiber-reinforced cement board or mortar.

“Our self-healing coating is the first example of capsule-type photo-induced self-healing system, and offers the advantages of catalyst-free, environment-friendly, inexpensive, practical healing,” the researchers’ report says.

Comment from chris atkins, (2/25/2013, 3:47 AM)

‘sunlight shines on the coating’ - not if the concrete is under the deck. Also its sometimes handy to know concrete is cracking, eg if a big lump is about to fall off or the structure is failing. All the best Chris

Comment from Tom Schwerdt, (2/25/2013, 8:26 AM)

Interesting, though after going through the published paper, the usual concerns about "self-healing" coatings apply: 1) The crack size tested was small, 4 mils across. 2) Usually the active lifespan of these micro-encapsulated crack-fillers is fairly short - ballpark a year, depending on conditions. (not discussed explicitly in the article) 3) Are we doing anything which wouldn't already be covered by an elastomeric acrylic? Chris' points are also well taken - lots of structural concrete never sees (much) sunlight. Chloride intrusion is a relatively big concern under open/leaky bridge deck joints in road-salting areas. However, these caps and beam ends rarely see any significant sunlight. One really nice thing about this paper is that in addition to the usual razor-blade test, they did some actual cracking of coated concrete, instead of just assuming that cutting through the coating with a razor blade is the same as cracking.