The Industrial Key to a Safer Life
In 2008, one quarter of the bridges in the United States were structurally unsound or functionally obsolete, most likely due to delayed maintenance of bridges and extreme underfunding for maintenance (Forbes). After the American Society of Civil Engineering (ASCE) graded the U.S. infrastructure a “D”, the ASCE estimated that in order to bring that grade up to a “B,” we needed a budget of about 2.2 trillion dollars. However, a new technology suggests an easier and cheaper way to fix concrete structures before water can maneuver it’s way to the steel substructure.
Researchers at University of Cardiff, the University of Bath, and the University of Cambridge believe that the answer to the instability of concrete structures around the world lies in a new scientific development commonly referred to as self-healing concrete. Self-healing concrete will tackle the durability issues of concrete and reduce maintenance costs.
Concrete is a composite material because it is composed of ceramics and metals. Concrete is mainly composed of lime (calcium oxide), a stone called aggregate, and sand. Although concrete is cheap to produce and can withstand large amounts of weight, it is also very brittle and has low tensile strength, which is the maximum stress a material can withstand while being pulled or stretched before breaking. To strengthen concrete structures, engineers reinforce the structures with steel. However, when concrete cracks, even minimally, water enters the cracks and will eventually maneuver towards the steel reinforcements. The water causes the steel to rust, which makes the structure instable.
However, in self-healing concrete, bacteria held in microcapsules would be added to the concrete mixture. These microcapsules would hold the bacteria, the nutrients the bacterium needs to survive, and calcium lactate. When self-healing concrete cracks and water and oxygen seep into the concrete, the bacteria are released from the microcapsules. The bacteria then react with the oxygen, water, and calcium lactate that was released from the microcapsule, creating lime, the main component of concrete, which then fills the cracks in the concrete. In addition to the bacteria healing the crack in the concrete, the bacteria also uses oxygen in the reaction, further preventing corrosion of the steel reinforcements.
Although the idea of this product is very promising, scientists are still perfecting the self-healing concrete, which is not ready for industrial use yet. Researchers are struggling to keep the bacteria alive for a long period of time because, as Dr. Richard Cooper of the Biology and Biochemistry at Bath University, who is researching the self-healing concrete, said, the "Cement is highly alkaline, making it a hostile environment for bacteria. We'll be assessing different species of bacteria to find one that is able to form abundant spores and which will survive and germinate in this environment.”
However, Dr. Chan-Moon Chung of Yonsei University in South Korea proposed a solution to the problem of the short-lived bacteria. Dr. Chung’s idea leans away from the biological approach and focuses more heavily on the chemical aspect of self-healing concrete. Dr. Chung and his peers have observed that when methacryloxypropyl-terminated polydimethylsiloxane and benzoin isobutyl ether are combined and exposed to sunlight, they create a waterproof polymer that sticks to concrete, providing a complete barrier against weather (The Economist). Chung and his team propose that the two chemicals be stored in microcapsules strong enough to hold the chemicals, but weak enough to break with the concrete around it. Then, when concrete cracks, the microcapsules surrounding the crack break open, releasing the chemicals to fill the crack, cling to the concrete, and solidify in the exposure to sunlight.
Although this technology is still in developmental stages, it is already showing promising results. Researchers of Delft Technical University in the Netherlands tested the biological self-healing concrete, which repaired its own cracks of up to 0.5 mm wide (Smart Planet). Dr. Chung has also performed tests on his chemical self-healing concrete by mixing the microcapsules containing the chemicals with a liquid polymer and spraying this mixture onto the surface of multiple concrete blocks. Then, he applied significant amounts of pressure to each concrete block until they began to crack. Following this, Dr. Chung placed the concrete blocks in the sunlight, allowing the released chemicals to solidify. After being submerged in water for twenty-four hours, the blocks that had been treated with polymer containing microcapsules retained only 0.4 grams of water as compared to an untreated block of concrete, which absorbed 11.3 grams of water.
Even though these results are promising, Dr. Chung found that the healed concrete only remains waterproof for about one year. Dr. Chung hopes to extend this amount of time in the upcoming year. Researchers working on biological self-healing concrete, such as Dr. Richard Cooper, will continue to work on keeping the bacteria alive in their microcapsules for extended periods of time.
Sources
http://www.sciencedaily.com/releases/2012/04/120426105001.htm
http://www.smartplanet.com/blog/bulletin/self-healing-concrete-seals-its-own-cracks/
http://www.technologyreview.com/news/511911/self-healing-concrete-uses-sunlight-to-fix-its-own-cracks/
http://www.periodicvideos.com/videos/mv_concrete.htm
http://en.wikipedia.org/wiki/Properties_of_concrete
http://phys.org/news/2013-05-micro-capsules-bacteria-self-healing-concrete.html
http://www.technology4change.com/page.jsp?id=106
http://www.economist.com/blogs/babbage/2013/03/civil-engineering
http://www.engineeringtoolbox.com/concrete-properties-d_1223.html
Researchers at University of Cardiff, the University of Bath, and the University of Cambridge believe that the answer to the instability of concrete structures around the world lies in a new scientific development commonly referred to as self-healing concrete. Self-healing concrete will tackle the durability issues of concrete and reduce maintenance costs.
Concrete is a composite material because it is composed of ceramics and metals. Concrete is mainly composed of lime (calcium oxide), a stone called aggregate, and sand. Although concrete is cheap to produce and can withstand large amounts of weight, it is also very brittle and has low tensile strength, which is the maximum stress a material can withstand while being pulled or stretched before breaking. To strengthen concrete structures, engineers reinforce the structures with steel. However, when concrete cracks, even minimally, water enters the cracks and will eventually maneuver towards the steel reinforcements. The water causes the steel to rust, which makes the structure instable.
However, in self-healing concrete, bacteria held in microcapsules would be added to the concrete mixture. These microcapsules would hold the bacteria, the nutrients the bacterium needs to survive, and calcium lactate. When self-healing concrete cracks and water and oxygen seep into the concrete, the bacteria are released from the microcapsules. The bacteria then react with the oxygen, water, and calcium lactate that was released from the microcapsule, creating lime, the main component of concrete, which then fills the cracks in the concrete. In addition to the bacteria healing the crack in the concrete, the bacteria also uses oxygen in the reaction, further preventing corrosion of the steel reinforcements.
Although the idea of this product is very promising, scientists are still perfecting the self-healing concrete, which is not ready for industrial use yet. Researchers are struggling to keep the bacteria alive for a long period of time because, as Dr. Richard Cooper of the Biology and Biochemistry at Bath University, who is researching the self-healing concrete, said, the "Cement is highly alkaline, making it a hostile environment for bacteria. We'll be assessing different species of bacteria to find one that is able to form abundant spores and which will survive and germinate in this environment.”
However, Dr. Chan-Moon Chung of Yonsei University in South Korea proposed a solution to the problem of the short-lived bacteria. Dr. Chung’s idea leans away from the biological approach and focuses more heavily on the chemical aspect of self-healing concrete. Dr. Chung and his peers have observed that when methacryloxypropyl-terminated polydimethylsiloxane and benzoin isobutyl ether are combined and exposed to sunlight, they create a waterproof polymer that sticks to concrete, providing a complete barrier against weather (The Economist). Chung and his team propose that the two chemicals be stored in microcapsules strong enough to hold the chemicals, but weak enough to break with the concrete around it. Then, when concrete cracks, the microcapsules surrounding the crack break open, releasing the chemicals to fill the crack, cling to the concrete, and solidify in the exposure to sunlight.
Although this technology is still in developmental stages, it is already showing promising results. Researchers of Delft Technical University in the Netherlands tested the biological self-healing concrete, which repaired its own cracks of up to 0.5 mm wide (Smart Planet). Dr. Chung has also performed tests on his chemical self-healing concrete by mixing the microcapsules containing the chemicals with a liquid polymer and spraying this mixture onto the surface of multiple concrete blocks. Then, he applied significant amounts of pressure to each concrete block until they began to crack. Following this, Dr. Chung placed the concrete blocks in the sunlight, allowing the released chemicals to solidify. After being submerged in water for twenty-four hours, the blocks that had been treated with polymer containing microcapsules retained only 0.4 grams of water as compared to an untreated block of concrete, which absorbed 11.3 grams of water.
Even though these results are promising, Dr. Chung found that the healed concrete only remains waterproof for about one year. Dr. Chung hopes to extend this amount of time in the upcoming year. Researchers working on biological self-healing concrete, such as Dr. Richard Cooper, will continue to work on keeping the bacteria alive in their microcapsules for extended periods of time.
Sources
http://www.sciencedaily.com/releases/2012/04/120426105001.htm
http://www.smartplanet.com/blog/bulletin/self-healing-concrete-seals-its-own-cracks/
http://www.technologyreview.com/news/511911/self-healing-concrete-uses-sunlight-to-fix-its-own-cracks/
http://www.periodicvideos.com/videos/mv_concrete.htm
http://en.wikipedia.org/wiki/Properties_of_concrete
http://phys.org/news/2013-05-micro-capsules-bacteria-self-healing-concrete.html
http://www.technology4change.com/page.jsp?id=106
http://www.economist.com/blogs/babbage/2013/03/civil-engineering
http://www.engineeringtoolbox.com/concrete-properties-d_1223.html
Chemistry of Concrete Supplement
Concrete is a heterogeneous mixture of compounds such as lime and sand and ceramics such as aggregate. Concrete has covalent and ionic bonds because both ionic and covalent bonds hold together the molecules that compose concrete. For example, sand is a covalent bond because the two elements that compose sand, silicon and oxygen, are both nonmetals and can only be bonded covalently. However, the main component of concrete, lime (calcium oxide), is composed of one metal and one nonmetal, making it an ionically bonded molecule. Due to the fact that the lime encases and glues together the rest of the components of concrete, the ionic bonds are the most dominant bonds in concrete. Also, concrete is a composite, meaning that it is composed of several other types of materials. Concrete is composed of ceramics, such as lime and metals such as the stone in concrete called aggregate.
Concrete has a high compression strength, which is a material’s ability to withstand stress, which is usually around 3,000 to 6,000 psi. Concrete is strong because the ionic bonds that hold it together are the strongest types of bonds. Although concrete is durable concrete, it also has a low tensile strength, which is the amount of weight a material can withstand while being pulled or stretched before breaking, of around 300 to 700 psi. This is why many concrete structures must be reinforced by steel. Although the density of concrete varies with the ratio of aggregate to filler mixture, the density of concrete usually varies from 2,240 to 2,400 kg/m^3. Despite concrete’s high density and compression strength, concrete is brittle. The brittleness is caused by the dominant ionic bonds. In an ionic bond, the positive and negative charges line up against each other, forming a grid-like pattern. Therefore, if one atom slips out of place, all of the atoms are aligned incorrectly, causing the bonds to fall apart. Flexural strength is how much weight a material can suspend before breaking. Concrete has a flexural strength of 400 to 700 psi.
Concrete has a high compression strength, which is a material’s ability to withstand stress, which is usually around 3,000 to 6,000 psi. Concrete is strong because the ionic bonds that hold it together are the strongest types of bonds. Although concrete is durable concrete, it also has a low tensile strength, which is the amount of weight a material can withstand while being pulled or stretched before breaking, of around 300 to 700 psi. This is why many concrete structures must be reinforced by steel. Although the density of concrete varies with the ratio of aggregate to filler mixture, the density of concrete usually varies from 2,240 to 2,400 kg/m^3. Despite concrete’s high density and compression strength, concrete is brittle. The brittleness is caused by the dominant ionic bonds. In an ionic bond, the positive and negative charges line up against each other, forming a grid-like pattern. Therefore, if one atom slips out of place, all of the atoms are aligned incorrectly, causing the bonds to fall apart. Flexural strength is how much weight a material can suspend before breaking. Concrete has a flexural strength of 400 to 700 psi.