Flexible Enough to Withstand Earthquakes
Written by Dave Harcourt
http://ecoworldly.com/2009/04/23/self-healing-flexible-cement-invented/ April 23rd, 2009
Concrete that maintains itself by healing cracks improves the sustainability of infrastructure through its longer service life and lower maintenance inputs. Now researchers have developed flexible, self healing cement that won't suffer catastrophic failure when strained in an earthquake. We are so used to seeing maintenance teams working on our concrete buildings and structures that this expensive and carbon and energy intensive operation is taken for granted. But what if these structures could maintain themselves just as our bodies do when they heal cuts and scrapes? Dr Victor C. Li of the University of Michigan felt that this could be achieved through the development of new concretes. Self-healing cement is not a new idea. There is evidence of healing even in some ancient Roman buildings. However, it very seldom occurs with modern concrete and concrete designs. Very small cracks, preferably less than a tenth of a millimetre (four thousanths of an inch) wide are able to heal themselves. This happens when cement particles that were previously unexposed to air and water become exposed on the surfaces of the crack. These particles react with water in the air and CO2 to form sufficient calcium carbonate to fill the crack and bond on both sides. These healed cracks appear as white scars on the concrete surface. The healed concrete has properties which are equal to or better than those of the concrete before it was stressed and cracked. Dr Li and his team developed a bendable, engineered cement composite (ECC) that is much more flexible than traditional concrete. Traditional concrete can suffer catastrophic failure when strained in an earthquake or by routine overuse, but flexible ECC bends without breaking. Its properties are a result of specially coated reinforcing fibers that hold it together. The beauty of ECC structures would be that most maintenance would need no intervention and would occur continually, so long as the concrete is moistened periodically. Also the concrete doesn't require any reinforcing steel so the corrosion problem that has plagued the USA's reinforced concrete infrastructure is essentially eliminated. ECC can also be used to make buildings, bridges and roads more resistant to earthquakes, explosions and other extreme stresses thereby protecting lives. It will increase the service life of infrastructure and vastly reduce maintenance. This will have a significant effect on infrastructure's lifecycle carbon and energy footprints improving the sustainability of the world's infrastructure.
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