E-Lab July - September 1997

July - September 1997

Options for Using China's Coal in Cars: A Life-Cycle Assessment
[Abstract] [References]

Using Optical Fibers to Monitor the Health of Concrete Structures
[Abstract] [References]

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Options for Using China's Coal in Cars: A Life-Cycle Assessment

hinese policymakers face a bewildering array of options as they consider using their vast coal deposits to fuel vehicles. Coal can be used to produce gasoline, methanol, or electricity. But each of those fuels has its advantages and disadvantages. MIT researchers and their Chinese and American collaborators have now estimated how shifting from petroleum to each coal-based fuel would change consumer costs, environmental impacts, and energy efficiency. Their life-cycle analyses included the complete history of each type of fuel and vehicle, from extraction of raw materials through production, use, and disposal. As expected, changing to any of the coal-based fuels would reduce efficiency, increase carbon dioxide emissions, and cost more. However, the added cost is a relatively small fraction of the total cost of owning a vehicle--except in the case of electricity, which is prohibitively expensive unless batteries improve dramatically. Effects on emissions other than carbon dioxide vary from fuel to fuel. This type of comprehensive assessment represents a methodology that can also be used to compare technology options in other fields.

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Using Optical Fibers to Monitor the Health of Concrete Structures

ridges and other reinforced concrete structures inevitably crack before they fail. To look for cracks, owners of such structures perform periodic visual inspections--a technique that is both expensive and unreliable. Energy Laboratory and Brown University researchers are now developing a sensor that can automatically monitor concrete structures for cracking. The sensor involves an optical fiber placed on or within the concrete structure. When a crack forms, the fiber bends and light rays passing through it escape. By analyzing reductions in the light signal, the sensor indicates not only the existence of new cracks but also their sizes and locations. The sensor can detect multiple cracks all along the length of the fiber--a major advantage over other sensors being developed, which typically monitor only what happens at a particular point. Both laboratory experiments and computer simulations demonstrate the capabilities of the new sensor. Other experiments show that wrapping optical fibers around a rod produces a crack sensor that can be embedded into buried structures such as barriers for hazardous waste containment. In related work, the researchers are using chemical deposition techniques to produce optical fiber sensors that can detect strain (stretching or shortening) at a local point on a concrete structure under stress. The novel strain sensor is highly sensitive and a fraction the cost of optical strain sensors produced by conventional means.

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