Purdue News
Purdue News
|
|
March 27, 1992 High-tech cement may save roads, reduce cost of microchipsWEST LAFAYETTE, IND. -- Potholes and crumbling bridges soon may be problems of the past, while higher high-rise buildings and microchips made from cement-based materials could be the wave of the future. These are a few of the innovations under way at a consortium of Midwestern institutions that recently received a $1O million National Science Foundation renewal grant to develop high-tech cement-based materials. At Purdue University, a member of the consortium, scientists are concentrating on the microscopic structure of concrete and factors that affect its durability. One of the keys is water. "The less water used to mix the concrete, the stronger it will be," says Sidney Diamond, professor of engineering materials at Purdue. "But the details of what happens when water is added isn't really understood as well as it should be. Hopefully we can learn more that will enable us to control the process." At Purdue, researcher uses chemical methods to minimize the amount of water needed to mix with dry concrete. The aim is to maximize strength while still retaining enough moisture to make the resulting mixture flow well enough to become properly coherent and firm. To reduce the water content, Diamond studies the effects of materials called superplasticizers in combination with silica fume in the cement-based materials. Use of such substances, called admixtures, in concrete significantly increases the strength of the material. This line of research at Purdue and elsewhere already has paid off in that some suppliers of building materials now can deliver ready-mix high-strength cement that can support stresses of up to 20,000 pounds per square inch, a four-fold improvement over ordinary concrete. In addition to examining methods of increasing strength, Purdue researchers also are investigating the durability aspects of highstrength concrete, since less water added to the material also makes it more durable. As part of this research, Menashi D. Cohen, associate professor of civil engineering, and William L. Dolch, professor of engineering materials at Purdue, are investigating the freezing resistance and durability of high-strength concrete. They are working to reduce the pressure that develops when water in concrete alternately freezes and thaws. This freezing and thawing causes the concrete to crack and deteriorate, producing potholes in roads, crumbling bridges, cracked driveways and leaky water mains. "One approach to these problems," Cohen says, "is to reduce the amount of water to such a low point that the water could not freeze inside the concrete and pressure could not build up." This would reduce the chance of cracking and of additional water seeping into the cracks to cause more damage. The new high-tech cement not only has applications for roads and bridges, but also in high-rise buildings. "When you use high-strength concrete in buildings, you can reduce the size of your columns," says Cohen. "This makes the building not only taller and leaner, but also increases rentable floor space." These very strong and wear-resistant materials are used in other things as well, such as in aircraft engine covers. High-strength concrete also is used to improve abrasion resistance in pipelines through which powdered solids are blown, and to provide blast resistance in concrete missile silos. In addition to being super-strong and even flexible, some of the new advanced materials have electrical insulating properties similar to those of the silicon used in today's computer microchips. "Considerable work has been done on using cement-based materials as computer chip substrates," says Diamond. The computer chip substrate is the material on which a tiny electrical circuit is etched. "Chips made from silicon tend to be brittle and break during the manufacturing process," Diamond says. "Since the cement-based material is stronger, the manufacturing losses might go way down, making cementbased microchips more economical to produce." Diamond heads a research team representing Purdue in the Center for Science and Technology of Advanced Cement-Based Materials. In addition to Purdue, the consortium of institutions in the center are the University of Illinois, the University of Michigan, the National Institute of Standards and Technology, and Northwestern University, where the center is based. Note: Photographs of the researcher and a microscopic image of cementbased material are available. Purdue News Service: (765) 494-2096; purduenews@purdue.edu
|
