SECURITY experts looking to prevent spies from eavesdropping on computers by intercepting the electromagnetic waves they throw off don't turn to Martha Stewart for interior-design inspiration. The solutions they employ are often unattractive and well beyond even her budget. For example, one involves building a room within a room out of welded thick steel plates.
But a new concrete that can conduct electricity may make it possible to construct buildings in which the basic structure does double duty as an electromagnetic shield.
Not that the scientists who developed conductive concrete at the National Research Council of Canada were looking to play a role in the world of counterespionage.
''The initial development evolved from a discussion I had with a graduate student,'' said James J. Beaudoin, the lead researcher and a concrete expert at the research council's Institute for Research in Construction, based in Ottawa. ''We were trying to come up with projects to address the needs of people in cold climates, such as snow and ice melting.'' Concrete that could conduct electricity would also create heat through resistive heating.
Of course, electrical elements and pipes carrying heated liquids have long been embedded in concrete to create ice-free garage ramps and walkways. But such installations are expensive and difficult to repair.
Nor, Dr. Beaudoin acknowledges, is the idea of a concrete that can carry electricity a particularly novel one. ''But most of the concepts developed in the past wouldn't be useful because you couldn't build anything with them,'' he said. ''They didn't have structural integrity.''
Early on, Dr. Beaudoin and other researchers at the research council looked into using carbon fibers similar to those that are woven into special fabrics and covered with resins to create lightweight but strong parts for aircraft and sports equipment.
Less exotic fibers have long been used in concrete for a variety of purposes, like increasing its ability to deform without shattering. The lab did eventually come up with a concrete mix that retained its strength after the addition of the carbon fibers and gained the ability to conduct electricity evenly -- a property that Dr. Beaudoin calls percolation.
But as anyone who has seen the price tag of a carbon-fiber-composite bicycle knows, carbon fibers are expensive. ''You have to remember we are dealing with a construction material here,'' Dr. Beaudoin said.
The group found a much cheaper substitute in coke breeze. Coke is essentially coal that has been reduced mostly to carbon by high-temperature baking. Most of the time it is added to blast furnaces at steel mills. Coke breeze is the leftover material that is too small for the steel industry. With coke breeze, the lab was able to create a conductive concrete that is only two to three times more expensive than ready-mix concrete.
Finding a suitable additive proved to be only half the problem. Mark Arnott, the conductive concrete project manager, said that a far bigger issue was developing special mixing, handling and curing processes that ensure consistent electrical conductivity between different batches of the concrete. ''We could give you the recipe but you would most likely not be able to produce the material,'' he said. (The recipe would not make light reading in any case. The manual on making and using the conductive concrete runs about 400 pages.)
Because of the complexity of creating this concrete, St. Lawrence Cement, a Swiss-owned company based in Montreal that has licensed the technology, initially plans to offer it only in precast pieces.
Except for the positive and negative leads embedded in them, St. Lawrence's conductive concrete slabs look much like those sold at The Home Depot. At the offices of a construction company in Oakville, Ontario, owned by St. Lawrence, the concrete company built a sidewalk and a loading ramp to test the material late last year.
The winter has been unusually mild, so the system has not been overwhelmed by snow. But Peter J. Tumidajski, the manager of new product development for St. Lawrence, said that the eight times it did snow, the self-heating ramp was never more than slushy. ''You never actually get a buildup of snow,'' he said. ''It always keeps up.'' A 20-by-80-foot pad at the National Research Council's far more wintry grounds in Ottawa melted the snow and ice without fail for three years.
Although a relatively high voltage is used, the actual current flowing through it is small because of the high resistance of the concrete. So it is safe to touch the concrete.
St. Lawrence is dreaming of bigger things than loading ramps, however. Dr. Tumidajski hopes that the material, encased in two layers of conventional concrete, will be laid on the decks of highway bridges. The system would have two functions. When relatively high-voltage electricity was sent through it, it would melt ice and snow. But a much lower voltage could be sent through the concrete to inhibit the electrochemical corrosion of the steel reinforcing bars that are buried in it.
Several Canadian and United States government agencies, including the United States Army Corps of Engineers, have approached the research council about using conductive concrete to trap computer signals. While a variety of technologies are used within computers and monitors to limit the amount of electromagnetic radiation they throw off, high-security facilities are generally housed within something called a Faraday cage. In effect, this involves surrounding the room with metal, ranging from aluminum or copper mesh for less-secure facilities to one-quarter-inch-thick steel plate in more high-security applications.
Whatever their proportions, all Faraday cages work on the principle that a room made of a grounded, electrical conducting material will block electromagnetic waves from escaping.
Dr. Beaudoin and Mr. Arnott said there was no doubt that the conductive concrete could block emissions. ''But we don't have any hard data on how such a system will react,'' Mr. Arnott added. Research is now under way to come up with precise measurements of the concrete's efficiency.
There is one immediate use for conductive concrete. But it makes the prototype loading ramp -- not to mention the counterespionage applications -- seem positively glamorous. In rocky areas, it is often difficult to ground radio towers so that energy will dissipate when lightning strikes. One solution, Mr. Arnott said, is ''to just pour a trough of conductive concrete at the base.''
Photo (Mary Ann Smith)