31-10-2012, 02:43 PM
ELECTRICALLY CONDUCTIVE CONCRETE: ITSPROPERTIES AND POTENTIAL
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WHAT IS ELECTRICALLY CONDUCTIVE CONCRETE?
Although concrete has existed in various forms over most of recorded history, it is a material that still has opportunities for exciting developments. Over a number of years, many unsuccessful research efforts were made to develop concrete that could combine good electrical conductivity with the excellent engineering properties of normal concrete mixes. The Institute for Research in Construction (IRC) has succeeded in achieving this challenging goal, with electrically conductive concrete (”conductive concrete” for short), a patented invention that offers future promise for use in a variety of construction applications.
CHARACTERISTICS:
While the engineering properties and mixing characteristics of conductive concrete and normal concrete are comparable, conductive concrete does have other distinctive characteristics beyond its ability to conduct electricity.
The conductivity value is stable. The effects of moisture content, hydration time and temperature on conductivity are insignificant.
It is lightweight: conventionally mixed, conductive concrete has a density of about 70 percent that of normal concrete.
Conductive concrete is chemically compatible with normal concrete, bonding well with it if used as an overlay.
Thermal stability is comparable to that of normal concrete.
The colour of conductive concrete is a darker grey, reflecting its carbon content.
APPLICATIONS:
Conductive concrete has the potential to address a wide variety of applications, including grounding, heating, cathodic protection of reinforcing steel in concrete structures such as bridges and parking garages, and electromagnetic shielding.
Electrical heating: Electrical heating using conductive concrete has excellent potential for domestic and outdoor environments, especially for de-icing of parking garages, sidewalks, driveways, highway bridges, and airport runways. This method of heating would eliminate or dramatically reduce the need for using salt, thus providing an effective and environmentally friendly alternative. Conductive concrete itself is the heating element, and thus is able to generate the heat more uniformly throughout the heated structure.
INCREASING CONDUCTIVITY WITHOUT STRENGTH PENALTY:
An entirely different concept is to use a conductive aggregate in place of conventional aggregates. Such an aggregate must have low resistivity, adequate mechanical strength, proper particle grading, low sulphate and chloride contents, chemical inertness at normal temperature and pressure, a pH value not less than 7 and low water absorption.
Graphite is a possible material, but it meets only some of the requirements. Three reasons against its use are that it is high in cost, it is presently unavailable as an aggregate in the necessary gradings, and the concrete made with it have insufficiently low electrical resistance.