Concrete has been used for many years as a composite material that has excellent mechanical properties and durability for construction. However, concrete is a poor electrical conductor, especially under dry conditions. Concrete that is excellent in both mechanical and electrical conductivity properties may have important applications in the electrical, electronic, military and construction industry (e.g. for de-icing road from snow). Traditional methods can warm roads, but installation cost is high and the procedure is complicated.

The Technology

A research team in Material Laboratory of Institute for Research in Construction, National Research Council Canada, led by Dr. James J. Beaudoin, has developed a new conductive concrete with both superior electrical conductivity and mechanical properties.

The principle behind it is the use of cement to bind together electrically conductive materials such as carbon fiber, graphite and 'coke breeze' - a cheap by-product of steel production - to make a continuous network of conducting pathway. The design formulation is based on the 'electrical percolation' principle by which the composite conductivity increases dramatically by several orders of magnitude when the content of the conductive phase reaches a critical 'threshold' value. Further increases in the conductive phase content boost composite conductivity only slightly. The design specifies an amount just over the threshold content, assuring high conductivity and mechanical strength as well as good mixing conditions.

Conductive concrete particles and fibers are added to conventional aggregate and cement paste compositions to achieve the conductive concrete, which can be fabricated by two methods. The first one is by conventional mixing, which has relatively higher resistivity and high compressive strength. The second one is by slurry infiltration. This method can increase compressive and flexural strengths, and lower resistivity can be obtained.

The conductive concrete can be used as a structural material and bonds well with normal concrete. The conventional mixing type is lightweight, with only 70 per cent of normal concrete weight. Thermal stability is comparable to normal concrete, production employs conventional mixing and casting equipment, and application of the conductive concrete is similar to that of conventional concrete.

The conductive concrete could be used along with specially configured electrodes and an electric power supply to provide de-icing on roads, sidewalks, bridges and runways. Placed as an overlay, conductive concrete with very low resistivity can be used as a secondary anode in existing cathodic protection systems, providing uniform current distribution over its large surface area and reduced anodic current density.