Electrically Conductive Concrete: Properties and Potential

Published in Construction Canada, v. 98, no. 1, Jan./Feb., 1998, pp. 28-29

Abstract: Conductive concrete is a cement-based composite that contains electronically conductive components to attain stable and relatively high conductivity. Potential applications include electrical heating for de-icing of parking garages, sidewalks, driveways, highway bridges, and airport runways, as well as electrical grounding.

Résumé: Le béton conducteur est un composite à base de ciment contenant une certaine quantité d’éléments qui assurent une conductivité électrique stable et relativement élevée. Les applications possibles sont : le chauffage électrique pour dégivrer les garages de stationnement, les trottoirs, les voies d’accès, les ponts routiers et les pistes d’aéroport, et la mise à la terre électrique.

Overview

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.

Ongoing IRC research is now focused on optimizing conductive concrete formulations for the best combination of strength, electrical properties, and production methods at the lowest possible cost, leading ultimately to commercial development and widespread use.

Properties

Conductive concrete is a cement-based composite that contains a certain amount of electronically conductive components to attain stable and relatively high conductivity. In essence, the aggregates normally used in concrete can be largely replaced by a variety of carbon-based materials to achieve electrical conductivity in conductive concrete. This is achieved while retaining the desired engineering properties, as indicated in Table 1. The conductivity is usually several orders of magnitude higher than that of normal concrete. Normal concrete is effectively an insulator in the dry state, and has unstable and significantly greater resistivity characteristics than conductive concrete, even when wet.

Table 1. Conductive Concrete Properties

Electrical Resistivity (omega – cm)	1 – 40
Compressive Strength (MPa)	30 minimum
Flexural Strength (MPa)	5 – 15
Density (kg/m3)	1450 – 1850

Conductive concrete can be produced using conventional mixing techniques. The mixing process can be controlled, permitting design of mix formulations that are reliably repeatable, and achieve electrical resistivity values within the overall target design range.

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. Several of these promising applications are described more fully below.

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.

As part of the pre-commercial development process, an outdoor heated area 13 m X 3 m, roughly the size of a small driveway, was built with an embedded conductive concrete layer (Figure 1). The surface area has been kept continuously dry and free of snow over the course of most of an Ottawa winter, successfully melting over 3.5 m of total snow accumulation, and providing a scale proof of concept for conductive concrete de-icing applications.

The possibility also exists for using conductive concrete as an indoor radiant heat option. Both de-icing and radiant heating uses will require appropriate changes to the Canadian electrical code before commercial use in public areas becomes established.

Electrical grounding. Grounding is required for virtually every electrical installation. The main purpose of electrical grounding is to protect the equipment and occupants in the event of an electrical systems failure, or in special situations such as the presence of lightning or static electricity. The protection is achieved through a proper electrical connection between the systems usually by embedding an electrode underground.

The establishment of an effective, economical and durable electrical grounding system has always presented problems for the electrical engineer, but now many of them can be solved through use of conductive concrete. Conductive concrete grounding uses include creation of equipotential floors in such disparate applications as dairy barns, where small voltage differences can reduce production, through to electronics fabrication and handling areas, where the potential for costly damage to high-value semi-conductors and associated equipment caused by static charges can be high.

With its excellent structural engineering properties, conductive concrete is also a good candidate for grounding in a variety of utility uses. These include communications, and electrical transmission towers, as well as electrical transformer locations.

Commercial Development

IRC’s continuing research on conductive concrete and interest in licensing the use of this innovative new technology offers opportunities for progressive organizations to gain a competitive advantage in developing new products and improving existing ones in a variety of markets. IRC welcomes expressions of interest in the development of conductive concrete. For further information concerning conductive concrete, please contact Mr. Mark Arnott at 613-993-9811 (tel) /613-954-5984 (fax) /or e-mail at mark.arnott@nrc.ca

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This paper is a contribution from the National Research Council of Canada, Institute for Research in Construction.
Cet article a été fourni par l’Institut de recherche en construction du Conseil national de recherches Canada