Electrically conductive cement-based materials

Abstract

Electrically conductive cement-based materials are useful for electrical grounding, lightning protection, resistance heating, static charge dissipation, electromagnetic interference (EMI) shielding, cathodic protection, and thermoelectric energy generation. The science and applications of electrically conductive cement-based materials are reviewed. In addition, a comparative study of the effectiveness of various electrically conductive admixtures (discontinuous forms of steel and carbon) for lowering the electrical resistivity of cement shows that the effectiveness decreases in the order: steel fibre of diameter 8 μm, steel fibre of diameter 60 μm, carbon fibre of diameter 15 μm, carbon nanofibre of diameter 0·1 μm, coke powder (< 75 μm) and graphite powder (< 1 μm). For EMI shielding, the effectiveness decreases in the order: steel fibre of diameter 8 μm, coke powder (< 75 μm), carbon nanofibre of diameter 0·1 μm, graphite powder (< 1 μm), steel fibre of diameter 60 μm, carbon fibre of diameter 15 μm, and steel dust of size 0·55 mm. By using steel fibre (8 μm diameter) at 0·72 vol.%, a resistivity of 16 Ω cm and an EMI shielding effectiveness of 59 dB (1 GHz) were attained. The carbon admixtures cause the absolute thermoelectric power to be more positive, whereas the steel admixtures can cause the absolute thermoelectric power to be more positive or more negative. In particular, steel fibre of diameter 60 μm at 0·2 vol.% causes the absolute thermoelectric power to be strongly negative (−63 μV/°C). Moisture loss has no effect on the absolute thermoelectric power, but increases the resistivity.