Resistance heating using electrically conductive cements

Steel fibre (8 μm diameter, 0·72 vol.%)-reinforced cement was found to be effective for resistance heating. A DC electrical power input of 5·6 W (7·1 V, 0·79 A) resulted in a maximum temperature of 60°C (initial temperature = 19°C) and a time of 6 min to reach half the maximum temperature. Efficiency of energy conversion increased with time of heating, reaching 100% after 50 min. The heat power output per unit area was 750 W/m2 for steel fibre cement, compared with 340 W/m2 for a metal wire with the same resistance. The use of carbon fibres or graphite particles in place of steel fibres resulted in less effective heating, due to the higher resistivity.