Effect of internal moisture on self-heating properties of smart cement composites

The paper investigates the effect of moisture on the self-heating properties of smart cement composites with the addition of expanded graphite (EG), which is very important in terms of practical use of these composites. For this purpose, a series of cement pastes with different graphite content were made. Self-heating tests were conducted on prepared cement pastes with different water content. In these tests, the surface temperature was measured during 1000 s. The maximum temperature of the composites, the power per area, and the heating rate were determined. Cyclic heating of the composite to 40 °C was also carried out. Additionally, impedance spectroscopy (IS) was applied to analyze electrical properties to determine the reason for the deterioration of the self-heating properties. The study showed that the self-heating properties of composites with expanded graphite deteriorate with increasing moisture. The maximum temperature, heating rate and power of the composites decrease with increasing water content in matrix. The self-heating properties deteriorate for composites with EG content both in the percolation range and above the percolation threshold. The IS analysis of the results suggests that the deterioration of the self-heating properties is probably due to polarization phenomena occurring when a DC voltage supply. The obtained results are crucial for the practical application of cement composites as resistive heating elements, particularly for outdoor applications.