Influence of water-cement ratio on electrical properties of smart cement composites

This study presents the results of research on the influence of the water-to-cement ratio [w/c] on the electrical properties of cement composites with expanded graphite [EG]. The analysis was conducted on samples containing 2 % to 6 % EG, with w/c ratios ranging from 0.40 to 0.60. The experimental program included four-point probe resistivity measurements, impedance spectroscopy, as well as evaluation of the thermoelectric and self-heating properties of the composites. The results indicate that increasing the w/c ratio leads to a reduction in the electrical conductivity of the studied composites, regardless of the EG content. Impedance spectra analysis showed that, within the investigated w/c range, the percolation threshold is exceeded in composites containing more than 4 % EG. The higher the EG content, percolation threshold is exceeded at higher w/c. An important observation is weakly formed semicircles in Nyquist plot for composites in the percolation zone. The closer conductivity of the composite is to the percolation threshold, the less distinct the semicircle. This characteristic spectrum shape allows for the determination of the conductive additive content in the percolation zone. Furthermore, the findings confirm that the w/c ratio significantly influences the self-heating properties of the investigated cement composites. In contrast, the w/c ratio does not appear to affect the magnitude of the Seebeck coefficient above the percolation threshold. The obtained results clearly indicate the significant role of water-to-cement ratio in shaping the functional properties of these materials.