Graphite-Cement Composites as Low-Cost Strain Sensing Multifunctional Materials

Graphite, an allotropic form of carbon with high electrical conductivity, in the range of \(2\times 10^5\) to \(3\times 10^5\) S\(\cdot \)m\(^{-1}\), is a more affordable alternative to carbon nanotube nanoinclusions in the fabrication of conductive multifunctional cement-based materials, such as smart concretes, used in strain monitoring. The enhancement of piezo-resistivity is one possible functionality of graphite inclusions that has not yet been explored in depth in the literature. In order to bridge this gap, the authors investigate the piezo-resistive strain-sensing response of graphite-cement composite materials. The composite samples were prepared with different amounts of graphite inclusions and experimentally subjected to electro-mechanical tests. The study discusses the improvements in conductivity, strain sensitivity, and signal linearity achieved with graphite inclusion. Because of the easier dispersion and lower cost of graphite particles, the investigated composites can be scaled up to large concrete elements, useful to create smart road pavements enabling intelligent weigh-in-motion sensing as intended in this research. Results demonstrate that multifunctional self-sensing composite pavements doped with graphite are capable of strain sensing with high linearity and sensitivity. In particular, it was found that a 20% graphite-to-cement ratio exhibited the best properties in terms of gauge factor, drift, reproducibility, and linearity.