Fabrication of Self-Sensing Carbon Fiber Cementitious Composites: Best Practices

Self-sensing cementitious composites are ideal for use as sensors in structural health monitoring of concrete structures because of their similar physical and mechanical properties to those of the host structure and their proven strain sensitivity. A conductive phase (such as carbon fibers, carbon nanotubes, carbon black, etc.) is typically incorporated into cement paste to obtain cementitious sensors. Previous research has mainly focused on proof-of-concept demonstrations of the strain-sensing properties of cementitious sensors. The sensitivity, repeatability, and stability of carbon fiber reinforced cementitious (CFRC) sensors are significantly influenced by the mix design and the quality of fiber dispersion. So far, fiber volume fractions and dispersion techniques have been specific to each research project. The main objective of this study is to provide a basis for developing a standardized mix design and fabrication procedure for CFRC sensors. First, the mix design and fabrication procedures used in previous research were reviewed and compared to identify the optimum fiber content and the most efficient balance of mechanical and chemical fiber dispersion techniques. The effect of a partial replacement of cement by supplementary cementitious materials was also examined in terms of the target rheological and workability properties. The second part of the study presents the results from a preliminary experimental investigation for evaluating the microstructure of CFRC sensors. Sensor samples were prepared by adopting the best fabrication practices identified in the first part of the study. The fiber dispersion quality was evaluated via several image processing techniques using combined reflection and transition optical and scanning electron microscopes.