Piezoresistive performance of 3D printed cementitious composites doped with carbon microfibers

The development of additive manufacturing technology in concrete construction is mainly driven by its intrinsic characteristics compared with conventional concrete. Such characteristics hold benefits related to reduced waste and workforce, and higher productivity. Despite being a promising technology, there are still challenges preventing its exponential growth in full-scale construction applications, such as the scalability of the technique and specific characteristics of the materials produced. One of the main concerns regarding the development of printed cementitious composites is related to the anisotropy of the material since their production involves the deposition of different layers of cementitious material, each one formed by filaments, which can result in weak bonds in the areas of contact. There is an opportunity in leveraging Structural Health Monitoring (SHM) technologies. SHM has been widely studied in the past years, with special attention to the development of multifunctional materials that can behave as sensors, such as cementitious and lime-based materials with piezoresistive capabilities, that can be sensitive to stress and strain variations through changes in resistivity. In these terms, the development of multifunctional cementitious materials through 3D printing (3DP) can represent an advance in the field since the higher mechanical robustness can contribute to the scalability of the sensor production, and in general terms, its widespread adoption. The current work seeks to compare the piezoresistive performance of printed specimens of cement mortar and paste produced under the same printing parameters, with and without carbon microfibers (CMF), as well as their piezoresistive behavior in comparison with cast cement-based samples, produced with the same content of carbon microfibers. As a result, the 3DP mortar samples containing CMF exhibited a significant increase in sensitivity compared to those without this carbon filler, a trend not observed in the 3DP pastes containing CMF when compared to those without. While the 3DP samples were slightly less sensitive than their manually produced counterparts, they still demonstrated strong performance as sensors.