Self-sensing Cementitious Composites for Monitoring Concrete Beams under Bending

An electrically conductive filler can be mixed into a cement-based matrix to create a self-sensing cementitious composites (SSCC). Carbon-based materials, such as graphene, carbon fiber, and carbon nanotubes (CNT), are the most commonly used fillers for this purpose. Concrete structures can be monitored through the changes in the SSCC electrical resistivity by taking advantage of its piezo-resistive behaviour. It has been proposed that the correlation between deformation and resistivity can be used as a calibration equation for the SSCC, which in turn, can be embedded in structural elements for monitoring. The purpose of this study was to develop a calibrated SSCC with CNT as conductive filler and apply it in the monitoring of a concrete beam subjected to cyclic bending. Cement, sand, CNT, and a viscosity modifying agent were combined to produce a SSCC that was molded in 4 cm side cubes with four copper electrodes inserted to measure its electrical resistivity. A Self-compacting concrete beam (10 × 10 × 40 cm) was molded with the cubic SSCC embedded in the compressed zone, cured for 28 days, and then submitted to cyclical four-point bending tests by increasing progressively the applied load until reaching the maximum flexural strength of the material. Strain gauges were installed on both the SSCC and the concrete beam. The effectiveness of the developed SSCC to monitor the concrete beam was demonstrated through the proportional response between the electrical resistivity of the SSCC and the mechanical load applied to the concrete beam. It was concluded that regardless of non-uniform deformations under bending, the compressed zone of concrete beams subject to bending may be effectively monitored by the SSCC.