A Three-Dimensional Strain Rosette Sensor Based on Graphene Composite with Piezoresistive Effect

Obtaining the internal stress and strain state of concrete to evaluate the safety and reliability of structures is the important purpose of concrete structural health monitoring. In this paper, a three-dimensional (3D) strain rosette sensor was designed and fabricated using graphene-based piezoresistive composite to measure the strains in concrete structures. The piezoresistive composite was prepared using reduced graphene oxide (RGO) as conductive filler, cellulose nanofiber (CNF) as dispersant and structural skeleton, and waterborne epoxy (WEP) as polymer matrix. The mechanical, electrical, and electromechanical properties of RGO-CNF/WEP composite were tested. The results show that the tensile strength, elastic modulus, and conductivity of the composite are greatly improved by the addition of RGO and CNF. The relative resistance change of composite films demonstrates high sensitivity to mechanical strain with gauge factors of 16-52. Within 4% strain, the piezoresistive properties of composites are stable with good linearity and repeatability. The sensing performance of the 3D strain rosette was tested. The measured strains are close to the actual strains of measure point in concrete, and the error is small. The RGO-CNF/WEP composite has excellent mechanical and piezoresistive properties, which enable the 3D strain rosette to be used as embedded sensor to measure the internal strain of concrete structures accurately.