Strain monitoring for a bending concrete beam by using piezoresistive cement-based sensors

Graphite nanoplatelets (GNPs), promising in improving electrical properties of cement-based materials and its smartness, were used to prepare piezoresistive cement-based strain sensors (PCSSs) in this study. Their piezoresistive responses along vertical, horizontal and inclined directions were measured during applying a vertical cyclic compression. After calibrating free PCSSs by analyzing their gauge factors, three PCSSs are embedded in a four-point bending beam at different stress zones, i.e. uniaxial compression, uniaxial tension and combined shear and compression. In addition to investigating piezoresistive responses of PCSSs embedded in the beam, traditional strain gauges and finite element method (FEM) were also used to grasp the strains at relevant positions for comparison. For free PCSSs, It was found that the electrical resistances along vertical, horizontal and diagonal directions drop by amplitudes of 5.5%, 1.8% and 6.7% respectively, as the increasing of vertical compression. The gauge factor along loading direction was calculated to be −160.8, which illustrated a better sensitivity. In the four-point bending beam, the PCSSs in compressive zone and tensile zone can be used to presume the strain variation by considering the gauge factor obtained from the free PCSS. The reaction of the PCSS in shear zone can illustrate its strain features because a slight volume variation happened in this area, which can also be testified to be only 0.012"°with FEM analysis.