Smart laying mortars for masonry structures: effects of lime/cement ratio and carbon nanomaterials content on self-sensing behavior

The mechanical behavior of mortar joints directly affects the structural performance and failure mechanisms of masonry. Since previous research did not evaluate the effects of different lime/cement ratios on intrinsic self-sensing properties, this study developed a factorial experiment to investigate the electrical resistivity, gauge factor, stress sensitivity and compressive strength of mortars with different lime/cement proportions (0.25, 0,50, 1.00, 2.00, by volume) and carbon black nanoparticles (CBN) contents (0%, 3%, 6%, 9% by weight of binders). Results were explained based on X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (FEGSEM) analyses. Increases in lime content delayed the percolation threshold and decreased the mortars' strength. Portlandite and calcite structures of lime increased the distance between CBN, modifying the electron conduction mechanisms. At the end of the percolation zone, the addition of lime increased self-sensing properties, whereas the opposite behavior was observed at the beginning of the percolation zone.