Strain sensing ability of GNP reinforced cementitious composites: The role of exfoliation and interlayer spacing

[Display omitted] •Exfoliation of stacked GNPs to few-layers is essential for high strain sensing signal.•Ultrasonication energy effectively exfoliates multi-layer GNPs into tri-layers.•Interlayer spacing in stacked GNPs increases the permittivity of nanocomposites.•Number of GNP layers and permittivity relationship for loadings above percolation.•Efficient monitoring at elastic and post-elastic stage via piezopermittivity values. In this study, the effect of the exfoliation state of GNPs on the strain sensing capacity of GNP reinforced cementitious composites at the elastic and post-elastic stages of deformation is demonstrated. Below percolation threshold, effective exfoliation of multi-layer GNPs results in tri-layer nanomaterials. For GNP volume fractions above percolation a direct correlation between the number of exfoliated graphene layers and permittivity values of the cementitious nanocomposites exists. Electrochemical Impedance Spectroscopy (EIS) measurements demonstrated that the nanocomposite’s electrical energy storage capacity depends on the interlayer spacing between graphene nanosheets. Piezoresistivity experiments showed that the piezoresistive signal is independent on the strain levels at the post-elastic stage. Piezopermittivity results revealed an excellent relationship between the fractional change in permittivity and stress and strain values during the loading–unloading cycles at both the elastic and post-elastic stages. A direct relationship between piezopermittivity and volume fraction of tri-layer and multi-layer GNPs is also observed suggesting that the GNP content at the percolation threshold is optimum for maximizing the strain sensing capacity of the nanocomposite.