Influences of multi-walled carbon nanotube (MCNT) fraction, moisture, stress/strain level on the electrical properties of MCNT cement-based composites

Multi-walled carbon nanotube (MCNT) cement-based composites (MNTCCs) with seven different volume additions of MCNT (V) were prepared with surfactant ultrasonic dispersion process. A Wheatstone-based data acquisition technique was developed to simultaneously obtain the electrical resistances, the uniaxial stresses (σ_c), and the longitudinal strains (ε_l) of the cured MNTCCs under compressive loading. The percolation threshold, humidity impact on initial resistivity (ρ_in), and self-sensing piezoresistivity under mono- and cyclic-loading of the MNTCCs were correspondingly investigated. Results reveal that, the ρ_in of MNTCC successively conforms to tunneling transition and percolation effect along with V increment; Fraction change in resistivity (Δρ) of MNTCCs with 1.31 vol.% MCNT (round percolation threshold) after excluding humidity impact can steadily and linearly alter with σ_c or ε_l, and effectively reflect the microstructure changes and crack emerging; The corresponding strain sensitivity, reproducibility of the Δρ-ε_l curve can maintain above 132, less than 5%. These consequences favor the MNTCCs to be intrinsic sensors applied in infrastructure for real-time monitoring of cyclic loadings with high sensitivity, stable and fast responses.