Effect of monodoped/multi-doped carbon nanotubes and nano-titanium dioxide on mechanical and self-sensing properties of sulfoaluminate cementitious composites

The multi-walled carbon nanotubes (MWCNTs) and anatase nano-titanium dioxide (NT) are excellent fillers for the preparation of self-sensing cement-based materials. Moreover, compared with ordinary Portland cement, sulfoaluminate cement has the advantages of low carbon, corrosion resistance and rapid strength development, and the cement-based material can obtain more stable self-sensing performance when used as a matrix. Therefore, this paper prepared sulfoaluminate cement mortar specimens using NT and MWCNTs in either single-addition or double-addition form. Then, the effects of different conductive fillers on the mechanical properties, electrical properties and self-sensing properties of the sulfoaluminate cementitious composites were studied at 3d, and the mechanisms were analyzed by SEM-EDS. The results show that the early mechanical properties of sulphoaluminate cementitious composites were significantly improved by adding NT. Compared to the control group, the compressive strength, flexural strength, splitting tensile strength, and compressive toughness of the cementitious composites with NT increased by 28.36%, 10.67%, 47.76%, and 9.53% , respectively. The single-addition of MWCNTs has the most significant effect on improving the conductivity. Compared with the control group, the DC resistivity and AC resistivity at a frequency of 100 kHz decreased by 46.91% and 63.87%, respectively. The double-addition of MWCNTs-NT has the most significant effect on improving the self-sensing properties of the sulfoaluminate cementitious composites. Compared with the control group, the maximum fractional change in resistivity, stress and strain sensitivity of the sulfoaluminate cementitious composites with MWCNTs-NT under monotonic compression load and splitting tensile load increased by 235%, 211%, 313%, and 44%, 65%, 648%, respectively. SEM-EDS showed that in terms of compactness, the mortar with NT> control group> mortar with MWCNTs-NT > mortar with MWCNTs, and in terms of the sensitivity of conductive network changes, the mortar with MWCNTs-NT > mortar with NT > mortar with MWCNTs.