La piezoresistività dei compositi cementizi rinforzati con nanotubi in carbonio

Carbon nanotubes (CNT) are based on one or more sheets of graphite rolled up into a tube. Adding carbon nanotubes, the electrical resistivity of cementitious composites changes by varying the stress conditions. Variation in the electric resistivity can be ascribed to the increase in the number of contact points of CNTs by increasing loading: the higher the compressive stress, the higher the contact points, the lower the resistivity. This particular CNT behaviour can be used to evaluate the level of stress in reinforced concrete structures, to monitor the traffic flow, to weigh vehicles, to control the entrance in restricted areas, to switch on electrical or heating equipments. In the present work data on rheological and mechanical properties, electrical resistivity and pressure-sensitive behaviour under cyclic compressive loading of cement composites containing multi-walled carbon nanotubes (MWNT) are presented. Results show that carbon nanotubes improve the flexural and compressive strength of cementitious composites only if they are efficiently dispersed. In fact, in order to form a conductive network and enhance the piezoresistive properties of cementitious mixtures, Carbon NanoTubes (CNTs) were dispersed in the cement matrix by two different methods: only by sonication and by a surfactant (LAS) in an aqueous solution. At the end of the mixing procedure, a defoamer (tributyl phosphate) was added in order to decrease the air bubble in MWNT filled cement-based composites created by the surfactant. Moreover, the addition of CNTs leads to a notable decrease in volume electrical resistivity and enhances the pressure sensitivity of the cementitious mixtures. Experimental results show that the electrochemical impedance changes synchronously with the compressive stress levels for all the specimens. Moreover, the piezoresistive response is better for cement composites and increases adding more CNTs percentage.