The influence of carbon nanotubes dispersion on stress sensitivity of cementitious composites materials

Adding carbon nanotubes to the cement matrix, the electrical resistivity of cementitious composites changes with the stress conditions under static and dynamic loads. This particular behaviour can be used to evaluate the stress level in reinforced concrete structures, to monitor the traffic flow, to weigh vehicles. In this paper data on pressure-sensitive behaviour under compressive stress of cement pastes and mortars containing different percentages (from 0.1% to 1.0% vs cement mass) of MWNTs are presented. In order to form a conductive network and enhance the piezoresistive properties of cementitious mixtures, Carbon NanoTubes (CNTs) need to be efficiently dispersed in the cement matrix. Two different methods to disperse CNTs in the cement matrix were used: the first one schedules a 10 minutes sonication by an ultrasonic generator of a solution containing CNTs and about 50% of the mixing water and the second one uses a surfactant. The piezoresistivity properties of the cementitious mixtures manufactured with the two CNTs dispersing methods will be compared. Experimental results show that the piezoresistive response is better for cementitious composites manufactured by using the surfactant agent to disperse CNTs. Data indicate that – thanks to the better dispersion of nanotubes promoted by the surfactant - the pressure-sensitivity properties of cement pastes can be achieved even by using a very low percentage of CNTS (0.1% vs cement mass). These findings seem to indicate that self-sensing CNTs/cement composite can be produced. These smart materials have great potential and they could be used in the next future in concrete field for practical applications.