In this paper, a self-sensing carbon nanotube (CNT)/cement composite is investigated for traffic monitoring. The cement composite is filled with multi-walled carbon nanotubes whose piezoresistive properties enable the detection of mechanical stresses induced by traffic flow. The sensing capability of the self-sensing CNT/cement composite is explored in laboratory tests and road tests. Experimental results show that the fabricated self-sensing CNT/cement composite presents sensitive and stable responses to repeated compressive loadings and impulsive loadings, and has remarkable responses to vehicular loadings. These findings indicate that the self-sensing CNT/cement composite has great potential for traffic monitoring use, such as in traffic flow detection, weigh-in-motion measurement and vehicle speed detection.

This paper studies the piezoresistive property of the CNT/cement composite to explore its feasibility as an embedded stress sensor for civil structures such as roadways, levees and bridges. The experimental results show that the electrical resistance of the CNT/cement composite changes with the compressive stress level, indicating the potential of using the CNT/cement composite as a stress sensor for civil structures. The piezoresistive responses of the composite with different fabrication methods and CNT doping levels were also studied. It is found that dispersion-assistant surfactants could block the contacts among carbon nanotubes, thus impairing the piezoresistive response of the composite, while a higher CNT doping level could improve the sensitivity of the composite stress response.

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Carbon nanotube (CNT)/cement composites with different concentration levels of multi-walled CNT (MWNT) and water/cement ratios are fabricated. By comparing the responses of electrical resistance of these CNT/cement composites to compressive stress, the effects of MWNT concentration level and water/cement ratio on the piezoresistive sensitivity of composites are investigated. Experimental results indicate that the piezoresistive sensitivities of CNT/cement composites with 0.05, 0.1, and 1 wt% of MWNT first increase and then decrease with the increase of CNT concentration levels. Water/cement ratio is another factor that affects the composite properties, the electrical resistance of CNT/cement composite with 0.6 water/cement ratio is more sensitive to compressive stress than that of composite with 0.45 water/cement ratio. The piezoresistive sensitivity is heavily dependent on the conductive network in the composites, which in turn is influenced by the CNT concentration level and water/cement ratio.

In this paper, a self-sensing carbon nanotube (CNT) concrete pavement system for traffic detection is proposed and tested in a roadway. Pre-cast and cast-in-place self-sensing CNT concrete sensors were simultaneously integrated into a controlled pavement test section at the Minnesota Road Research Facility (MnROAD), USA. Road tests of the system were conducted by using an MnROAD five-axle semi-trailer tractor truck and a van, respectively, both in the winter and summer. Test results show that the proposed self-sensing pavement system can accurately detect the passing of different vehicles under different vehicular speeds and test environments. These findings indicate that the developed self-sensing CNT concrete pavement system can achieve real-time vehicle flow detection with a high detection rate and a low false-alarm rate.