Self-sensing Carbon Nanotube Cement-based Composites And Their Application In Traffic Detection

Carbon nanotube(CNT) has excellent physical properties including mechanical,electrical and thermal behaviors and good chemical stability. Moreover, it possessesunique hollow tube structure, nanoscale diameter and high aspect ratio. These makeCNT become excellent nanoscale filler for fabricating self-sensing cement-basedcomposites. Owing to such advantages as convenient fixing, excellent compatibilitywith concrete pavement, excellent durability, easy maintenance, etc, CNT cement-basedcomposites have widely potential application in the field of traffic detection. This studymainly focuses on the preparation of CNT cement-based composites withsuperplasticizer, the test of sensing property of CNT cement-based composites, thenumerical simulation of electrical property of CNT cement-based composites, and thetraffic flow detection based on CNT cement-based composites. Main contents of thisthesis are as follows:(1) Aiming at the compatibility between CNT/carbon nanofiber (CNF) dispersantand cement matrix, superplasticizer is used to improve the dispersion of CNT/CNF andfabricate the self-sensing CNT/CNF cement-based composites. Test results of sensingproperty of composites with different concentrations and types of CNT/CNF indicatethat the use of superplasticizer to fabricate self-sensing CNT/CNF cement-basedcomposites is feasible due to its double dispersion mechanism.(2) Aiming at the acquisition of the sensing signals of CNT cement-basedcomposites, the conductive characteristic (including electrical resistance andcapacitance) of the composites is studied. The response of resistance and capacitance tocompressive loading is tested, and the effect of AC voltage on sensing property is alsoinvestigated. Based on the above research results, an extraction method of sensingsignal in DC measurement, and an AC testing method to acquire the sensing signal arerespectively proposed.(3) The finite element model of CNT cement-based composites is set up by usingMonte Carlo method and ANSYS12.0. The effect of aspect ratio, diameter andconcentration of CNT on the effective resistivity of composites is investigated withfinite element analysis (FEA). Furthermore, the effective resistivity calculated by FEAand the resistivity tested in experiment are respectively regressed through GeneralEffectvie Media equation. The effect of aspect ratio, diameter and concentration of CNTon the sensing property of composites is also discussed. Finally, the conduction andsensing mechanisms of the composites are analyzed with Simmons’ universal equationof tunnel effect.(4) A pre-cast and a cast-in-place self-sensing CNT cement-based compositecomponents are simultaneously integrated into concrete pavement in real road testing field. The feasibility of traffic detection with self-sensing CNT concrete pavement isinvestigated under different vehicle types, speeds and test conditions. Research resultsindicate that the use of self-sensing CNT concrete pavement is feasible for trafficdetection because it has good detection sensitivity and robustness.